The paper, published in Nature Communications, revises previous estimates of how much humans change Earth's land surface – such as via the destruction of tropical rainforests. It finds that, when accounting for multiple instances of change in the same place, 720,000 square kilometers (approximately 278,000 square miles) of land surface has changed annually since 1960 – an area, the authors note, "about twice the size of Germany."
These new estimates are a synthesis of high-resolution satellite imagery and long-term inventories of land use. Combining these two types of data sources, the authors write, allows them to examine land-use change in "unprecedented" detail.
Despite steadily increasing rates of land-use change over the latter half of the 20th century, the global rate has been decelerating since 2005. The authors attribute this slowdown to the 2007-08 financial crisis, which they hypothesize caused economic shifts in the global north that reverberated around the world.
A 'Careful Reconstruction'
"Land-use change" is any way in which humans modify the natural landscape. Some of these changes are permanent destruction, such as urban expansion. Other changes, such as cropland abandonment and forest restoration, may attempt to repair previous damage. It is a widespread phenomenon – humans have altered "about three-quarters of the Earth's land surface" in the past millennium, the authors write.
Land use is typically measured in one of two ways: by high-resolution satellite imagery, or by large-scale statistical surveys. But each of these methods has its drawbacks when assessing land-use change, the study says. Satellites can capture land use in high detail, but their records only extend back a few decades. Estimates based on satellite images also tend to miss some nuances of land use – such as the distinction between unmanaged grasslands and those used for grazing.
Statistical methods and surveys, such as those that the UN Food and Agriculture Organization (FAO) has been carrying out since 1961, extend further back in time than the satellite record, but at a much more coarse resolution. And little work has been done to combine these two approaches.
"The information on land and land-use change is very fragmented," Karina Winkler, the lead author of the study and a Ph.D. candidate in land-system dynamics at the Karlsruhe Institute of Technology and Wageningen University, tells Carbon Brief:
"The idea was to collect as many data [sources] as possible and bring them together."
Combining all of these disparate data sources, the authors write, also has the advantage of reducing the inconsistencies or limitations of any single dataset.
Winkler and her colleagues brought together more than 20 satellite land-use products and long-term surveys. The resulting dataset, which they termed the "Historic Land Dynamics Assessment plus" (HILDA+, for short), captures annual changes in land use across the globe with a resolution of 1km.
But not all land-use change is permanent. So rather than looking at "net" changes that only capture the overall transformation of an area, HILDA+ captures places where land use has changed multiple times – such as rotation between cropland and pasture. When these "gross" changes are summed up, the total extent of land-use change between 1960 and 2019 is 43m km2 – just under one-third of the total land surface of Earth.
The map below shows where both single-change (yellow shading) and multiple-change (red) events are occurring around the world. Instances of multiple-change events are dominant across Europe, India and the U.S., while single change events are widespread across South America, China and Southeast Asia.
Global instances of single (yellow) and multiple (red) land-use-change events. The pie charts show the total extent of change as a percentage of global land cover. Winkler et al. (2021)
Global land-use change nearly doubles when considering gross change, from 17% to 32% of Earth's land surface. And nearly two-thirds of this gross change is due to multiple-change events. Studying land-use change in this way – as an accumulation of all the changes occurring over time, rather than as net change – can help better account for the greenhouse gas emissions associated with land use, Winkler says.
A Source and a Sink
According to the Intergovernmental Panel on Climate Change's 2019 special report on climate change and land, nearly one-quarter of total human-caused greenhouse gas emissions between 2007 and 2016 were due to agriculture, forestry and other land use. In total, land use falls just behind electricity and heat production as the world's second-largest contributor to greenhouse gas emissions.
But land is also a major "sink" of greenhouse gases – for example, through the carbon taken up by forests. This balance of sources and sinks through land-use change, the IPCC report says, is a "key source of uncertainty" in considering the future of the land carbon cycle. Knowing the dynamics of past land-use change in finer detail can help inform the way climate modelers represent these changes, Winkler says.
"Land-cover change is really, really dynamic," professor Navin Ramankutty, a land-systems scientist at the University of British Columbia, tells Carbon Brief. Ramankutty, who was not involved in the study, adds:
"If you're just using net land-use changes over time, you might not actually capture the dynamic of carbon being taken back up by the land."
The new work on its own cannot provide much insight into how these gross land-use changes might affect the picture of climate change, Ramankutty says. "The devil is in the details," he explains:
"It's hard to say what the implications are [for climate change] without actually running [the new estimates] through a carbon-cycle model."
However, he adds, the updated estimates are "a much more careful reconstruction of how land has changed". He notes that it "seems more sophisticated than previous work" and that he would recommend using the new dataset.
Patterns of Change
Following the definitions used in the FAO's annual surveys, the researchers separate out six categories of land use: urban areas, cropland, pasture, unmanaged grassland, forest and sparsely vegetated land. Several notable patterns jump out when looking at what types of change are occurring where, the authors say.
For example, about half of the single-change events – or nearly 20% of the total changes – occur due to agricultural expansion, such as deforestation. And 86% of the multiple-change events are agriculture-related, predominantly occurring in the global north and select rapidly growing economies.
Averaged globally, land-use change steadily increased for nearly half a century since the FAO surveys began. But, in 2005, there was a "rather abrupt change" in this trend and land-use change began decelerating worldwide, the authors write.
The charts below depict the differences in land-use change rates between six geographical regions, as well as the worldwide average. The global rates of change can be defined by an acceleration period from 1960 to the early 2000s, followed by deceleration since about 2005.
Rates of change of land use in (clockwise from top left): North and Central America, Europe, central and eastern Asia, south-east Asia and Australia, Africa, South America, and globally.
Examining these changes in the context of global political and economic events, the researchers hypothesize that the "rate and extent of global land-use change is responsive to socio-economic developments and disruptions."
Although it is hard to prove such causation with certainty, they write that "the transition from accelerating to decelerating land-use change is related to market developments in the context of the global economic and food crisis" that occurred in the late 2000s. Increasing globalization and a fast-growing population drove expanding land use in the 1990s and early 2000s. As oil prices rose rapidly, peaking in 2008, demand for biofuels from the global north – but grown in the global south – rose, too.
However, in the aftermath of the 2007-08 global financial crisis, imports declined and agricultural expansion in the global south slowed as demand for commodity crops dropped off. Since then, reduced foreign investment and land acquisitions have meant the deceleration of land-use change has continued.
This phase shift from accelerating to decelerating land-use change is just one example of a larger pattern of "teleconnections," whereby economic changes in one region of the world can have far-flung effects on land-use elsewhere, Winkler says:
"Political changes in the global north are driving some land-intensive changes in the global south and these effects have increased since the 2000s or late '90s."
Changes in agricultural land use are more variable than changes in forest cover, the authors note, because agriculture is more responsive to external factors such as geopolitical shifts, extreme weather and global supply-chain disruptions.
In the future, Winkler plans to continue trying to tease out the impacts of socio-economic events on land-use change around the world, but she hopes that many others will take advantage of the new data for their own work. She tells Carbon Brief that the new dataset is "for many different interest groups to use. It's kind of a playground and a starting point for a new perspective on land-use change." She adds:
"The most important message is that when we look at the topic of land-use change with a finer lens or more detail…with this harmonising approach, we can track the speed of land-use change in a better way and we can also explore the background of why land-use change happens."
Reposted with permission from Carbon Brief.
Furthermore, the IEA's "renewable energy market update" forecasts nearly 40% higher growth in 2021 than it expected a year ago, putting wind and solar on track to match global gas capacity by 2022.
The Paris-based agency says a "huge" 280 gigawatts (GW) of renewable capacity – primarily wind and solar – was installed globally last year, some 45% higher than the level in 2019, after the largest annual increase in more than 20 years.
This "exceptional" level of annual additions will become the "new normal" in 2021 and 2022, the IEA says, with the potential for further acceleration in the years that follow.
Overall, the IEA says that renewables accounted for 90% of new electricity generating capacity added globally last year and that they will meet the same share in each of the next two years.
Raising Renewables
In its latest update, the IEA says wind and solar growth forecasts have been "revised upwards by over 25% from last year."
This is based on comparing the new forecast for growth in 2021 (red line in the chart below) to the "main case" published in November 2020 (dashed mid blue). Looking at the figures for 2022, the IEA's new forecast is 30% higher than the main one it published last November.
Annual global growth of wind and solar capacity, 2000-2025. Actual growth is shown in black, while various IEA forecasts are shown in red and shades of blue. Source: Carbon Brief analysis of IEA forecasts. Chart by Carbon Brief using Highcharts.
Wind and solar are now expected to surpass even the "accelerated case" outlined by the agency in November 2020 (dashed dark blue), in which they matched global gas capacity by 2022.
Moreover, the new forecast for 2021 is nearly 40% higher than the one published by the IEA just a year ago, in May 2020 (dashed light blue line).
At the time, the agency had expected renewable additions to be badly hit by the unfolding COVID-19 pandemic, but impacts on the sector were largely confined to the first quarter of the year.
Raise, Repeat
The IEA has repeatedly raised its expectations for wind and solar over the past decade, drawing fire from critics that say – in the words of a 2019 Reuters article – that it has "underplay[ed] the speed at which the world could switch renewable sources of energy."
Last year's flagship IEA World Energy Outlook made a major update to the agency's assumptions about the costs of financing the construction of wind and solar over the next two decades. This gave a significant boost to the agency's expectations for the growth of renewables.
But today's new report, which focuses on near-term growth in 2021 and 2022, contains even higher forecasts for wind and solar growth.
This is shown for solar in the chart below, with red triangles marking the solar growth figures in today's report, the red line showing historical data and the blue and black lines showing successive World Energy Outlooks for solar over the next 20 years, as published between 2009-2020.
Gigawatts of solar capacity added around the world each year (red line) and the IEA renewable market update 2021 (red triangles), as well as IEA World Energy Outlooks published between 2009-2020. Source: Carbon Brief analysis of IEA reports. Chart by Carbon Brief using Highcharts.
Explaining its new forecasts, the IEA points to a number of changes over the past year, as well as areas where its earlier expectations have proved too pessimistic.
The biggest changes in this year's forecast are for China, the IEA notes, where more projects are going ahead without government subsidies than expected. The update says:
"The pipeline of solar PV and wind plant projects accepting provincial electricity prices without additional subsidies has increased since last year, resulting in a more optimistic forecast."
The IEA has, therefore, increased its forecast for growth in China by 45%, boosting total additions in 2021 and 2022 from around 150GW to around 230GW, as shown in the chart below.
Wind and solar growth during 2021 and 2022, according to the IEA's November 2020 forecast (green) and its May 2021 figures (blue). Forecast capacity growth is shown by the bars and the left axis. The percent revision between forecasts is shown by the dots and the right axis.Source: IEA Renewable Energy Market Update 2021
The new China forecast for 2021 and 2022 is lower than the growth seen in 2020, when developers rushed to secure subsidies before they expired, but the IEA now sees less of a slowdown than it had previously expected.
Elsewhere, the IEA has boosted its U.S. forecasts by more than 20% thanks to the expected extension of renewable energy tax credits.
The forecast does not yet include the Biden administration's new emissions reduction targets or its infrastructure bill, which the IEA says would boost renewable growth after 2022, if enacted.
It also points to better-than-expected solar auction volumes in India during 2020, but adds that the ongoing COVID-19 surge in the country creates "short-term uncertainty."
The IEA says there were "record-breaking" competitive auctions for renewable contracts last year, with India and China securing almost 55GW of new capacity at average prices of $60 per megawatt hour (MWh) for wind and $47/MWh for solar.
There was another record-breaking year for corporate renewable energy deals, the IEA adds, with companies signing "power purchase agreements" for nearly 25GW in 2020 – a 25% increase.
In a press release announcing the new figures, IEA chief executive Fatih Birol says:
"Wind and solar power are giving us more reasons to be optimistic about our climate goals as they break record after record. Last year the increase in renewable capacity accounted for 90% of the entire global power sector's expansion…A massive expansion of clean electricity is essential to giving the world a chance of achieving its net-zero goals."
The update says renewables will again meet 90% of the global power sector's capacity growth in 2021 and 2022.
Reposted with permission from Carbon Brief.
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How Much Do Solar Panels Cost to Install?
