By Bob Henson
Between a record-strong El Niño and catastrophic floods, fires and drought, 2016 was a memorable year for weather and climate in North America as well as globally. What can we expect as we roll into 2017? A precise weather forecast is asking too much, but there is already a lot we can say about some key factors. Here are six developments to watch for in 2017. They're presented in rough order of increasing confidence, followed by details on each prediction.
1. Better Odds of El Niño Than La Niña, but a Neutral Pacific Still Favored
The biggest single driver of year-to-year atmospheric variations around the globe is the El Niño–Southern Oscillation (ENSO), including El Niño and its counterpart, La Niña. A year ago, it was virtually certain that the record-strong El Niño of 2015-16 would continue through at least the first few months of 2016, as it indeed did. This time around, the ENSO signal is far less clear-cut. Sea surface temperatures (SSTs) in the benchmark Niño 3.4 region of the eastern tropical Pacific have been inconclusive in recent months, hovering close to the La Niña threshold (at least -0.5 C below the seasonal average) since late July.
Figure 1. Departures from average sea surface temperature for this time of year as of mid-December show a diffuse, borderline La Niña signal across the central and eastern tropical Pacific. NOAA Climate Prediction Center
It's now become less likely that the ocean and atmosphere will commit to a well-defined La Niña event for early 2017. There's almost no telling what will happen later in the year, on the other side of the infamous "spring predictability barrier" that often separates one El Niño or La Niña event from another. One clue we do have is the unusual persistence this year of a belt of warmer-than-average SSTs from the central tropical Pacific to the west coast of North America. This warm phase of what's called the Pacific Meridional Mode may herald a new El Niño event in 2017-18, as niftily explained by Dan Vimont (University of Wisconsin Center for Climatic Research) in a recent climate.gov post.
In their joint probabilistic outlook issued in early December, NOAA's Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI) called for decreasing odds of La Niña over the next few months, dropping to just 18 percent by late spring. Neutral conditions are deemed most likely by CPC/IRI, with 65 percent odds by spring and 53 percent by summer. And the odds of El Niño are expected to steadily rise throughout the first half of 2017, reaching 29 percent by summer. Strong El Niño events like the one we just had are usually followed by a significant La Niña event. If the atmosphere instead ends up cueing El Niño for 2017-18, it would reinforce the notion that we've entered a positive phase of the Pacific Decadal Oscillation—a sign that we might expect more El Niño than La Niña events for as long as a decade or two.
Figure 2. Probabilities of El Niño (red), La Niña (blue) and neutral conditions (green), for each overlapping three-month period from November-January 2016-17 (left) to July-September 2017 (right).NOAA / IRI
2. Wide Range of Possibilities for Atlantic Hurricane Action
The well-predicted demise of the 2015-16 El Niño boosted confidence in 2016's largely successful seasonal hurricane outlooks for the Atlantic, where wind shear was down from 2015 and sea-surface temperatures saw a spike atop their long-term warming trend. (See our roundup post from Dec. 27 on global tropical cyclones in 2016 and their connections to climate change.) Because ENSO is one of the biggest shapers of Atlantic hurricane seasons, our current uncertainty about next year's ENSO state means we can't say much yet about whether the 2017 Atlantic tropical season will be hectic, sedate or somewhere in between.
Forecasters at Colorado State University no longer issue formal seasonal hurricane outlooks as early as December, but CSU's Dr. Phil Klotzbach laid out his thoughts for us last week in a qualitative discussion. Along with monitoring ENSO, Klotzbach also keeps close tabs on the Atlantic Multidecadal Oscillation and Atlantic thermohaline circulation, which are cyclic natural variations in SST, surface air pressure, and oceanic flow across the North Atlantic. When the AMO is positive (warm) and the THC is strong, the Atlantic pumps out more hurricanes over periods that can range from 25 to 35 years. At other times, unusually cold waters prevail in the far North Atlantic, typically a sign of a slowdown of the THC and a ramp-down in Atlantic hurricane action.