To begin with, let's take a look at the basic price range for solar panel installation. According to the most recent U.S. Solar Market Insight report, in the first quarter of 2021, the national average price of a residential solar system was $2.94 per watt, which would mean a 5 kWh system would cost $14,700 and a 10 kWh system would cost $29,400.
The exact price you'll pay for solar panels will depend on a number of factors, including your geographic location, the size of your home and more.
Now, you might rightly wonder: What exactly are you paying for? The solar panels themselves usually make up just about a quarter of the total cost. Remaining expenses include labor, maintenance and additional parts and components (such as inverters).
What Factors Determine Solar Pricing?
As mentioned, there are a few key things that can lead to variation in solar system installation costs. Analyzing these can help you determine whether solar panels are worth it for your home. Let's take a look at them in greater detail.
Your Electrical Needs
The solar panels themselves will be rated for a particular wattage, which reflects the amount of energy they can absorb for storage and ultimately for power generation. You will actually pay according to wattage, which means that the greater your household energy needs, the more you'll have to spend to get the correct number of solar panels.
So, how do you determine how much energy you need for your home? The best way to figure this out is through a consultation with a solar installer. (We recommend shopping smart by requesting free consultations with two or three top solar companies in your area.)
Your installer will evaluate your home energy needs based on total square footage, the number of people who live in your home, the number of appliances and power-draining devices that you have connected and more. It can then recommend the ideal solar panel system size to accommodate your energy usage.
Type of Panels and Other Components
Variation in manufacturing can also affect the cost of solar panels. There are three basic types of solar panels, two of which are commonly used residentially: monocrystalline and polycrystalline panels. Of these two, monocrystalline options tend to be more energy-efficient and thus may provide you with greater savings in the long run. They are also a bit pricier on the front end. With that said, homeowners with a smaller roof surface area may benefit from getting the most efficient solar panels, even if the initial cost is a bit steeper.
Other components you'll need to purchase include inverters, wiring, charge controllers, mounts and more. The quality of these materials can affect your total solar system cost. For example, if you spring for the best solar batteries, they may add a few thousand dollars to your investment.
Geographic Location
Another factor that can have a big impact on solar pricing? Your geographic area. Solar installation tends to be most cost-effective in parts of the country that get a lot of sun exposure, and thus a lot of photovoltaic light. This basically means that solar panels can operate more efficiently, and in many cases means that fewer total panels are needed. Those who live in states like California, Florida and Arizona — or really any areas of the Sun Belt or Southwest — will likely get the most out of their home solar power systems.
Tax Incentives
Both state and federal governments have established incentive programs to encourage homeowners to buy solar panels. There is currently a 26% federal solar tax credit, called an Investment Tax Credit (ITC), available for homeowners who install residential solar panels between 2020 and 2022. It is scheduled to reduce to 22% in 2023 and may not be extended thereafter.
Local incentives vary by state, but most of the best solar panel installers will help you identify and apply for these programs so you don't miss out on savings.
Additional Factors
There are plenty of other factors that can impact solar panel installation costs. Different vendors are going to offer different levels of customization, expertise and consumer protections (including guarantees and warranties). The bottom line? It is wise to shop around a bit, determine the average cost of solar panels in your area and evaluate the value of services offered by a few solar installation companies.
Solar Panel Price Vs. Return on Investment
Clearly, your upfront solar panel installation cost may be a little steep. Now, let's look at the flipside: How much money will you actually save? And will your energy savings be enough to offset the initial cost of your solar energy system?
It is not unreasonable to think that you can cut your monthly utility bills by as much as 75% or more by switching to solar energy. Of course, the specific dollar amount will depend on where you live, the size of your home and the number of people in your household.
One way to look at it: The average household energy bill is somewhere between $100 and $200 monthly. It would probably take about 15 years for your energy savings to cancel out the cost of solar panel installation. In other words, within a decade and a half or so, your solar system might pay for itself. Factor in savings from tax rebates and other incentives, and most solar systems pay for themselves in closer to seven or eight years.
Note that most solar energy companies offer free solar calculators, which help you arrive at a ballpark for monthly energy savings. While these calculators are imprecise, they can certainly give you a general sense of the financial benefits you will experience when you convert to solar energy.
Free Quote: See How Much You Can Save on Solar Panels
Fill out this 30-second form to get a quote from one of the best solar energy companies in your area. You could save up to $2,500 each year on your electric bills and receive tax rebates.
Frequently Asked Questions About the Cost of Solar Panels
As you continue to weigh the pros and cons of solar energy, it's natural to have a few questions. The best way to resolve these is really to set up a solar consultation with a local expert, but in the meantime, here are a few general answers to some of the most common solar inquiries.
How much will it cost to maintain my solar energy system?
In general, solar systems are designed to run smoothly for decades without requiring any maintenance or upkeep. As such, you should not really need to factor maintenance into the equation for the first 20 years or so after you install your system. (And most solar companies will offer you warranties and guarantees to give peace of mind on this front.)
How will solar energy impact my property values?
Many homeowners want to know how going solar will impact the value of their homes. Going solar increases property values. In fact, the U.S. Department of Energy has reported buyers are willing to pay an average premium of about $15,000 for a home with a solar panel system. With that said, you are only going to see your property values go up if you own your solar system outright, as opposed to leasing it.
How can I finance the cost of solar panels?
Different solar installers may offer different financing plans, allowing consumers some flexibility. With that said, there are three basic options for paying for your solar energy system:
- Purchase your solar energy system outright (that is, pay in cash).
- Take out a solar loan to purchase the system, then pay it back with interest.
- Lease your system; you will pay less month-to-month but won't actually own the system yourself.
Which is better, buying or leasing my solar system?
It all depends on your motivation for going solar. If you want to maximize long-term savings and increase the value of your home, then purchasing your solar system is usually best. However, if you just want a low-maintenance way to reduce monthly energy costs and practice environmental stewardship, then leasing might be a better option. Also note that leasing can be a good option for those who do not plan on being in their home for exceptionally long.
How can I be sure my roof will accommodate a solar system?
If your roof faces south, has ample space and has little to no shade cover, it should work just fine. Even roofs that are not optimal can still be utilized with a few tweaks and adjustments. Your solar energy consultant will advise you on whether your home is a good fit for solar energy.
How long will my solar energy system last?
Solar systems are designed to be exceptionally durable. With just the most basic upkeep, most solar energy systems should continue to work and produce power for anywhere from 25 to 35 years.
Make the Best Choice About Solar Energy
Solar energy is not right for every homeowner, nor for every home. With that said, many homeowners will find that the initial cost of solar panels is more than offset by the long-term, recurring energy savings. Make sure you factor in cost, energy needs, tax incentives, home value and more as you seek to make a fully informed decision about whether to embrace solar power.
These longer periods of stratification could have "far-reaching implications" for lake ecosystems, the paper says, and can drive toxic algal blooms, fish die-offs and increased methane emissions.
The study, published in Nature Communications, finds that the average seasonal lake stratification period in the northern hemisphere could last almost two weeks longer by the end of the century, even under a low emission scenario. It finds that stratification could last over a month longer if emissions are extremely high.
If stratification periods continue to lengthen, "we can expect catastrophic changes to some lake ecosystems, which may have irreversible impacts on ecological communities," the lead author of the study tells Carbon Brief.
The study also finds that larger lakes will see more notable changes. For example, the North American Great Lakes, which house "irreplaceable biodiversity" and represent some of the world's largest freshwater ecosystems, are already experiencing "rapid changes" in their stratification periods, according to the study.
'Fatal Consequences'
As temperatures rise in the spring, many lakes begin the process of "stratification." Warm air heats the surface of the lake, heating the top layer of water, which separates out from the cooler layers of water beneath.
The stratified layers do not mix easily and the greater the temperature difference between the layers, the less mixing there is. Lakes generally stratify between spring and autumn, when hot weather maintains the temperature gradient between warm surface water and colder water deeper down.
Dr Richard Woolway from the European Space Agency is the lead author of the paper, which finds that climate change is driving stratification to begin earlier and end later. He tells Carbon Brief that the impacts of stratification are "widespread and extensive," and that longer periods of stratification could have "irreversible impacts" on ecosystems.
For example, Dr Dominic Vachon – a postdoctoral fellow from the Climate Impacts Research Centre at Umea University, who was not involved in the study – explains that stratification can create a "physical barrier" that makes it harder for dissolved gases and particles to move between the layers of water.
This can prevent the oxygen from the surface of the water from sinking deeper into the lake and can lead to "deoxygenation" in the depths of the water, where oxygen levels are lower and respiration becomes more difficult.
Oxygen depletion can have "fatal consequences for living organisms," according to Dr Bertram Boehrer, a researcher at the Helmholtz Centre for Environmental Research, who was not involved in the study.
Lead author Woolway tells Carbon Brief that the decrease in oxygen levels at deeper depths traps fish in the warmer surface waters:
"Fish often migrate to deeper waters during the summer to escape warmer conditions at the surface – for example during a lake heatwave. A decrease in oxygen at depth will mean that fish will have no thermal refuge, as they often can't survive when oxygen concentrations are too low."
This can be very harmful for lake life and can even increase "fish die-off events" the study notes.
However, the impacts of stratification are not limited to fish. The study notes that a shift to earlier stratification in spring can also encourage communities of phytoplankton – a type of algae – to grow sooner, and can put them out of sync with the species that rely on them for food. This is called a "trophic mismatch."
Prof Catherine O'Reilly, a professor of geography, geology and the environment at Illinois State University, who was not involved in the study, adds that longer stratified periods could also "increase the likelihood of harmful algae blooms."
The impact of climate change on lakes also extends beyond ecosystems. Low oxygen levels in lakes can enhance the production of methane, which is "produced in and emitted from lakes at globally significant rates," according to the study.
Woolway explains that higher levels of warming could therefore create a positive climate feedback in lakes, where rising temperatures mean larger planet-warming emissions:
"Low oxygen levels at depth also promotes methane production in lake sediments, which can then be released to the surface either via bubbles or by diffusion, resulting in a positive feedback to climate change."
Onset and Breakup
In the study, the authors determine historical changes in lake stratification periods using long-term observational data from some of the "best-monitored lakes in the world" and daily simulations from a collection of lake models.
They also run simulations of future changes in lake stratification period under three different emission scenarios, to determine how the process could change in the future. The study focuses on lakes in the northern hemisphere.
The figure below shows the average change in lake stratification days between 1900 and 2099, compared to the 1970-1999 average. The plot shows historical measurements (black), and the low emission RCP2.6 (blue), mid emissions RCP6.0 (yellow) and extremely high emissions RCP8.5 (red) scenarios.
Change in lake stratification duration compared to the 1970-1999 average, for historical measurements (black), the low emission RCP2.6 (blue) moderate emissions RCP6.0 (yellow) and extremely high emissions RCP8.5 (red). Credit: Woolway et al (2021).
The plot shows that the average lake stratification period has already lengthened. However, the study adds that some lakes are seeing more significant impacts than others.
For example, Blelham Tarn – the most well-monitored lake in the English Lake District – is now stratifying 24 days earlier and maintaining its stratification for an extra 18 days compared to its 1963-1972 averages, the study finds. Woolway tells Carbon Brief that as a result, the lake is already showing signs of oxygen depletion.
Climate change is increasing average stratification duration in lakes, the findings show, by moving the onset of stratification earlier and pushing the stratification "breakup" later. The table below shows projected changes in the onset, breakup and overall length of lake stratification under different emission scenarios, compared to a 1970-1999 baseline.
The table shows that even under the low emission scenario, the lake stratification period is expected to be 13 days longer by the end of the century. However, in the extremely high emissions scenario, it could be 33 days longer.
The table also shows that stratification onset has changed more significantly than stratification breakup. The reasons why are revealed by looking at the drivers of stratification more closely.
Warmer Weather and Weaker Winds
The timing of stratification onset and breakup in lakes is driven by two main factors – temperature and wind speed.
The impact of temperature on lake stratification is based on the fact that warm water is less dense than cool water, Woolway tells Carbon Brief:
"Warming of the water's surface by increasing air temperature causes the density of water to decrease and likewise results in distinct thermal layers within a lake to form – cooler, denser water settles to the bottom of the lake, while warmer, lighter water forms a layer on top."
This means that, as climate change causes temperatures to rise, lakes will begin to stratify earlier and remain stratified for longer. Lakes in higher altitudes are also likely to see greater changes in stratification, Woolway tells Carbon Brief, because "the prolonging of summer is very apparent in high latitude regions."
The figure below shows the expected increase in stratification duration from lakes in the northern hemisphere under the low (left), mid (center), and high (right) emission scenarios. Deeper colors indicate a larger increase in stratification period.
Expected increase in stratification duration in lakes in the northern hemisphere under the low (left), mid (centre) and high (right) emissions scenarios. Credit: Woolway et al (2021).
The figure shows that the expected impact of climate change on stratification duration becomes more pronounced at more northerly high latitudes.
The second factor is wind speed, Woolway explains:
"Wind speed also affects the timing of stratification onset and breakdown, with stronger winds acting to mix the water column, thus acting against the stratifying effect of increasing air temperature."
According to the study, wind speed is expected to decrease slightly as the planet warms. The authors note that the expected changes in near-surface wind speed are "relatively minor" compared to the likely temperature increase, but they add that it may still cause "substantial" changes in stratification.
The study finds that air temperature is the most important factor behind when a lake will begin to stratify. However, when looking at stratification breakup, it finds that wind speed is a more important driver.
Meanwhile, Vachon says that wind speeds also have implications for methane emissions from lakes. He notes that stratification prevents the methane produced on the bottom of the lake from rising and that, when the stratification period ends, methane is allowed to rise to the surface. However, according to Vachon, the speed of stratification breakup will affect how much methane is released into the atmosphere:
"My work has suggested that the amount of accumulated methane in bottom waters that will be finally emitted is related to how quickly the stratification break-up occurs. For example, a slow and progressive stratification break-up will most likely allow water oxygenation and allow the bacteria to oxidise methane into carbon dioxide. However, a stratification break-up that occurs rapidly – for example after storm events with high wind speed – will allow the accumulated methane to be emitted to the atmosphere more efficiently."
Finally, the study finds that large lakes take longer to stratify in spring and typically remain stratified for longer in the autumn – due to their higher volume of water. For example, the authors highlight the North American Great Lakes, which house "irreplaceable biodiversity" and represent some of the world's largest freshwater ecosystems.
These lakes have been stratifying 3.5 days earlier every decade since 1980, the authors find, and their stratification onset can vary by up to 48 days between some extreme years.
O'Reilly tells Carbon Brief that "it's clear that these changes will be moving lakes into uncharted territory" and adds that the paper "provides a framework for thinking about how much lakes will change under future climate scenarios."
Reposted with permission from Carbon Brief.
The study also finds that climate change is a "significant contributor" to a 21% increase in pollen levels since 1990. The authors note that the increase in tree pollen levels is bigger than the increase in either grass or weed pollen.
"Climate change is already worsening pollen seasons," the lead author of the study tells Carbon Brief, adding that this is "bad news for people with respiratory health problems."
'Worsening' Pollen Seasons
Pollen is a powdery substance that is released into the air by plants, such as grasses, weeds, and trees. Pollen grains float through the air – if they land on another plant of the same species, they can fertilize it to produce seeds for a new plant.
Plants only release pollen into the air throughout the warm "pollen season". For the US, this begins – depending on the state – around February and continues throughout the summer.
Research shows that warmer temperatures and higher CO2 levels can shift pollen seasons and increase pollen levels. However, this study is the first to calculate the contribution of climate change to historical pollen data trends, lead author Dr William Anderegg from the University of Utah tells Carbon Brief:
"The central new aspect of this study is a detection of a 'fingerprint' of climate change on pollen trends in the US and Canada and in attributing how much of these trends is likely due to climate change."
To determine the impact of climate change on the pollen season, the team analyzed pollen records from 60 cities in the US and Canada from 1990–2018. The data are shown below.
The map on the left shows changes in pollen level – in other words, how much pollen the air is carrying. Red circles indicate rising pollen levels over time and blue circles indicate falling levels. Circle size corresponds to how many years of data were available – larger circles mean more years of data are used.
Similarly, the figure on the right shows changes in the start date of the pollen season. Red circles indicate an earlier start date and blue circles indicate a later start date.
Pollen data from 60 stations in the US and Canada. Changes in "pollen integral" (top) and changes in pollen season start date (bottom). Red circles indicate higher pollen levels and earlier start dates, respectively. Circle size is proportional to the number of years of data at each station. Source: Anderegg et al. (2021).
The study also shows that the North America pollen season has become around eight days longer and has also shifted to start around 20 days earlier. This suggests a "seasonal shift of pollen loads to earlier in the year," according to the paper.
The authors find that between 1990-2018 the average annual pollen level increased by 21%. The map shows that the largest, most consistent increases were seen in Texas and the midwestern US.
Allergic Reaction
There are three main types of pollen that can cause allergic reactions in humans, such as hayfever – "tree pollen," "grass pollen" and "weed pollen". Many people are more allergic to some types than others.
The impacts of climate change are different for different plants, so the authors analyzed pollen trends for each of these three plant types individually. They found that, of the three main plant types, the biggest increase in pollen level is from tree pollen.
The longer pollen season and the higher levels of pollen in the air means that peoples' exposure to allergenic pollen has "increased significantly" over recent decades, the paper notes. Anderegg adds that this is "bad news" for those with respiratory health problems and that it is "likely to get worse in coming decades."
Dr Claudia Traidl-Hoffman from the Technical University of Munich, who was not involved in the study, tells Carbon Brief that "allergies are the most common chronic inflammatory diseases and will be further fueled by climate change."
Climate Changes 'Worsens' Pollen Seasons
As well as analyzing changes in the pollen season, the authors determined how much climate change contributed to these trends.
To do this, the authors tested a range of annual and seasonal climate variables, including temperature, rainfall, frost days and atmospheric CO2 level. These analyses were run on 22 Earth system models from the fifth and sixth Coupled Model Intercomparison Projects (CMIP).
The study finds that average annual temperature is the strongest predictor of changes to annual pollen level, spring level, pollen season length and pollen season start date.
Anderegg tells Carbon Brief that temperature is a "key determinant" in plant development and that "a longer growing season due to climate change appears to mean a longer pollen season."
Dr Thanos Damialis from the University Centre for Health Sciences at University Hospital Augsburg, who was not involved in the study, tells Carbon Brief how climate change can affect pollen production:
"Land eutrophication and increased temperatures, along with higher urbanity and anthropogenic emissions – such as nitrogen dioxide – are known to have a multiple effect on plants: they produce more biomass, more flowers, the plant produces more pollen, which all result in more airborne pollen in urban environments."
The figure below shows the contribution of climate change to annual pollen level (dark red), spring pollen level (light red), pollen season start date (dark green) and pollen season length (light green). For each of these factors, two different time periods are shown – 1990-2018 and 2003-2018. The black line shows the model average.
Impact of climate change on annual pollen level (dark red), spring pollen level (light red), pollen season start date (dark green) and pollen season length (light green). Source: Anderegg et al (2021).
The study concludes that climate change is responsible for roughly 50% of the changes to the pollen duration and start time, and 8% of the changes to pollen level.
The authors note that the impact of climate change is more significant in spring than annually due to a "seasonal compensation" effect, whereby a decrease in summer pollen levels could lower the annual average.
The figure above also shows that the influence of climate change on pollen seasons has become larger over time. For example, the study finds that between 1990-2018 climate change was responsible for between 35-66% of the shift in pollen start date. However, between 2003-2018, it contributed to between 45-84% of this shift.
These findings suggest that the impact of climate change on the pollen season is getting stronger over time, the authors say.
The paper notes that the increase in monitoring stations in recent years could also have influenced this result. However, the authors add that the results are robust when "sensitivity analyses" are conducted around the number of stations included and the longevity of station observations.
Traidl-Hoffman says the study is of "utmost importance" for investigating the impacts of climate change on health. She tells Carbon Brief:
"Climate change is impacting enormously on our health and allergic diseases are in the first line of importance."
Reposted with permission from Carbon Brief.
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The decline in emissions reflects the headwinds already affecting the Indian economy since early 2019, and increasing renewable energy generation. But our analysis of official Indian data across the nation's entire 2019-20 fiscal year shows the fall has steepened in March, due to measures to combat the coronavirus pandemic. The country's CO2 emissions fell by an estimated 15% during the month of March and are likely to have fallen 30% in April.
As with the global CO2 impact of the pandemic, the longer-term outlook for India's emissions will be shaped, to a significant degree, by the government response to the crisis. This response is now starting to emerge – as set out below – and will have major long-term implications for India's CO2 emissions and air quality trajectory.
Coal Bearing Brunt of Demand Crunch
As lower power demand growth and competition from renewables weakened the demand for thermal power generation throughout the past 12 months, the drop-off in March was enough to push generation growth below zero in the fiscal year ended March, the first time this has happened in three decades.
Over the preceding decade, thermal power generation grew by an average of 7.5% per year. As seen in the figure below, the dramatic drop-off in total power demand was entirely borne by coal-based generators, amplifying the impact on emissions.
Coal-fired power generation fell 15% in March and 31% in the first three weeks of April, based on daily data from the national grid. In contrast, renewable energy (RE) generation increased by 6.4% in March and saw a slight decrease of 1.4% in the first three weeks of April.
Daily power generation by source and by year in India. Source: POSOCO. Chart by Carbon Brief using Highcharts.
The fall in total coal demand extends beyond the power sector and is evident in data on coal supply. In the fiscal year ending March, coal sales by the main coal producer Coal India Ltd fell by 4.3%, while coal imports increased 3.2%, implying that total coal deliveries fell by 2% and signaling the first year-on-year fall in consumption in two decades.
The trend steepened in March, with coal sales falling 10% while coal imports fell 27.5% in March, meaning that total deliveries of coal to end users fell by 15%, in line with the reduction in power generation.
In March, coal output increased 6.5% even as sales fell by a record amount. Also, during the full year, more coal was mined than sold, indicating that the reason for the drop was on the demand side.
Oil Demand: From Weak to Negative
Similar to electricity demand, oil consumption has been slowing down since early 2019. This is now compounded by the dramatic impact of the Covid-19 lockdown measures on transport oil consumption. During the national lockdown, oil consumption fell 18% on year in March 2020.
As a result of low demand due to the coronavirus outbreak and already slower demand growth earlier in the year, consumption during the fiscal grew at 0.2%, the slowest in at least 22 years. Natural gas consumption increased 5.5% in the first 11 months of the fiscal year, but is expected to fall by 15-20% during the lockdown.
Crude oil production in India decreased by 5.9% compared to last financial year and a 5.2% drop has been observed in natural gas production during the same time. Refinery production – in terms of crude oil processed – also fell by 1.1% over the last financial year, compared to 2018-19.
Crude steel production dropped by 22.7% in March 2020 compared to the previous month and, cumulatively, the financial year 2019-20 saw a decline of 2.2% compared to last year, according to Ministry of Steel data.
CO2 Emissions Down 30% in April
Using the indicators above for coal, oil and gas consumption, we estimate that CO2 emissions fell by 30m tonnes of CO2 (MtCO2, 1.4%) in the fiscal year ending March, in what is likely to have been the first annual decline in four decades.
Annual emissions from fossil fuel use in India, millions of tonnes of CO2, 1965-2020. Figures for 2009 onwards correspond with financial years ending that March, with the 2020 number showing fiscal year 2019-20. Source: Analysis of Indian government data for this article and BP Statistical Review of World Energy. Chart by Carbon Brief using Highcharts.
Furthermore, emissions fell by 15% year-on-year in March and by 30% in April. The April estimate is based on power-sector emissions estimated from daily generation data. This assumes oil consumption falls as much in April as in March, which is very likely to be conservative as the national lockdown is continuing until the end of the month, and gas consumption falls 15-20% as projected.
Government Response
While the current crisis is having a significant impact on India's CO2 emissions in the short term, it could also influence the longer-term trajectory of India's energy use and emissions.
Although the situation is only beginning to unfold, three possible consequences are already emerging:
- Post-crisis economic stimulus could be directed towards reinvigorating the country's renewable energy program.
- Plummeting electricity demand has brought the power industry's long-brewing financial problems to a head, necessitating bailouts with the potential for structural changes.
- Experience of exceptional air quality could add momentum to efforts against air pollution, resulting in strengthened targets and standards.
In each case, the crisis could act to catalyse, reinforce or accelerate the factors that have already been driving Indian policymaking in this area.
For example, the Indian government has already started talking about support for renewable energy as a part of the recovery, alongside similar statements by European leaders. One reason for this continued support is the fact that solar already offers far cheaper electricity than coal.