Figure 3. Warmer-than-average waters covered most of the Atlantic Ocean from the equator northward for the period Dec. 1-18. NOAA / ESRL Physical Sciences Division, courtesy Phil Klotzbach
With cold waters widespread across the far north Atlantic in 2014 and 2015, Klotzbach hypothesized in a 2015 Science article that the active Atlantic period that began in 1995 may have already drawn to a close. Now he's not so sure. "I was generally thinking we had moved into a cold AMO, but we haven't yet seen the re-emergence of the cold anomalies in the far North Atlantic like we have the past couple of winters (at least not yet!)," Klotzbach told me in an email. For this analysis, Klotzbach typically uses SSTs across a box roughly bounded by 50 N-60 N latitude and 10 W-50 W longitude. Figure 3 shows that only part of this area currently has below-average SSTs. "We're just now moving into the height of winter, though, so we may still see some reemergence and anomalous cooling in the far North Atlantic this winter," said Klotzbach. "I decided to hedge with the outlook so far, and hopefully we'll have a better idea of what is coming up by the time the April forecast rolls around." Here are the five possibilities (with odds) put forth by Klotzbach in his December update:
40 percent chance: AMO/THC is above average and no El Niño occurs (resulting in a seasonal average Accumulated Cyclone Energy (ACE) activity of ~ 130).
20 percent chance: AMO/THC becomes very strong in 2017 and no El Niño occurs (ACE ~ 170).
20 percent chance: AMO/THC is below average and no El Niño occurs (ACE ~ 80).
10 percent chance: AMO/THC is above average and El Niño occurs (ACE ~ 80).
10 percent chance: AMO/THC is below average and El Niño develops (ACE ~ 50).
3. More Tornadoes and Tornado Deaths in 2017 Than 2016? Probably So
It's been a blessedly quiet year for U.S. tornadoes, climatologically speaking. According to Patrick Marsh (NOAA Storm Prediction Center), the year 2016 delivered a preliminary total of 1060 tornado reports through Dec. 28, with few or none expected through the rest of the year. This may sound like a very high total, but the number of final tornado reports typically drops from the preliminary total by about 15 percent after duplicate reports have been weeded out. The annual number drops even further relative to prior years when it's adjusted for "inflation" against earlier decades, when fewer people were watching and reporting every twister. Using a linear trend adjustment, Marsh estimates that the final, inflation-adjusted tornado total for 2016 will be around 888, which would be the lowest for any year going back to at least 1954 assuming that the database is normalized (inflation-adjusted) through 2015. "Four of the last five years—2016, 2014, 2013 and 2012—have been the quietest years on record when report inflation is accounted for," said Marsh.
This year did produce a few dramatic outbreaks during peak tornado season, but these played out mostly in open country, where few structures were damaged and few people were hurt. The deadliest events of 2016 were "off-season": seven people died in a Southeast and East Coast tornado outbreak on Feb. 23-24--the nation's second-largest February outbreak on record--and five deaths occurred across the South during an overnight outbreak on Nov. 29-30.
All told, tornadoes have killed only 17 people in the U.S. in 2016, well below the average toll of 46 per year over the three prior years. Assuming we make it to Dec. 31 without any additional tornado deaths, which looks almost certain, we'll have been graced with the least-deadly U.S. year for twisters since 1986, when only 15 people were killed. In data going back to 1875 provided by Harold Brooks (National Severe Storms Laboratory), the only other year with fewer than 20 deaths was 1910, with just 12 fatalities.
Figure 5. During El Niño events (top), the frequency of U.S. tornadoes typically drops. When a La Niña phase prevails (bottom), tornado frequency goes up (indicated by red areas). The effect is strongest in the boxed area.Nature Geoscience 2015, courtesy IRI
The strong El Niño of 2015-16 likely helped tamp down tornado activity this year, at least in the heart of Tornado Alley. Researchers at IRI/Columbia University have shown that the most active spring seasons for tornado and hail over the central U.S., especially the Southern Plains, are linked to strong La Niña events, while the very quietest seasons are related to strong El Niño events. In January 2015, the researchers, led by John Allen (now at Central Michigan University), called for better-than-even odds (54 percent) of a below-average number of tornadoes this year, as opposed to the 33/33/33 percent split (below, above, and near average) one would otherwise expect. (See more details at this conference presentation).