A recent auction secured 2,000 megawatts (MW) of new solar capacity at an average of 2.55-2.56 rupees per kilowatt hour (Rs/kWh, around $34 per megawatt hour). This result came despite the auction being held during the lockdown amid a period of severe uncertainty over the future market and financial situation.
In contrast, the average cost of a unit of electricity from India's biggest coal generator, the National Thermal Power Corporation (NTPC), stood at 3.38 Rs/kWh in the financial year 2018-19 ($45/MWh). This figure will likely keep moving upwards with every passing year due to inflation, increasing operational costs and with implementation of stricter emission standards.
Another example of Indian government support for the renewable industry came in early April when it stressed the "must-run" status of wind and solar projects and called on distribution companies to make timely payments to power generators.
The Ministry of New and Renewable Energy also extended the timelines for renewable energy projects to be completed for the period of the lockdown and the following 30 days. This will safeguard renewable energy developers from penalties arising due to delays from their committed schedules.
The ministry has also written to various states in recent weeks to give a "major push" to domestic renewable manufacturing capacity. Increased domestic supply will strengthen the renewable energy program by strengthening supply chains and political weight for the industry, as long as it does not give rise to excessive protectionism.
Blue-Sky Thinking
Over the past year, CO2 emissions as well as air pollution levels have declined. More recently, the sight of blue skies during the national lockdown across the country has created a sense of optimism among the public as well as policymakers that the air in India can be cleaned, if appropriate steps are taken.
Since many of the major sources of pollution – transport, power stations and industry – are also responsible for significant shares of the country's CO2 output, any strengthening of air quality standards – or their implementation – would have knock-on effects on emissions.
Earlier last year, in response to building public pressure, the environmental ministry announced India's first-ever National Clean Air Programme. This aims to reduce particulate matter pollution levels across 102 cities by 20-30% by 2024.
The program also pointed out that India's national ambient air quality standards (NAAQS), dating back to 2009, need revision. The standards are much weaker than the World Health Organization guidelines and there is more evidence of health impacts of air pollution being reported even at low concentrations of pollutants.
The recent experience of cleaner air and the drastic drop in pollution levels due to coronavirus lockdowns have started these conversations to strengthen the NAAQS among public, research institutes and civil society organizations. As a result, any return of India's poor air quality and smog can be expected to trigger a stronger public response.
Power-Sector Bailouts
As demand for thermal power generation plummets, so too do the earnings of India's electricity industry. In this way, the coronavirus crisis has brought the long-brewing financial woes of the country's power sector to a head.
The Indian government is working to finalize an economic relief package for the sector, initially pegged at INR 70,000 crore ($9bn) and now reportedly worth INR 90,000 crore ($12bn).
The sector was already struggling before the coronavirus crisis, making it a major source of bad loans and financial distress.
The reasons behind the chronic financial losses of the power industry and dependence on government bailouts are easy enough to see. Discounted electricity tariffs are offered for agricultural and domestic consumers, with farmers even being provided with electricity for free, and losses covered from industrial and commercial consumers and state budgets. There are major losses in transmission and theft of power. Distribution companies have committed to purchasing excessive amounts of power as a part of a push to expand thermal power generation, leading to the country's coal power overcapacity issue.
If the forthcoming government bailout allows these structural problems to persist then it could mean old coal power stations are able to continue operating, entrenching the country's dependence on fossil-fired generation. On the other hand, the bailout could be conditioned on reforms and restructuring, facilitating the achievement of national clean-energy goals.
There are already calls for a green recovery package in India. These questions — re-invigorating the renewable energy program, mitigating the rebound of air pollution and addressing the structural problems of the thermal power sector — will be at the heart of determining the outcome.
Reposted with permission from Carbon Brief.
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And the number of people exposed to such events, also known as "compound hot extremes," is likely to increase "several-fold" as temperatures continue to climb in the coming decades, the study authors tell Carbon Brief.
If global temperatures reach 2 C — the upper limit set by countries in the Paris agreement — the frequency of compound hot extremes could more than double across the northern hemisphere, when compared to 2012, the research finds.
However, if greenhouse gas emissions are not curbed, compound hot extremes could become eight times more frequent by the end of the century.
The study sets out "clear evidence" that human-caused climate change is leaving its mark on extreme heat events, another scientist tells Carbon Brief.
Day and Night
The new study, published in Nature Communications, looks specifically at "compound hot extremes" — a 24-hour period in summer where hot daytime temperatures are followed by similar nightime temperatures. (Temperatures are considered "hot" if they are in the top 10% of temperatures experienced by a region from 1960-2012.)
These kinds of events pose a particularly high danger to human health, explain study authors Dr Yang Chen, a climate extremes scientist from the Chinese Academy of Meteorological Sciences, and Dr Jun Wang, a climate and meteorological scientist from the Institute of Atmospheric Physics in China. In a joint interview, they tell Carbon Brief:
Simply put, compound hot extremes deprive humans of the valuable chance of relief, which could have been provided by the 'cooling-off' effects of a nighttime low.
Such conditions occurred during the 2003 summer heatwave in Europe, which saw 70,000 deaths across 16 countries, the authors say. Another example is the 1995 Chicago heatwave, which led to more than 700 heat-related deaths in just five days.
The study is the first to present "a complete storyline on compound hot extremes" — investigating how they have changed, the role of climate change in this and how they might increase in the future, the authors say.
The results show that compound hot extremes "are significantly increasing and will continue to increase in frequency and intensity" across the northern hemisphere, say Chen and Wang:
These increases in heat hazards will translate into several-fold increases in population exposure to them. The rise of anthropogenic emission of greenhouse gas emissions is to blame for these increases.
Burning Up
For the first part of their study, the authors analysed the "fingerprint" of human-caused climate change on compound hot extremes to date. To do this, they conducted an "attribution" analysis.
This involves using climate models to produce two sets of simulations: one including all the factors that affect the climate, including human-caused greenhouse gas emissions, volcanic eruptions and solar variability, and one including all of these factors except for greenhouse gas emissions.
The researchers then compared the frequency and intensity of compound hot extremes in both of these scenarios.
They found that only the scenario including human-caused greenhouse gas emissions could closely reproduce the pattern of compound hot extremes observed from 1960 to 2012. In their research paper, the authors write:
We find that the summer-mean warming over 1960-2012 largely dictates the past increases in frequency and intensity of compound hot extremes during that period in both observations and simulations.
The maps below show observed changes in summertime compound hot extreme frequency (left) and intensity (right) across the northern hemisphere from 1960-2012.
The left-hand map shows changes in the number of compound hot extreme days per decade (yellow to red for increases; light to dark blue for decreases), while the right-hand map shows changes in the average temperature of compound hot extremes per decade (same color scale).
Contributions from changing temperature mean and variability. Wang et al. (2020)
The map shows that increases in the frequency and intensity of compound hot extremes are widespread across the northern hemisphere, with parts of continental Europe and China particularly affected.
(Gaps in the data prevented the researchers from analysing changes in the most southern parts of the northern hemisphere, the authors say in their research paper.)
While the global pattern of increases is best explained by human-caused global warming, it is possible that some regional differences may be explained by other factors, the authors say.
For example, the drying of soils could help to explain local variation of heat extremes, the authors say in their research paper.
This is because dry soils accumulate heat during the day and release it at night, Wang and Chen say, making night hot extremes and, therefore, compound hot extremes, more likely.
Furnace Forecast
The authors also used climate models to project possible future changes to compound hot extremes until 2100. They investigated two scenarios: one "intermediate mitigation" pathway with moderately high greenhouse gas emissions ("RCP4.5") and one with very high greenhouse gas emissions ("RCP8.5").
Within each emissions scenario, they also looked at the changes to compound hot extremes expected if the world reaches 1.5 C and 2 C of global warming, which are the temperature limits set by the Paris agreement.
The charts below show the average expected change in the number of summertime compound hot extreme days (purple line), as well as independent hot days (blue line) and independent hot nights (turquoise line) across the northern hemisphere under RCP4.5 (top) and RCP8.5 (bottom) until 2100. (Compound extremes are where a hot day is followed by a hot night, whereas an "independent hot day" is when a hot day is not followed by a hot night.)
On the charts, red circles point out when the temperature limits of 1.5 C and 2 C will be breached in each scenario. The bottom chart also highlights when 4C could be breached. The various data points represent results from different climate models.
(It is worth noting that events are considered to be compound or independent. So, a 24-hour period where a hot day is followed by a hot night would be considered a compound extreme, but not an independent hot day or hot night.)
Constrained projections of summertime hot extremes. Wang et al. (2020)
The results show that the average number of compound hot extreme days across the northern hemisphere in summer would more than double if temperatures reach 2 C, when compared to 2012.
Keeping temperatures at 1.5 C could see five fewer compound hot extreme days across the northern hemisphere, on average, when compared to 2 C, the research adds.
If greenhouse gas emissions are extremely high (RCP8.5), the number of summertime compound hot extremes could increase eight-fold by 2100, when compared to 2012, the results show.
The charts also show that compound hot events are expected to increase at a much more rapid rate than independent hot day or hot night events.
This is chiefly because climate change is known to have a larger effect on nightime temperatures than daytime temperatures, the authors say.
Therefore, as the chances of hot nights become higher, the chances of compound hot events also increase — and, so, the chances of a hot day or night occurring independently decreases, explain Chen and Wang.
‘Clear Evidence’
The findings reinforce "the urgency in reducing emission of greenhouse gases" for policymakers, say Chen and Wang:
We should keep the point in mind that as the globe warms, future summers are increasingly dominated by compound hot extremes and become more uncomfortable. Namely, a hot day accompanied by a hot night without a relief window for humans might become a 'new norm'. As a result, vigilance against excess heat should be kept through day and night.
The study is "impressively comprehensive," says Dr Eunice Lo, a research associate in climate extremes from the University of Bristol, who was not involved in the research. She tells Carbon Brief:
I think the main take home message from this study is that we should use consecutive day-night hot extremes as a major heat-health indicator for policymaking, as compound hot extremes are projected to have larger future increases in frequency and intensity then hot days or nights.
The findings produce "clear evidence" that human-caused climate change is leaving its mark on extreme heat events, says Prof Peter Stott, who leads on climate monitoring and attribution at the Met Office Hadley Centre. Stott, who was also not involved in the research, tells Carbon Brief:
I don't find the conclusions of the study very surprising, but I do like the way the authors have comprehensively set out the implications – the clear evidence that the changes to date are driven by human emissions and the clear evidence that future changes will result in significant increases in the frequency and intensity of these compound extremes worldwide.
Reposted with permission from Carbon Brief.
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This would mean renewables matching coal as the joint-largest contributors to the global electricity mix in 2024, according to Carbon Brief analysis of new forecasts in the International Energy Agency (IEA) Renewables 2019 report.
The analysis is based on the IEA's "accelerated case," in which the combined capacity of hydro, wind, solar and biomass increases by more than 60% over the next five years. Even in its "base case," renewable capacity is set to expand by nearly 50%, the IEA forecasts.
Dr. Fatih Birol, IEA executive director, writes in a foreword to the report that "thanks to falling costs, technologies such as solar photovoltaics (PV) and wind are at the heart of transformations taking place across the global energy system." He adds: "Their increasing deployment is crucial for efforts to tackle greenhouse gas emissions, reduce air pollution and expand energy access."
The IEA's base-case renewable forecasts have historically underestimated the pace of growth. Yet even in its accelerated case, the extra electricity from renewable sources will fail to keep up with rising overall demand, the IEA forecasts suggest.
This means that generation from fossil fuels would also have to increase, along with the electricity sector's CO2 emissions, rather than falling rapidly as required to meet global climate goals.
Rapid Growth
In its base case, the newly published 2019 IEA report forecasts that global renewable energy capacity will increase by close to 50% in the five years to 2024, as the chart below shows (red line).
This would mean global hydro, wind, solar and biomass capacity rising from 2,501 gigawatts (GW) in 2018 to 3,721GW in 2024. The increase of 1,220GW means the world would be building renewable capacity equal to the entire U.S. electricity system today, says the IEA.
Global renewable energy capacity, gigawatts, between 2010 and 2018 (black line) and IEA forecasts for five years ahead published in each year between 2013 and 2018 (shades of blue). Forecasts for 2019 are shown in red (base case) and dashed-red lines (accelerated case). Source: IEA Renewables 2019 report and previous iterations. Chart by Carbon Brief using Highcharts.
Within the base case total, wind and solar capacity would nearly double, contributing around 85% of the increase for all renewables, with hydro accounting for another tenth and bioenergy 4%.
It is worth noting, however, that the IEA's base-case has historically underestimated the pace of growth, as the chart above shows. As a result, successive forecasts have been revised upwards in light of increasingly favorable policy conditions and faster-than-expected reductions in cost.
In a series of auctions tracked by the IEA, the cost of solar has fallen from $160 per megawatt hour (MWh) in 2014 to an average of $17/MWh for projects due to start operating in 2023, while for onshore wind the costs have fallen from $65/MWh in 2014 to $30/MWh for 2023.
The IEA has also included an "accelerated case" in its 2019 forecasts, shown with a dashed line in the chart, above. In this case, renewable capacity would increase by more than 60% to 4,036GW in 2024, adding 1,535GW in five years, equivalent to the current total fleets of the U.S. and Japan.
This is not the first time that the IEA has hedged its view for the next five years.
Back in 2016, for example, the agency's base case forecast some 826GW of renewable capacity being added by 2021, with an accelerated case adding 1,061GW. This accelerated case from 2016 aligns closely with the 2019 base case, which has 1,096GW being added during 2016-2021.
Bottom Up
The IEA forecast is based on detailed bottom-up analysis of the market, policy and electricity system outlook in each of 41 individual countries and every world region.
Capacity growth is expected to be concentrated in just a handful of regions, the IEA says, with 40% in China, 17% in Europe, 11% in the U.S. and 9% in India. Together, these account for four-fifths of the global increase in the IEA's base case.
As already mentioned, renewable capacity has consistently oustripped the growth expected in the IEA base case, which has tended to suggest that annual additions will remain at a similar level into the future, rather than consistently rising year on year.
The amount of new renewable capacity built around the world, each year since 2006, is shown in red in the chart below, while successive base-case forecasts are shown in shades of blue.
Annual renewable energy capacity additions, gigawatts, between 2006 and 2018 (red line) and IEA forecasts for growth over five years published between 2013 and 2019 (shades of blue). A 2019 "accelerated case" is shown with a dashed red line. Source: IEA Renewables 2019 report and previous iterations. Chart by Carbon Brief using Highcharts.
As in previous years, the IEA has once again raised its forecast growth over the next five years, adding 14% to the amount of new capacity that it expects to be built. Last year, it forecast growth of 1,070GW over the five years to 2023. Now, it is forecasting 1,220GW in the five years to 2024.
Responding to a question from Carbon Brief, Heymi Bahar, IEA senior renewable energy analyst and a lead author of the report told a pre-publication press call that this upwards revision was due to a roughly 50/50 combination of more favorable policy and lower costs.
On the policy side, Bahar pointed to a series of additional renewables auctions in the EU, initiated as countries look to meet their 2020 targets and as the bloc's 2030 goals have been firmed up. In China, grid expansion and market reforms have reduced the amount of renewable electricity that is "curtailed" – generation that is wasted due to insufficient grid capacity or an excess of supply.
The flattening of renewable capacity growth during 2018, seen in the red line in the chart, above, was also largely down to changes in China. This stalling marked the first time in two decades when the amount of renewable capacity built each year failed to exceed that seen before.
During 2018, China started to shift decisively away from support based on "feed-in tariffs" that pay renewables a fixed price for each unit of electricity generated and towards a system of competitive auctions awarding a fixed pot of money or capacity to the lowest bidders.
This seismic change in the policy landscape of the world's largest market for renewable energy had been widely expected to dent global growth, including in last year's IEA report. Yet as this year's figures show, despite a small dip in China itself, the global picture was buoyed by strong growth in other markets, keeping growth steady overall, rather than the expected decline.
Number One
The pace of expansion in renewable capacity has already dented the prospects of fossil-fueled sources of electricity in many countries, eating into their market share and changing the way wholesale prices vary across days, months and seasons.
Nevertheless, the growth of global electricity demand has been such that generation from fossil-fuel sources has continued to rise, increasing the sector's contribution to CO2 emissions. Moreover, coal has comfortably maintained its position as the world's largest source of electricity.
IEA executive director Dr. Birol says in a press release:
"Renewables are already the world's second largest source of electricity, but their deployment still needs to accelerate if we are to achieve long-term climate, air quality and energy access goals."
Since 2010, global supplies of renewable electricity have expanded by 60%, adding enough output to power half the U.S. economy. Yet this growth was only sufficient to cover half of the increase in global electricity demand, with the other half coming from a roughly equal split of coal and gas.
Over the next five years, the IEA base case forecasts that renewables will meet a larger two-thirds share of the increase in global demand. This would mean a continuing, if somewhat diminished role for coal and gas in meeting rising demand, with extra CO2 emissions to match.
Since the majority of demand growth would be met by renewables, they would claim an increasingly large share of the global electricity mix. In the base case, renewables (red line and dots) would increase their share from 25% today to 30% in 2024, gaining five percentage points in five years. This would largely come at the expense of coal (black), which would drop to 34% of the mix, but would remain the biggest contributor to global electricity supplies.
Change in the share of global electricity generation accounted for by coal (black lines), renewables (red), gas (blue) and nuclear (purple) between 2018 and 2024. The IEA base case is shown on the left while Carbon Brief's estimate of the mix in the IEA accelerated case is on the right. Source: IEA Renewables 2019 report and Carbon Brief analysis. Chart by Carbon Brief using Highcharts.
Given the increase in demand overall, gas in particular, but also coal, would see their output – and emissions – increasing over the next five years in the IEA base case, despite losing market share.
The IEA's report does not include equivalent figures for its "accelerated case," where renewables grow more quickly than expected. However, Carbon Brief analysis of the IEA's capacity forecasts suggests it could mean renewables matching coal as the world's joint-largest sources of electricity.
This is shown in the chart, above right, where the renewable share of global electricity supplies would reach 32% by 2024 and coal would fall to a similar level. But even in this accelerated case, renewables would meet only 80% of the increase in demand, with gas making up the remainder.
This accelerated case for renewables could mean coal output flattening or even starting to decline out to 2024, but not at the rate required to get onto a pathway compatible with global climate goals.
As in previous years, the IEA sets out three areas that would need to be addressed in order for the accelerated case to be realized. These are: policy and regulatory uncertainty; high investment risks in developing countries; and managing the integration of variable renewables into existing grids.
(The IEA notes that in the early stages of wind and solar deployment curves in each country or region, "integration challenges are often not as serious as anticipated.")
The integration issue is a particular concern for "distributed" solar, the IEA suggests. This includes residential rooftops, but also larger commercial and industrial rooftop systems, which tend to have lower costs, the IEA says.
Given costs for these systems are now at or below the price of retail electricity in most countries – with costs set to fall a further 15-35% by 204 – there is an "explosive cocktail" of ingredients is in place for a "boom" in distributed solar capacity, Paolo Frankl, head of the IEA's renewable energy division told a pre-publication press call.
Dr. Birol told the call that this sector had "breathtaking" potential, but would need to be carefully managed so as to balance the interests of distributed solar owners, other consumers and the companies that manage electricity grids.
U.S. #RenewableEnergy Capacity Beats #Coal for the First Time https://t.co/uDrqOER2z9 @BeyondCoal @RenewablesNews
— EcoWatch (@EcoWatch) June 17, 2019
Reposted with permission from our media associate Carbon Brief.
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This is the first-ever quarter where renewables outpaced fossil fuels since the UK's first public electricity generating station opened in 1882. It is another symbolic milestone in the stunning transformation of the UK's electricity system over the past decade.
Nevertheless, a lack of progress in other parts of the economy means the UK remains far off track against its upcoming legally-binding carbon targets, let alone the recently adopted goal of net-zero greenhouse gas emissions by 2050.
Transformative Decade
At the start of this decade in 2010, the 288TWh generated from fossil fuels accounted for around three-quarters of the UK total. It was also more than 10 times as much electricity as the 26TWh that came from renewables.
Since then, electricity generation from renewable sources has more than quadrupled – and demand has fallen – leaving fossil fuels with a shrinking share of the total.
This shift is shown in the chart below, with the declining quarterly output from power stations burning coal, oil and gas in blue and rising generation from renewables in red.
(The quarterly chart also reflects the seasons, with demand higher in winter and lower in summer. Wind farm output is well matched with this cycle, as it tends to be windier in winter.)
Quarterly electricity generation in the UK between 2009 and the third quarter of 2019, in terawatt hours, with fossil-fuel output shown with a blue line (coal, oil and gas) and renewables shown in red (wind, biomass, solar and hydro). Source: BEIS Energy Trends and Carbon Brief analysis of data from BM Reports. Chart by Carbon Brief using Highcharts
The chart above shows that electricity generation from fossil fuels has halved since 2010, from 288TWh down to 142TWh in the most recent 12-month period.
Gas now contributes the vast majority of that shrinking total, as coal plants close down ahead of a planned phaseout in 2025. These ageing power stations were mostly built in the 1960s and 70s and are increasingly uneconomic to run due to CO2 prices, market forces and pollution rules.
In the third quarter of 2019, some 39 percent of UK electricity generation was from coal, oil and gas, including 38% from gas and less than 1 percent from coal and oil combined.
Another 40 percent came from renewables, including 20 percent from wind, 12 percent from biomass and 6 percent from solar. Nuclear contributed most of the remainder, generating 19 percent of the total.
While it is unlikely that renewables will generate more electricity than fossil fuels during the full year of 2019, it is now a question of when – rather than if – this further milestone will be passed.
This summer, National Grid predicted that zero-carbon sources of electricity – wind, nuclear, solar and hydro, but not biomass – would generate more electricity than fossil fuels during 2019. Carbon Brief's analysis through to the third quarter of the year is in line with this forecast.
New Capacity
Over the past year, the most significant reason for rising renewable generation has been an increase in capacity as new offshore wind farms have opened. The 1,200 megawatt (MW) Hornsea One project was completed in October, becoming the world's largest offshore wind farm. The 588MW Beatrice offshore wind farm was completed in Q2 of this year.
These schemes add to the more than 2,100MW of offshore capacity that started operating during 2018. Further capacity is already being built, including the 714MW East Anglia One project that started generating electricity this year and will be completed in 2020.
In total, government contracts for offshore wind will take capacity from nearly 8,500MW today to around 20,000MW by the mid-2020s. The government and industry are jointly aiming for at least 30,000MW of offshore wind capacity by 2030, with two further contract auctions already expected.
In September, the latest auction round produced record-low deals for offshore wind farms that will generate electricity more cheaply than expected market prices – and potentially below the cost of running existing gas plants.
Other contributors to the recent increase in renewable generation include the opening of the 420MW Lynemouth biomass plant in Northumberland last year and the addition of hundreds of megawatts of new onshore wind and solar farms. (Another new 299MW biomass plant being built on Teesside, with a scheduled opening in early 2020, is facing "major delays".)
According to the Department of Business, Energy and Industrial Strategy (BEIS), the rise in renewable output during the first half of 2019 was down to these increases in capacity, with weather conditions not unusual for the time of year.
Some two-thirds of electricity generated from biomass in the UK comes from "plant biomass", primarily wood pellets burnt at Lynemouth and the Drax plant in Yorkshire. The remainder comes from an array of smaller sites based on landfill gas, sewage gas or anaerobic digestion.
The Committee on Climate Change says the UK should "move away" from large-scale biomass power plants, once existing subsidy contracts for Drax and Lynemouth expire in 2027.
Using biomass to generate electricity is not zero-carbon and in some circumstances could lead to higher emissions than from fossil fuels. Moreover, there are more valuable uses for the world's limited supply of biomass feedstock, the CCC says, including carbon sequestration and hard-to-abate sectors with few alternatives.
In terms of fossil-fuel generating capacity, the UK's remaining coal plants are rapidly closing down, well ahead of a 2025 deadline to phase out unabated burning of the fuel. By March 2020, just four coal plants will remain in the UK.
Utility firms have plans to build up to 30,000MW of new gas capacity – including 3,600MW at Drax recently given government planning approval – despite the fact that government projections suggest only around 6,000MW might be needed by 2035.
It is unlikely that all of the planned new gas capacity will get built. The schemes are generally reliant on winning contracts under the UK's capacity market, which is designed to ensure electricity supply is always sufficient to meet demand.