As with Atlantic hurricanes, even a mostly quiet season can still produce deadly mayhem if one destructive event, such as a major landfalling hurricane or a family of violent tornadoes, happens to hit the wrong place at the wrong time. "It's an ongoing challenge to think about how to convey this information," Allen told me. "I think it's also worth noting that we still don't have a lot of other climate signals for improving our forecasts when we don't have ENSO-driven predictability." It's thus hard to tell how tornado counts will evolve in 2017, since the ENSO signal is so weak. However, given the very low activity this year, there's a good chance that we will see more twisters prowling the nation in 2017 than we did in 2016.
Figure 6. The U.K. Met Office predicts that the 2017 global temperature (forecast range shown in green at right) will likely fall below the record value expected to be set in 2016. The dark line shows global temperature since 1850. UK Met Office
4. A Very Warm Year Globally, but Likely Short of a Record
Barring a major, sun-blocking volcanic eruption, we can expect 2017 to continue the long-term warming trend of the last few decades attributed to human-produced greenhouse gases. However, 2017 is unlikely to continue the string of global record highs set in 2014, 2015, and (virtually certainly) 2016. The record-strong El Niño of 2015-16, which sent vast amounts of heat from ocean to atmosphere, played a key role in pushing temperatures just enough above the long-term warming trend to set new global highs. Now that this major El Niño is gone, it's no surprise that global atmospheric heat is already subsiding a bit relative to seasonal norms—though it would be a huge mistake to interpret this totally expected dip as any sign that longer-term warming has gone away.
On Dec. 20, the UK Met Office released its official outlook for 2017 (see Figure 6). The agency projects that global temperature will end up between 0.63 and 0.87 C (1.45 – 1.89 F) above the 1961-1990 average of 14.0 C (57.2 F). "This forecast, which uses the new Met Office supercomputer, adds weight to our earlier prediction that 2017 will be very warm globally but is unlikely to exceed 2015 and 2016: the two warmest years on record since 1850," said Adam Scaife, head of long-range prediction at the Met Office. According to research fellow Chris Folland: "2016 was well forecast as the methods used detected the warming influence of the strong El Niño. However, last year's El Niño only accounts for around 0.2 C of the global mean temperature rise for 2016, when compared with the long-term average between 1961 and 1990. Increasing greenhouse gases are the main cause of warming since pre-industrial times."
Figure 7. Carbon dioxide concentration (parts per million in the atmosphere) as measured atop Mauna Loa, Hawaii, in 2015 and 2016. Along with daily, weekly, and monthly variability, there is a reliable yearly cycle associated with the growth and decay of vegetation in the Northern Hemisphere.
5. Another New Peak in Global Carbon Dioxide
Sadly, our highest-confidence forecast for the atmosphere is that carbon dioxide concentrations will continue their relentless upward march. The burning of fossil fuels continues to release more than 35 billion metric tons of CO2, an invisible greenhouse gas, every year. (That's about 10,300 pounds for every person on Earth). Just over half of that total is absorbed by plants, soil and the sea each year. The rest stays in the atmosphere, much of it destined to stay there for many hundreds and even thousands of years.
CO2 values measured atop Mauna Loa Observatory in Hawaii are once again rising toward the usual spring peak after hitting their annual low in late September of around 401 parts per million. Because most of Earth's plant life is north of the equator, atmospheric CO2 drops with the growth of CO2-absorbing vegetation in late northern spring and summer, and it increases again each winter and spring as vegetation dies off. We can expect daily and weekly CO2 values in spring 2017 to soar above 410 ppm for the first time in human history, and it's even possible the monthly average will hit that mark as well.