The rise of renewables means that gas generation is likely to continue falling in the UK, whether or not this new capacity gets built. Nevertheless, the UK is unlikely to meet its legally binding goal of cutting overall emissions to net-zero by 2050, unless progress in the electricity sector is matched by reductions in other parts of the UK economy, such as heating and transport.
Consecutive Months
Carbon Brief's electricity-sector analysis shows that renewables are also estimated to have generated more electricity than fossil fuels during the individual months of August and September, the first time there have been two consecutive such months.
Previously, renewables beat fossil fuels in September 2018 – the first-ever whole month – and then again in March 2019. This means that there have only ever been four months where renewables outpaced fossil generation, of which three have been this year and two in the last two months.
This is shown in the chart, below, which also highlights the greater month-to-month variability in electricity generation and demand, which is overlaid on top of the broader seasonal cycles.
Monthly electricity generation in the UK between 2012 and the third quarter of 2019, in terawatt hours, with fossil-fuel output shown with a blue line (coal, oil and gas) and renewables shown in red (wind, biomass, solar and hydro). Source: Carbon Brief analysis of data from BEIS Energy Trends and BM Reports. Chart by Carbon Brief using Highcharts
In the first three quarters of 2019, renewables outpaced fossil fuels on 103 of the 273 individual days, Carbon Brief analysis suggests. This is more than one-third of the days in the year so far and includes 40 of the 91 days in the third quarter of 2019.
(Although this is not a majority of days, the aggregate output during the quarter was higher for renewables. This is because their excess over fossil fuels was large on some days.)
As expected from the monthly aggregates in the chart, above, these days with higher renewable generation are concentrated in March and the third quarter of 2019, as shown in the chart, below.
Daily electricity generation in the UK during the first three quarters of 2019, in terawatt hours, with fossil-fuel output shown with a blue line (coal, oil and gas) and renewables shown in red (wind, biomass, solar and hydro). Source: Carbon Brief analysis of data from BEIS Energy Trends and BM Reports. Chart by Carbon Brief using Highcharts.
The total of 103 days with higher renewable electricity generation than from fossil fuels in the first three quarters of the year is far in excess of the 67 such days by the same point in 2018.
This is shown in the chart, below, which also highlights the fact that there had never been any days with higher renewable generation until 2015.
Cumulative count of days each year when electricity generation from renewables was higher than that from fossil fuels. Prior to 2015 there were no days when renewables outpaced fossil fuels. Source: Carbon Brief analysis of data from BEIS Energy Trends and BM Reports. Chart by Carbon Brief using Highcharts.
There have already been nearly as many higher renewable days in the first three quarters of 2019, at 103, as there were in the whole of 2018, which saw 107 such days. There were only 58 such days in 2017, just 16 in 2016 and 12 in 2015. The first ever day when UK renewables generated more electricity than fossil fuels was 11 April 2015.
Methodology
The figures in the article are from Carbon Brief analysis of data from BEIS Energy Trends chapter 5 and chapter 6, as well as from BM Reports. The figures from BM Reports are for electricity supplied to the grid in Great Britain only and are adjusted to include Northern Ireland.
In Carbon Brief's analysis, the BM Reports numbers are also adjusted to account for electricity used by power plants on site and for generation by plants not connected to the high-voltage national grid. This includes many onshore wind farms, as well as industrial gas combined heat and power plants and those burning landfill gas, waste or sewage gas.
By design, the Carbon Brief analysis is intended to align as closely as possible to the official government figures on electricity generated in the UK, reported in BEIS Energy Trends table 5.1. Briefly, the raw data for each fuel is adjusted with a multiplier, derived from the ratio between the reported BEIS numbers and unadjusted figures for previous quarters.
Carbon Brief's method of analysis has been verified against published BEIS figures using "hindcasting". This shows the estimates for total electricity generation from fossil fuels or renewables to have been within ±3% of the BEIS number in each quarter since Q4 2017. (Data before then is not sufficient to carry out the Carbon Brief analysis.)
For example, in the second quarter of 2019, a Carbon Brief hindcast estimates gas generation at 33.1TWh, whereas the published BEIS figure was 34.0TWh. Similarly, it produces an estimate of 27.4TWh for renewables, against a BEIS figure of 27.1TWh.
The Carbon Brief estimated totals for fossil fuels and renewables are very close in Q3 2019, coming within 0.5TWh of each other. This means that despite the relatively low level of uncertainty in the estimates, their relative position could be reversed in the official BEIS data.
This serves to emphasize the fact that the broader trend of decline for fossil fuels and an increase for renewables is of far greater significance than the precise figures for any individual quarter.
In contrast to Carbon Brief's analysis, figures published by consultancy EnAppSys for the third quarter of 2019 suggest that fossil fuels generated slightly more electricity than renewables. There are several reasons for this difference.
First, the company's analysis is for Great Britain only, whereas Carbon Brief's covers the UK overall. Second, it reports on electricity "supplied" in the country, including imports, whereas Carbon Brief estimates the amount of electricity "generated" within the UK only.
Third, Carbon Brief's analysis is, by design, aligned with the quarterly BEIS Energy Trends data for electricity generation, whereas EnAppSys uses its own approach.
For comparison, EnAppSys reported for the second quarter of 2019 that 28.3TWh was supplied in GB from gas, whereas BEIS reports that 34.0TWh was generated in the UK. Similarly EnAppSys reported 23.1TWh coming from renewables, against a BEIS figure of 27.1TWh.
Reposted with permission from our media associate Carbon Brief.
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Projects in every city analyzed by the researchers could be built today without subsidy, at lower prices than those supplied by the grid, and around a fifth could also compete with the nation's coal electricity prices.
They say grid parity – the "tipping point" at which solar generation costs the same as electricity from the grid – represents a key stage in the expansion of renewable energy sources.
While previous studies of nations such as Germany and the U.S. have concluded that solar could achieve grid parity by 2020 in most developed countries, some have suggested China would have to wait decades.
However, the new paper published in Nature Energy concludes a combination of technological advances, cost declines and government support has helped make grid parity a reality in Chinese today.
Despite these results, grid parity may not drive a surge in the uptake of solar, a leading analyst tells Carbon Brief.
Competitive Pricing
China's solar industry has rapidly expanded from a small, rural program in the 1990s to the largest in the world. It is both the biggest generator of solar power and the biggest installer of solar panels.
The installed capacity of solar panels in China in 2018 amounted to more than a third of the global total, with the country accounting for half the world's solar additions that year.
Since 2000, the Chinese government has unveiled over 100 policies supporting the PV industry, and technological progress has helped make solar power less expensive. This has led to the cost of electricity from solar power dropping, as demonstrated in the chart below.
Chart showing the historical levelized cost of electricity (LCOE) from solar power in China.
Source: Yan et al. (2019)
In their paper, professor Jinyue Yan of Sweden's Royal Institute of Technology and his colleagues explain that this "stunning" performance has been accelerated by government subsidies, but has also seen China overinvesting in "redundant construction and overcapacity." The authors write:
"Recently, the Chinese government has been trying to lead the PV industry onto a more sustainable and efficient development track by tightening incentive policies with China's 531 New Policy."
The researchers say the subsidy cuts under this policy in 2018 were a signal that the government wanted to make the industry less dependent on state support and shift its focus from scale to quality.
This, they say, has "brought the industry to a crossroads," with discussions taking place in China about when solar electricity generation could achieve grid parity.
In their analysis, Yan and his team examined the prospects for building industrial and commercial solar projects without state support in 344 cities across China, attempting to gauge where or whether grid parity could be achieved.
The team estimated the total lifetime price of solar energy systems in all of these cities, taking into account net costs and profits, including project investments, electricity output and trading prices.
Besides establishing that installations in every city tested could supply cheaper electricity than the grid, they also compared solar to the price of coal-generated power. They found that 22% of the cities could build solar systems capable of producing electricity at cheaper prices than coal.
Embracing Solar
Declining costs of solar technology, particularly crystalline silicon modules, mean the trend in China is also playing out around the world. In May, the International Renewable Energy Agency (IRENA) said that by the beginning of next year, grid parity could become the global norm for the solar industry.
Kingsmill Bond, an energy strategist at Carbon Tracker, says this is the first in-depth study he has seen looking at city-level solar costs in China, and is encouraged by this indication of solar becoming ever-more competitive. He tells Carbon Brief:
"The conclusion that industrial and commercial solar is cheaper than grid electricity means that the workshop of the world can embrace solar. Without subsidy and its distorting impacts, and driven by commercial gain."
On the other hand, Jenny Chase, head of solar analysis at BloombergNEF, says the findings revealed by Yan and his team are "fairly old news" as the competitive price of rooftop solar in China has been known about for at least a year.
She notes that this does not mean there has been a huge accompanying rollout of industrial and commercial solar, and says this is partly because of the long-term thinking required for investment to be seen as worthwhile.
#China leading on world’s clean #energy investment, says report: https://t.co/shGL9Sk7hg #ClimateAction RT @EcoWatch pic.twitter.com/lQoBJZgc6I
— Connect4Climate (@Connect4Climate) January 12, 2018
Reposted with permission from our media associate Carbon Brief.
The research, published Monday in Nature Communications, is the first to explore the use of direct air capture (DAC) in multiple computer models. It shows that a "massive" and energy-intensive rollout of the technology could cut the cost of limiting warming to 1.5 or 2 C above pre-industrial levels.
But the study also highlights the "clear risks" of assuming that DAC will be available at scale, with global temperature goals being breached by up to 0.8 C if the technology then fails to deliver.
This means policymakers should not see DAC as a "panacea" that can replace immediate efforts to cut emissions, one of the study authors tells Carbon Brief, adding: "The risks of that are too high."
DAC should be seen as a "backstop for challenging abatement" where cutting emissions is too complex or too costly, says the chief executive of a startup developing the technology. He tells Carbon Brief that his firm nevertheless will "continuously push back on the 'magic bullet' headlines."
Negative Emissions
The 2015 Paris agreement set a goal of limiting human-caused warming to "well below" 2 C and an ambition of staying below 1.5 C. Meeting this ambition will require the use of "negative emissions technologies" to remove excess CO2 from the atmosphere, according to the Intergovernmental Panel on Climate Change (IPCC).
This catch-all term covers a wide range of approaches, including planting trees, restoring peatlands and other "natural climate solutions." However, model pathways developed by researchers rely most heavily on bioenergy with carbon capture and storage (BECCS). This is where biomass, such as wood pellets, is burned to generate electricity and the resulting CO2 is captured and stored.
The significant potential role for BECCS raises a number of concerns, with land areas up to five times the size of India devoted to growing the biomass needed in some model pathways.
One alternative is direct air capture, where machines are used to suck CO2 out of the atmosphere. If the CO2 is then buried underground, the process is sometimes referred to as direct air carbon capture and storage (DACCS).
The new study explores how DAC could help meet global climate goals with "lower costs," using two different integrated assessment models (IAMs). Study author Dr. Ajay Gambhir, senior research fellow at the Grantham Institute for Climate Change at Imperial College London, explains to Carbon Brief:
"This is the first inter-model comparison … [and] has the most detailed representation of DAC so far used in IAMs. It includes two DAC technologies, with different energy inputs and cost assumptions, and a range of energy inputs including waste heat. The study uses an extensive sensitivity analysis [to test the impact of varying our assumptions]. It also includes initial analysis of the broader impacts of DAC technology development, in terms of material, land and water use."
The two DAC technologies included in the study are based on different ways to adsorb CO2 from the air, which are being developed by a number of startup companies around the world.
One, typically used in larger industrial-scale facilities such as those being piloted by Canadian firm Carbon Engineering, uses a solution of hydroxide to capture CO2. This mixture must then be heated to high temperatures to release the CO2 so it can be stored and the hydroxide reused. The process uses existing technology and is currently thought to have the lower cost of the two alternatives.
The second technology uses amine adsorbents in small, modular reactors such as those being developed by Swiss firm Climeworks. Costs are currently higher, but the potential for savings is thought to be greater, the paper suggests. This is due to the modular design that could be made on an industrial production line, along with lower temperatures needed to release CO2 for storage, meaning waste heat could be used.
Delayed Cuts
Overall, despite "huge uncertainty" around the cost of DAC, the study suggests its use could allow early cuts in global greenhouse gas emissions to be somewhat delayed, "significantly reduc[ing] climate policy costs" to meet stringent temperature limits.