The final weekly value below 400 ppm that we'll see in our lives is virtually certain to be the 399.86 ppm value recorded in late August 2015 during the approach of Hurricane Madeline. As that hurricane approached Hawaii from the east, its circulation is believed to have imported slightly lower-CO2 air from north of Hawaii.
Figure 8. A total solar eclipse will occur along the belt shown here on August 21, 2017. All of North America and parts of South America will experience at least a partial solar eclipse.Fred Espenak (NASA / GSFC) / MrEclipse.com
6. Slam-Dunk Forecast: A Spectacular Total Eclipse in August
We can say with rock-solid confidence that a large swath of the U.S. will be treated to one of the most widely viewable total solar eclipses in U.S. history (if the weather cooperates!) on Aug. 21. The band of totality—the region where the sun will be completely obscured by the moon for as long as 2 minutes and 40 seconds—will extend from northern Oregon across the central Plains and mid-South to South Carolina (see Figure 8). Millions of Americans will be within an hour or two's drive of the totality band, and untold numbers of people from across the world are heading to the States for the big show. The timing of totality will range from about 10 a.m. PDT on the West Coast to around 2:45 p.m. EDT on the East Coast. This means that the mid-August sun will be quite high in the sky for the eclipse, enhancing the potential drama.
NASA has a plethora of great material on the upcoming eclipse, including an excellent "Eclipse 101" page with crucial safety tips (for example, never look at an uneclipsed or partially eclipsed sun without specially designed glasses that meet international standards for eclipse viewing). Obviously, there's no telling what the weather will be doing on Aug. 21, but the perfectly named Eclipseophile website has state-by-state breakdowns of where climatology leans toward the best views. As one might expect, the highest odds of cloud-free skies and dry air are toward the western U.S.
Reposted with permission from our media associate Weather Underground.
On Thursday, April 22, the world will celebrate Earth Day, the largest non-religious holiday on the globe.
This Earth Day falls at a critical turning point. It is the second Earth Day since the start of the coronavirus pandemic and follows a year of devastating climate disasters, such as the wildfires that scorched California and the hurricanes that battered Central America. But the day's organizers still have hope, and they have chosen a theme to match.
"At the heart of Earth Day's 2021 theme, Restore Our Earth, is optimism, a critically needed sentiment in a world ravaged by both climate change and the pandemic," EarthDay.org president Kathleen Rogers told USA TODAY.
Last Earth Day marked the first time that the holiday was celebrated digitally to prevent the spread of COVID-19. This will largely be the case this year as well.
"Most of our Earth Day events will be virtual with the exception of individual and small group cleanups through our 'Great Global Cleanup' program," EarthDay.org's Olivia Altman told USA TODAY.
Tuesday, April 20: A Global Youth Summit begins at 2:30 p.m. ET featuring young climate activists like Greta Thunberg and Alexandria Villaseñor. This will be followed at 7 p.m. ET by "We Shall Breathe," a virtual summit organized by the Hip Hop Caucus to look at issues like the climate crisis, pollution and the pandemic through an environmental justice lens.
Wednesday, April 22: Beginning at 7 a.m. ET, Education International will lead the "Teach for the Planet: Global Education Summit." Talks will be offered in multiple languages and across multiple time zones to emphasize the importance of education in fighting the climate crisis.
Thursday, April 22: On the day itself, EarthDay.org will host its second ever Earth Day Live digital event beginning at 12 p.m. ET. This event will feature discussions, performances and workshops focusing on the day's theme of restoring our Earth through natural solutions, technological innovations and new ideas.
"EARTHDAY.ORG looks forward to contributing to the success of this historic climate summit and making active progress to Restore Our Earth," Rogers said in a press release. "We must see every country rapidly raise their ambition across all climate issues — and that must include climate education which would lead to a green jobs-ready workforce, a green consumer movement, and an educated and civically engaged citizenry around the world."
EarthDay.org grew out of the first Earth Day in 1970, which drew 20 million U.S. residents to call for greater environmental protections. The movement has been credited with helping to establish the U.S. Environmental Protection Agency and to pass landmark environmental legislation like the Clean Air and Water Acts. It has since gone on to be a banner day for environmental action, such as the signing of the Paris agreement in 2016. More than one billion people in more than 192 countries celebrate Earth Day each year.
This legacy continues. The organization called the scheduling of Biden's summit a "clear acknowledgement of the power of Earth Day."
"This is a critical stepping stone for the U.S. to rejoin the world in combating the climate crisis. In concert with several planned parallel EARTHDAY.ORG events worldwide, Earth Day 2021 will accelerate global action on climate change," EarthDay.org wrote.
Super-emitters are individual sources such as leaking pipelines, landfills or dairy farms that produce a disproportionate amount of planet-warming emissions, especially methane and carbon dioxide. Carbon Mapper, the non-profit leading the effort, hopes to provide a more targeted guide to reducing emissions by launching special satellites that hunt for sources of climate pollution.
"What we've learned is that decision support systems that focus just at the level of nation states, or countries, are necessary but not sufficient. We really need to get down to the scale of individual facilities, and even individual pieces of equipment, if we're going to have an impact across civil society," Riley Duren, Carbon Mapper CEO and University of Arizona researcher, told BBC News. "Super-emitters are often intermittent but they are also disproportionately responsible for the total emissions. That suggests low-hanging fruit, because if you can identify and fix them you can get a big bang for your buck."
The new project, announced Thursday, is a partnership between multiple entities, including Carbon Mapper, the state of California, NASA's Jet Propulsion Laboratory (JPL) and Planet, a company that designs, builds and launches satellites, according to a press release. The project is being implemented in three stages.
The initial stage, which is already complete, involved the initial engineering development. NASA and Planet will work together in the second stage to build two satellites for a 2023 launch. The third phase will launch an entire constellation of satellites starting in 2025.
The satellites will include an imaging spectrometer built by NASA's JPL, NASA explained in a press release. This is a device that can break down visible light into hundreds of colors, providing a unique signature for chemicals such as methane and carbon dioxide. Most imaging spectrometers currently in orbit have larger pixel sizes, making it difficult to locate emission sources that are not always visible from the ground. However, Carbon Mapper spectrometers will have pixels of around 98 square feet, facilitating more detailed pin-pointing.
"This technology enables researchers to identify, study and quantify the strong gas emission sources," JPL Scientist Charles Miller said in the press release.
Once the data is collected, Carbon Mapper will make it available to industry and government actors via an open data portal to help repair leaks.
"These home-grown satellites are a game-changer," California Governor Gavin Newsom said of the project. "They provide California with a powerful, state-of-the-art tool to help us slash emissions of the super-pollutant methane — within our own borders and around the world. That's exactly the kind of dynamic, forward-thinking solution we need now to address the existential crisis of climate change."
By Jenna McGuire
Commonly used herbicides across the U.S. contain highly toxic undisclosed "inert" ingredients that are lethal to bumblebees, according to a new study published Friday in the Journal of Applied Ecology.
The study reviewed several herbicide products and found that most contained glyphosate, an ingredient best recognized from Roundup products and the most widely used herbicide in the U.S. and worldwide.
While the devastating impacts of glyphosate on bee populations are more broadly recognized, the toxicity levels of inert ingredients are less understood because they are not subjected to the same mandatory testing by the U.S. Environmental Protection Agency (EPA).
"Pesticides are manufactured and sold as formulations that contain a mixture of compounds, including one or more active ingredients and, potentially, many inert ingredients," explained the Center for Food Safety in a statement. "The inert ingredients are added to pesticides to aid in mixing and to enhance the products' ability to stick to plant leaves, among other purposes."
The study found that these inert substances can be highly toxic and even block bees' breathing capacity, essentially causing them to drown. While researchers found that some of the combinations of inert ingredients had no negative impacts on the bees, one of the herbicide formulations killed 96% of the bees within 24 hours.