Using DAC means that global emissions in 2030 could remain at higher levels, the study says, with much larger use of negative emissions later in the century. This is shown in the charts, below, for scenarios staying below 1.5 C (left panel, shades of blue) and 2 C (right, green).
Pathways without DAC are shown in darker shades. For example, the solid dark blue line shows results from the "TIAM" model, with emissions peaking around 2020 and falling rapidly to below zero around 2050.
In contrast, the light blue solid line shows a pathway where DAC allows a more gradual decline, reaching zero in the 2060s and with negative emissions of around 30 billion tonnes per year (Gt/yr) by the 2080s. This is close to today's annual global emissions of around 40GtCO2/yr.
Global CO2 emissions from fossil fuels (Gt/yr) in model pathways consistent with limiting warming this century to 1.5 C (left panel, blue) or 2 C (right panel, green). Results from two different IAMs – TIAM and WITCH – are shown with solid and dashed lines, respectively. The various lines show scenarios that use direct capture ("DAC," darker shades) and those that do not ("NoDAC," lighter), as well as pathways to 2 C without negative emissions of any sort ("NoNET," darkest green). Source: Realmonte et al. (2019).
"The results of both models are surprisingly similar," says Dr. Nico Bauer, a scientist at the Potsdam Institute for Climate Impacts Research (PIK), who was not involved in the study. He tells Carbon Brief: "This increases the credibility about the main conclusions that the DACCS technology can play an important role in a long-term climate change mitigation strategy."
The use of DAC in some of the modeled pathways delays the need to cut emissions in certain areas. The paper explains: "DACCS allows a reduction in near term mitigation effort in some energy-intensive sectors that are difficult to decarbonise, such as transport and industry."
Steve Oldham, chief executive of DAC startup Carbon Engineering says he sees this as the key purpose of CO2 removal technologies, which he likens to other "essential infrastructure" such as waste disposal or sewage treatment.
Oldham tells Carbon Brief that while standard approaches to cutting CO2 remain essential for the majority of global emissions, the challenge and cost may prove too great in some sectors. He says:
"DAC and other negative emissions technologies are the right solution once the cost and feasibility becomes too great … I see us as the backstop for challenging abatement."
Comparing Costs
Even though DAC may be relatively expensive, the model pathways in the new study still see it as much cheaper than cutting emissions from these hard-to tackle sectors. This means the models deploy large amounts of DAC, even if its costs are at the high end of current estimates.
It also means the models see pathways to meeting climate goals that include DAC as having lower costs overall ("reduce[d]… by between 60 to more than 90%").
Gambhir tells Carbon Brief: "Deploying DAC means less of a steep mitigation pathway in the near-term, and lowers policy costs, according to the modeled scenarios we use in this study."
However, the paper also points to the significant challenges associated with such a large-scale, rapid deployment of DAC, in terms of energy use and the need for raw materials.
The energy needed to run direct air capture machines in 2100 is up to 300 exajoules each year, according to the paper. This is more than half of overall global demand today, from all sources, and despite rising demand this century, it would still be a quarter of expected demand in 2100.
To put it another way, it would be equivalent to the current annual energy demand of China, the U.S., the EU and Japan combined – or the global supply of energy from coal and gas in 2018.
Gambhir tells Carbon Brief:
"Large-scale deployment of DAC in below-2°C scenarios will require a lot of heat and electricity and a major manufacturing effort for production of CO2 sorbent. Although DAC will use less resources such as water and land than other NETs [such as BECCS], a proper full life-cycle assessment needs to be carried out to understand all resource implications."
Deployment Risk
There are also questions as to whether this new technology could be rolled out at the speed and scale envisaged, with expansion at up to 30% each year and deployment reaching 30GtCO2/yr towards the end of the century. This is a "huge pace and scale," Gambhir says, with the rate of deployment being a "key sensitivity" in the study results.
Professor Jennifer Wilcox, professor of chemical engineering at Worcester Polytechnic Institute, who was not involved with the research, says that this rate of scale-up warrants caution. She tells Carbon Brief:
"Is the rate of scale-up even feasible? Typical rules of thumb are increase by an order of magnitude per decade [growth of around 25-30% per year]. [Solar] PV scale-up was higher than this, but mostly due to government incentives … rather than technological advances."
Reaching 30GtCO2/yr of CO2 capture – a similar scale to current global emissions – would mean building some 30,000 large-scale DAC factories, the paper says. For comparison, there are fewer than 10,000 coal-fired power stations in the world today.
If DAC were to be carried out using small modular systems, then as many as 30m might be needed by 2100, the paper says. It compares this number to the 73m light vehicles that are built each year.
The study argues that expanding DAC at such a rapid rate is comparable to the speed with which newer electricity generation technologies such as nuclear, wind and solar have been deployed.
Climeworks greenhouse © Climeworks / Julia Dunlop
The modeled rate of DAC growth is "breathtaking" but "not in contradiction with the historical experience," Bauer says. This rapid scale-up is also far from the only barrier to DAC adoption.
The paper explains: "[P]olicy instruments and financial incentives supporting negative emission technologies are almost absent at the global scale, though essential to make NET deployment attractive."
Carbon Engineering's Oldham agrees that there is a need for policy to recognize negative emissions as unique and different from standard mitigation. But he tells Carbon Brief that he remains "very very confident" in his company's ability to scale up rapidly.
(The new study includes consideration of the space available to store CO2 underground, finding this not to be a limiting factor for DAC deployment.)
Breaching Limits
The paper says that the challenges to scale-up and deployment on a huge scale bring significant risks, if DAC does not deliver as anticipated in the models. Committing to ramping up DAC rather than cutting emissions could mean locking the energy system into fossil fuels, the authors warn.
This could risk breaching the Paris temperature limits, the study explains:
"The risk of assuming that DACCS can be deployed at scale, and finding it to be subsequently unavailable, leads to a global temperature overshoot of up to 0.8°C."
Gambhir says the risks of such an approach are "too high":
"Inappropriate interpretations [of our findings] would be that DAC is a panacea and that we should ease near-term mitigation efforts because we can use it later in the century."
Bauer agrees:
"Policymakers should not make the mistake to believe that carbon removals could ever neutralise all future emissions that could be produced from fossil fuels that are still underground. Even under pessimistic assumptions about fossil fuel availability, carbon removal cannot and will not fix the problem. There is simply too much low-cost fossil carbon that we could burn."
Nonetheless, professor Massimo Tavoni, one of the paper's authors and the director of the European Institute on Economics and the Environment (EIEE), tells Carbon Brief that "it is still important to show the potential of DAC – which the models certainly highlight – but also the many challenges of deploying at the scale required."
The global carbon cycle poses one final – and underappreciated – challenge to the large-scale use of negative emissions technologies such as DAC: ocean rebound. This is because the amount of CO2 in the world's oceans and atmosphere is in a dynamic and constantly shifting equilibrium.
This equilibrium means that, at present, oceans absorb a significant proportion of human-caused CO2 emissions each year, reducing the amount staying in the atmosphere. If DAC is used to turn global emissions net-negative, as in the new study, then that equilibrium will also go into reverse.
As a result, the paper says as much as a fifth of the CO2 removed using DAC or other negative emissions technologies could be offset by the oceans releasing CO2 back into the atmosphere, reducing their supposed efficacy.
"We are in deep trouble." In my 2nd @EcoWatch post today, the latest @IEA data shows energy-related C02 emissions hit a record high in 2018: https://t.co/yESL234Q8j
— Olivia Rosane (@orosane) March 26, 2019
Reposted with permission from our media associate Carbon Brief.
Scientists have relatively low confidence in detecting a link between tornado activity and climate change. They cannot exclude the possibility of a link; rather, the science is so uncertain that they simply do not know at this point.
What is clear is that there is no observable increase in the number of strong tornadoes in the U.S. over the past few decades. At the same time, tornadoes have become more clustered, with outbreaks of multiple tornadoes becoming more common even as the overall number has remained unchanged. There is also evidence that tornado "power" has been increasing in recent years.
Some research has suggested that climate change will create conditions more favorable to the formation of severe thunderstorms and tornadoes, but such effects are not detectable in observations today.
Any role for climate change in affecting the conditions for tornado formation is still very much an open question and the subject of ongoing research by the scientific community.
Highly Uncertain Attribution
Climate change affects different extreme weather events in different ways. Some, such as increases in extreme heat events, reductions in extreme cold events, and increases in extreme precipitation events are easy to understand and attribute to a changing climate. Others, such as the severe convective storms that produce tornadoes, are much more difficult to unpick.
The figure below shows how well the effects of climate change on different extreme events are understood. It ranks each type of extreme event based on how well the effects of climate change are understood (the x-axis) and on the extent to which any individual event can be attributed to climate change (the y-axis).
Understanding and attribution of climate change impacts on extreme events, by event type.
Figure from the U.S. National Academy of Sciences report on the Attribution of Extreme Weather Events published in 2016.
According to this ranking, severe convective storms that produce tornadoes have both the least well understood link to climate change and the lowest confidence in attributing any individual storm (or tornado) to climate change.
This does not mean that there is definitively no climate link.
Dr. Marshall Shepherd, a professor at the University of Georgia and an author of the NAS report, explains in a recent column in Forbes:
"It is important to point out that just because an event is low on the scale, that doesn't mean there is no climate change influence; it simply means scientific evidence is not strong enough at this time to draw stronger conclusions."
As the NAS report points out, there is a much clearer climate link with extreme rainfall. Extreme rainfall has already increased over much of the central U.S., potentially contributing to ongoing devastating flooding in the region this year.
The 2018 Fourth National Climate Assessment has similar reservations about any links between climate change and tornadoes. It says:
"Observed and projected future increases in certain types of extreme weather, such as heavy rainfall and extreme heat, can be directly linked to a warmer world. Other types of extreme weather, such as tornadoes, hail, and thunderstorms, are also exhibiting changes that may be related to climate change, but scientific understanding is not yet detailed enough to confidently project the direction and magnitude of future change."
Some of the year-to-year variability in tornado numbers is influenced by El Niño and La Niña conditions. A 2017 paper found there are more U.S. tornadoes in La Niña years; however, the current large outbreak is during an El Niño year.
Other types of natural variability can affect tornado occurrence. For example, research has suggested that the "Madden-Julian oscillation," a periodic swing in temperature and moisture starting in the Indian Ocean, can have a large impact on tornado activity in the U.S. Based on this insight, scientists predicted in late April that there would be a high likelihood of tornadoes in late May.
U.S. tornado tracks by Fujito scale severity (F0-F5) from 1950-2016.
Image from usatornadoes.com.
While the overall number of reported tornadoes in the U.S. has doubled since the 1950s, this statistic is highly misleading. Until the 1990s, tornado records were mostly based on someone spotting a tornado and reporting it to the National Weather Service.
As most tornadoes are small and last only a few minutes, the number observed and reported will be considerably smaller than the true number that occurred. The increase in tornadoes over time is largely due to the advent of modern "Doppler" weather radar systems in the 1990s, which can detect weak tornadoes and those in sparsely populated areas that may previously have gone unreported.
If weak tornadoes are excluded, there is no detectable trend in tornadoes over the past century. The figure below, based on an analysis of reports in NOAA's Severe Weather Data Inventory by Carbon Brief, shows the total number of tornadoes in each year, excluding small F0 (or EF0) tornadoes that would likely have been underreported in the past.
Number of notable (F1+ or EF1+) tornadoes per year between 1950 and 2018. Data from NOAA's Severe Weather Data Inventory. Chart by Carbon Brief using Highcharts.
If only the strongest tornadoes are considered (F3-F5 or EF3-EF5), there is even weak evidence of a decline in numbers over the past few decades. However, experts warn against reading too much into an apparent decline in the number of severe tornadoes. They point out that the rating of strong tornadoes has not been consistent and that "early official records systematically rated tornadoes stronger" than those in the past three decades.
More Tornado Clusters
While there is little evidence of an increase in the number of tornadoes, there is evidence that the pattern of tornado occurrence has been changing. A 2014 study in Science found that there has been considerably more clustering of tornadoes in recent decades. In other words, there are more days in which multiple tornadoes occur, but fewer overall days with tornadoes.
The number of days each year with at least one tornado has declined in recent decades, as the chart below shows in black. At the same time, days with more than 30 tornadoes are becoming more frequent (grey).
Number of days with at least one F1+ tornado (black) and over 30 F1+ tornadoes (grey) between 1950 and 2014.