According to the abstract of the study:
Bees exhibited 94% mortality with Roundup® Ready‐To‐Use® and 30% mortality with Roundup® ProActive®, over 24 hr. Weedol® did not cause significant mortality, demonstrating that the active ingredient, glyphosate, is not the cause of the mortality. The 96% mortality caused by Roundup® No Glyphosate supports this conclusion.
"This important new study exposes a fatal flaw in how pesticide products are regulated here in the U.S.," said Jess Tyler, a staff scientist at the Center for Biological Diversity. "Now the question is, will the Biden administration fix this problem, or will it allow the EPA to continue its past practice of ignoring the real-world harms of pesticides?"
According to the Center for Food Safety, there are currently 1,102 registered formulations that contain the active ingredient glyphosate, each with a proprietary mixture of inert ingredients. In 2017, the group filed a legal petition calling for the EPA to force companies to provide safety data on pesticide formulations that include inert ingredients.
"The EPA must begin requiring tests of every pesticide formulation for bee toxicity, divulge the identity of 'secret' formulation additives so scientists can study them, and prohibit application of Roundup herbicides to flowering plants when bees might be present and killed," said Bill Freese, science director at the Center for Food Safety. "Our legal petition gave the EPA a blueprint for acting on this issue of whole formulations. Now they need to take that blueprint and turn it into action, before it's too late for pollinators."
ATTN @EPA: Undisclosed "inert" ingredients in #pesticide products warrant further scrutiny! ➡️ A new study compared… https://t.co/bdFwXCVHsD— Center 4 Food Safety (@Center 4 Food Safety)1618592343.0
Roundup — also linked to cancer in humans — was originally produced by agrochemical giant Monsanto, which was acquired by the German pharmaceutical and biotech company Bayer in 2018.
The merger of the two companies was condemned by environmentalists and food safety groups who warned it would cultivate the greatest purveyor of genetically modified seeds and toxic pesticides in the world.
Reposted with permission from Common Dreams.
By Ayesha Tandon
New research shows that lake "stratification periods" – a seasonal separation of water into layers – will last longer in a warmer climate.
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.
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.
By Robert Glennon
Interstate water disputes are as American as apple pie. States often think a neighboring state is using more than its fair share from a river, lake or aquifer that crosses borders.
Currently the U.S. Supreme Court has on its docket a case between Texas, New Mexico and Colorado and another one between Mississippi and Tennessee. The court has already ruled this term on cases pitting Texas against New Mexico and Florida against Georgia.
Climate stresses are raising the stakes. Rising temperatures require farmers to use more water to grow the same amount of crops. Prolonged and severe droughts decrease available supplies. Wildfires are burning hotter and lasting longer. Fires bake the soil, reducing forests' ability to hold water, increasing evaporation from barren land and compromising water supplies.
As a longtime observer of interstate water negotiations, I see a basic problem: In some cases, more water rights exist on paper than as wet water – even before factoring in shortages caused by climate change and other stresses. In my view, states should put at least as much effort into reducing water use as they do into litigation, because there are no guaranteed winners in water lawsuits.
Alabama, pay attention to Supreme Court ruling against Florida in water war #Water #SDG6 https://t.co/wIjdoY6Ccr— Noah J. Sabich (@Noah J. Sabich)1617800452.0
Dry Times in the West
The situation is most urgent in California and the Southwest, which currently face "extreme or exceptional" drought conditions. California's reservoirs are half-empty at the end of the rainy season. The Sierra snowpack sits at 60% of normal. In March 2021, federal and state agencies that oversee California's Central Valley Project and State Water Project – regional water systems that each cover hundreds of miles – issued "remarkably bleak warnings" about cutbacks to farmers' water allocations.
The Colorado River Basin is mired in a drought that began in 2000. Experts disagree as to how long it could last. What's certain is that the "Law of the River" – the body of rules, regulations and laws governing the Colorado River – has allocated more water to the states than the river reliably provides.
The 1922 Colorado River Compact allocated 7.5 million acre-feet (one acre-foot is roughly 325,000 gallons) to California, Nevada and Arizona, and another 7.5 million acre-feet to Utah, Wyoming, Colorado and New Mexico. A treaty with Mexico secured that country 1.5 million acre-feet, for a total of 16.5 million acre-feet. However, estimates based on tree ring analysis have determined that the actual yearly flow of the river over the last 1,200 years is roughly 14.6 million acre-feet.
The inevitable train wreck has not yet happened, for two reasons. First, Lakes Mead and Powell – the two largest reservoirs on the Colorado – can hold a combined 56 million acre-feet, roughly four times the river's annual flow.
But diversions and increased evaporation due to drought are reducing water levels in the reservoirs. As of Dec. 16, 2020, both lakes were less than half full.
Second, the Upper Basin states – Utah, Wyoming, Colorado and New Mexico – have never used their full allotment. Now, however, they want to use more water. Wyoming has several new dams on the drawing board. So does Colorado, which is also planning a new diversion from the headwaters of the Colorado River to Denver and other cities on the Rocky Mountains' east slope.
Utah Stakes a Claim
The most controversial proposal comes from one of the nation's fastest-growing areas: St. George, Utah, home to approximately 90,000 residents and lots of golf courses. St. George has very high water consumption rates and very low water prices. The city is proposing to augment its water supply with a 140-mile pipeline from Lake Powell, which would carry 86,000 acre-feet per year.
Truth be told, that's not a lot of water, and it would not exceed Utah's unused allocation from the Colorado River. But the six other Colorado River Basin states have protested as though St. George were asking for their firstborn child.
In a joint letter dated Sept. 8, 2020, the other states implored the Interior Department to refrain from issuing a final environmental review of the pipeline until all seven states could "reach consensus regarding legal and operational concerns." The letter explicitly threatened a high "probability of multi-year litigation."
Utah blinked. Having earlier insisted on an expedited pipeline review, the state asked federal officials on Sept. 24, 2020 to delay a decision. But Utah has not given up: In March 2021, Gov. Spencer Cox signed a bill creating a Colorado River Authority of Utah, armed with a $9 million legal defense fund, to protect Utah's share of Colorado River water. One observer predicted "huge, huge litigation."
How huge could it be? In 1930, Arizona sued California in an epic battle that did not end until 2006. Arizona prevailed by finally securing a fixed allocation from the water apportioned to California, Nevada and Arizona.
Litigation or Conservation
Before Utah takes the precipitous step of appealing to the Supreme Court under the court's original jurisdiction over disputes between states, it might explore other solutions. Water conservation and reuse make obvious sense in St. George, where per-person water consumption is among the nation's highest.
St. George could emulate its neighbor, Las Vegas, which has paid residents up to $3 per square foot to rip out lawns and replace them with native desert landscaping. In April 2021 Las Vegas went further, asking the Nevada Legislature to outlaw ornamental grass.
The Southern Nevada Water Authority estimates that the Las Vegas metropolitan area has eight square miles of "nonfunctional turf" – grass that no one ever walks on except the person who cuts it. Removing it would reduce the region's water consumption by 15%.
Water rights litigation is fraught with uncertainty. Just ask Florida, which thought it had a strong case that Georgia's water diversions from the Apalachicola-Chattahoochee-Flint River Basin were harming its oyster fishery downstream.
That case extended over 20 years before the U.S. Supreme Court ended the final chapter in April 2021. The court used a procedural rule that places the burden on plaintiffs to provide "clear and convincing evidence." Florida failed to convince the court, and walked away with nothing.
Robert Glennon is a Regents Professor and Morris K. Udall Professor of Law & Public Policy, University of Arizona.
Disclosure statement: Robert Glennon received funding from the National Science Foundation in the 1990s and 2000s.
Reposted with permission from The Conversation.