Figure 4 in Brooks et al 2014.
The authors suggest that this trend is robust, but do not have a good explanation as to why it is occurring. They cannot identify any reason why this behavior would be driven by observed climate changes, but at the same time say they cannot exclude climate change as a factor.
Other recent research suggests that overall tornado "power" has increased in recent years, once all other environmental variables are accounted for. A 2018 paper by Dr. James Elsner and colleagues found a clear upward trend in tornado power of 5.5% per year over the past few decades. However, they caution that "a majority of the trend is not attributable to changes in storm environments."
More Common Conditions for Tornadoes?
There is limited evidence that tornadoes have become more frequent in recent years. However, a number of climate modeling studies have suggested that conditions favoring the development of severe thunderstorms — and tornadoes — in the U.S. should become more common in the future.
As the Fourth National Climate Assessment reported:
Modeling studies consistently suggest that the frequency and intensity of severe thunderstorms in the U.S. could increase as climate changes, particularly over the U.S. Midwest and Southern Great Plains during spring. There is some indication that the atmosphere will become more conducive to severe thunderstorm formation and increased intensity, but confidence in the model projections is low. Similarly, there is only low confidence in observations that storms have already become stronger or more frequent. Much of the lack of confidence comes from the difficulty in both monitoring and modeling small-scale and short-lived phenomena.
A 2013 paper by Dr. Noah Diffenbaugh and colleagues examined how the conditions needed for severe thunderstorms and tornadoes to develop are projected to change in climate models.
Climate models are too coarse to model individual tornadoes. However, they show a strong increase in conditions favoring severe thunderstorms over the eastern U.S. during spring and autumn months, particularly once global warming exceeds 2°C above preindustrial levels.
Dr. Jennifer Francis at Woods Hole Research Center in Massachusetts has argued that changes in Arctic sea ice have made ridge patterns in the jet stream more common. In addition, she says that this configuration of the jet stream has played a large role in the current tornado outbreak.
Other researchers have been more skeptical of the role of changing Arctic conditions in current weather patterns and stress that this is still an area of vigorous scientific debate.
While scientists cannot exclude a role for climate change in changes in tornado activity, links between the two are still largely speculative, particularly for individual events such as the recent outbreak in the U.S. As Diffenbaugh recently told The New York Times:
"Tornadoes are the kind of extreme event where we have the least confidence in our ability to attribute the odds or characteristics of individual events to an influence of global warming."
Our thoughts are with everyone impacted by the devastating tornadoes across the U.S. this past week. 💚 https://t.co/iHmmXc8KbN
— Greenpeace USA (@greenpeaceusa) May 28, 2019
Reposted with permission from our media associate Carbon Brief.
Rail is among the most efficient and lowest emitting modes of transport, according to the IEA's new report focusing on the opportunities it offers for energy and the environment.
In particular, urban and high-speed rail hold "major promise to unlock substantial benefits," the report says, which include reducing greenhouse gas emissions, congestion and air pollution.
In a foreword to the report, Dr. Fatih Birol, the IEA's executive director, argues rail transport is "often neglected" in public debates about future transport systems. "Despite the advent of cars and airplanes, rail of all types has continued to evolve and thrive," he said.
Carbon Brief takes a look at eight key charts from the report showing the status of rail in the world today—and how it could reduce emissions in future.
Energy-Efficient Rail
Rail transport is the most electrified transport sector, the IEA said. Globally, three-quarters of rail passenger movements and half of rail freight relies on electricity.
This means it is "uniquely positioned" to take advantage of the rise of renewables in the electricity mix.
It is also the most energy-efficient means of motorized passenger transport, and is far more efficient than road freight and aviation, as the chart below shows.
Chart above: Energy intensity of different transport modes in 2017. The left-hand chart shows energy intensity of passenger transport, in tonnes of oil equivalent (toe) per million passenger km travelled. The right-hand chart shows energy intensity of freight transport, in toe per million tonne km transported. Source: IEA 2019.
Rail accounts for 8 percent of the world's motorized passenger movements and 7 percent of freight transport, yet uses just 2 percent of the world's transport energy demand, the report says.
Global rail energy demand has remained relatively constant in recent years, adds the report. Since 2000, it has fallen in the EU and Japan, increased in Russia, China and India, and stayed relatively constant in North America. Diesel freight trains account for roughly half of rail energy use, while electricity accounts for the rest.
It also acts as an "oil saver," the IEA said. If all services performed by railways were instead carried by planes, cars and trucks, transport-related greenhouse gas (GHG) emissions would be 1.2bn tonnes of CO2-equivalent (GtCO2e) per year higher, the report says. This is equivalent to the emissions of the whole of Africa.
Low-Emission Rail
As it stands, around 0.3 percent of CO2 emissions from fossil fuels come from rail, says the report (this compares to around 2 percent for global aviation). However, the emissions from trains vary widely, depending on if they are powered by diesel or electricity, as well as how that electricity is generated.
Electric trains can reduce emissions compared with diesel-powered trains, said the IEA, but only if the power generation mix is not dependent on fuels with high carbon content, such as coal. This is shown in the chart below.
Chart above: Average well-to-wheel (WTW) carbon intensities for diesel powertrains and electric powertrains using various primary sources, in grammes of CO2e per megajoule. Source: IEA 2019.
The report notes:
"The much lower carbon intensity of rail (per passenger- or tonne-km) compared with most other modes of transport, means the rail sector already plays a key role in containing global GHG emissions. Looking forward, efficient electric motors and increasingly low-carbon power mixes could enable rail to contribute substantially to achieving zero-emission mobility from a well-to-wheel (WTW) perspective."
However, as the report notes, emissions from railway construction and maintenance must also be taken into account when assessing the capacity of rail projects to reduce greenhouse gas emissions. Railway lines—in particular, those with numerous tunnels, viaducts and bridges—use large amounts of concrete and steel.
According to the IEA, environmental life-cycle assessments show that the rail projects best able to reduce greenhouse gases (GHGs) are those that minimize the need for large amounts of steel, iron and concrete in construction; have a high passenger or freight throughput; and help to shift away from other modes of transport with even higher carbon intensities, such as car, trucks and aviation.
Regional Differences
Most rail networks are located in India, China, Japan, Europe, North America and Russia, said the IEA. Meanwhile, metro and light rail networks operate in most of the world's major cities.
Global conventional rail tracks have not significantly expanded over the past 20 years, said the IEA, but light, metro, and high-speed rail have all seen big rises, as the chart below shows.
Chart above: Track length by region from 1995-2016 for light rail (light green), metro rail (dark green), high-speed rail (dark blue) and conventional rail (light blue line). Note that conventional rail includes infrastructure used both by conventional passenger and freight rail.
The energy efficiency of trains also show large regional differences. Passenger trains are less energy efficient in the U.S. and the EU than in Asia, primarily due to lower occupancy, as the chart below shows.
Chart above: Energy intensities of passenger (left) and freight (right) rail in 2016. Source: IEA 2019.
Korea, Japan, Europe, China and Russia all have rail networks which are more than 60 percent electrified, with the highest share of track electrification being Korea at around 85 percent. North and South America, on the other hand, both have less than 5 percent rail electrification.
Global rail activity is slowly shifting towards electricity for both passenger and freight rail transport, added the IEA.
High-Speed Rail
High-speed rail lines have expanded rapidly in recent years, said the IEA. This is especially the case in China, which has seen large investment in high-speed rail lines and urban rail networks. Networks in Europe and Japan have also expanded, as the chart below shows.
Chart above: High-speed rail track length in key regions in 2010 and 2017. Source: IEA 2019.
Worldwide, around 600bn passenger km were travelled by high-speed rail in 2016, compared to around 100bn passenger km in 2000.
India is currently constructing its first high-speed line from Ahmedabad to Mumbai. Rail remains the primary transport mode in India and its rail activity is set to grow more than any other country, said the IEA.
High-speed rail is particularly important as it offers an established low-carbon alternative to short-distance flights, said the IEA. It said:
"As incomes rise, demand for passenger aviation, a mode of transport that is extremely difficult and expensive to decarbonize, will continue to grow rapidly.
"If designed with comfort and reliability as key performance criteria, high-speed rail can provide an attractive, low-emissions substitute to flying."
The overall impact on GHG emissions of a new high-speed rail line depends on many factors, such as passenger behavior and operational practices, says the report. But a new high-speed line can produce "almost immediate net CO2 benefits" by reducing air and car journeys, said the IEA.
High-speed rail lines can reduce aviation transport on the same routes by as much as 80 percent, said the IEA. The chart below shows the average change in passenger activity on selected air routes after new high-speed rail lines opened.
Chart above: Average change in passenger activity on selected air routes after high-speed rail implementation. Source: IEA 2019.
For example, as the chart shows, the opening of the Brussels-London Eurostar reduced the number of km travelled by plane on that route by around 55 percent.
Urban rail also holds substantial promise to reduce emissions, the IEA said, though this varies substantially between regions. The emissions savings from metro rail construction, for example, will depend on whether it attracts commuters who would otherwise use a car, as well as the emissions intensity of its power supply, the report adds.
Freight Expansion
Rail freight has risen steadily over the past 20 years and continues to expand in most countries, said the IEA. However, other forms of surface freight, such as trucks, are expanding faster, it adds. Most freight rail carries minerals, coal or agricultural products.
The U.S. and China each account for about a quarter of global rail freight activity and Russia about a fifth, says the report. In some countries freight train transport vastly outweighs passenger rail. In the U.S., for example, around 93 percent of kilometers travelled by train are for freight rather than passengers. Around a third of this is for the transport of coal.
Rail uses around 90% less energy than trucks per unit of freight and is the "only transport mode offering serious competition with trucks for land-based freight," said the IEA. Freight trains in Russia and China are the most energy efficient due to high loading and electrification, added the IEA.
The chart below shows the potential for new freight rail lines to reduce emissions compared to road transport. In a "high potential" case, where rail construction has low emissions, trains are efficient and low carbon, and train occupancy is high, reductions in GHG emissions are seen after just two years. However, even in a "low potential" case, GHG reductions are seen after 24 years.
Chart above: Annual life-cycle total GHG emissions, emissions savings and time needed to compensate upfront emissions from the building of a new freight train line in high, medium and low potential cases. Source: IEA 2019.
High-Rail Scenario
The IEA sets out two scenarios for rail expansion up to 2050 in its report. The emissions resulting from these two scenarios are shown in the chart below.
In the "base scenario," which assumes no significant new emphasis on rail in policymaking, annual investment in rail infrastructure increases to $330bn in 2050. The global track length of metros and high-speed rail both expand by 2.5 times. However, rail does no more worldwide than maintain its current share in activity relative to cars and air travel by 2050.
In this case, global transport emissions would continue to increase out to 2050 and beyond.
In the "high-rail" scenario, meanwhile, annual average investment reaches $770bn by 2050. The track length of high-speed rail increases by around 3.5 times, while metro tracks increase four-fold. Global passenger activity on rail is 60% higher than in the base scenario.
Significant emphasis is put on policy-making which encourages rail travel in this scenario.
First, policies are implemented to minimize the costs of rail travel by ensuring maximum rail network usage and working to remove technical barriers.
Second, efforts are made to maximize rail revenues, such as by capitalizing on the increase in value in homes and businesses due to rail expansion.
A third set of policies ensures that all forms of transport pays for their societal and environmental impacts, such as through fuel taxes and congestion charges.
In combination, these policies lead to greenhouse gases from global transport being 0.6 GtCO2e per year lower than in the base scenario, roughly the annual emissions of South Korea. This "aggressive, strategic deployment" of rail would see CO2 emissions from global transport peak in the late 2030s, said the IEA.
Achieving this scenario is an "ambitious, yet achievable undertaking," a spokesperson for the IEA tells Carbon Brief. They added:
"It would require significant and strategic investments on the part of companies working directly and indirectly in the rail sector, coordinated with ambitious policy action on the part of local and national governments."
Responding to the report, Prof. Clive Roberts, director of the Birmingham Centre for Railway Research and Education at the University of Birmingham, said the rail sector has "huge potential to embrace new energy and digital technologies." He told Carbon Brief:
"The [IEA] report comes at a time when the international railway industry needs to come together to develop a strategy to ensure the railway sector continues to retain its energy efficient status, ensuring rail contributes fully to future mobility."
Reposted with permission from our media associate Carbon Brief.