By Jason West and Yang Ou
About one of every 25 deaths in the U.S. occurs prematurely because of exposure to air pollution. Dirty air kills roughly 110,000 Americans yearly, which is more than all transportation accidents and shootings combined.
When the U.S. Environmental Protection Agency (EPA) weighs decisions about air pollution regulations, it typically selects candidate actions from one or more sectors, such as electric power generation and industry. For each strategy considered, the agency carefully estimates the costs and benefits, then decides which actions to pursue.
We study air pollution and options for reducing it. In a newly published study, we flipped the traditional approach around by starting with the goal of finding emission control actions, among all sources, that could save a specified number of lives for the lowest cost. In doing so, we identified a set of low-cost actions to reduce air pollutant emissions from highly polluting industrial and residential sources, such as residential wood-burning furnaces, that can provide highly cost-effective health benefits.
The U.S. has made tremendous progress in reducing air pollution since 1990, and this has produced significant public health improvements. But air pollution still imposes a serious health burden on the U.S. population, and there are signs that past progress in improving air quality may now be leveling off. New ways of analyzing actions to control air pollution and its health impacts can help.
The number of bad air days in 35 major U.S. cities has plateaued since 2013. U.S. EPA
An Alternative Approach
Under the 1970 Clean Air Act, it is the EPA's job to set National Ambient Air Quality Standards. These regulations limit concentrations of six major air pollutants that harm public health and the environment. Then each state adopts actions that will meet these standards, such as reducing emissions from power plants or large industries.
The EPA also sets limits on emissions from some specific sources over which it has legal authority, including new power plants and motor vehicles. In doing so, the agency aims for air that is considered healthy for all Americans to breathe.
For each strategy considered, the EPA often runs a full cost-benefit analysis. This approach requires a complex atmospheric model to estimate how each proposed action will affect air pollutant concentrations, and the health impacts that will result. This limits the number of options that can be considered.
Our study focused on fine particulate matter, known as PM2.5. We created a framework that simplified the complexity of the atmosphere and air pollution's health impacts. For each U.S. state we calculated impact factors, which represent deaths related to PM2.5 exposure per ton of emissions of different chemical components from different sources. Then we fed these impact factors into an economic model of the U.S. energy system, allowing the model to calculate deaths for any strategy.
Next we set a limit on total deaths caused by PM2.5, and let the model select the least expensive set of actions that would meet energy needs – an important factor because energy use is a major air pollution source – while keeping PM2.5-related deaths below our ceiling. Our model projected future scenarios to 2050, so we considered different ceilings at various points in time, and observed the actions the model selected.
This alternative approach has the advantage of considering a wide range of possible control strategies that affect many different sources. It prioritizes the actions that most cost-effectively reduce premature deaths. Further, by considering these actions in the context of the broader energy system, we can include actions like fuel switching and energy efficiency as alternatives, and quantify consequences of actions throughout the U.S. energy system.
High Particulate Emitters
Using this approach, we pinpointed a set of sources whose emissions contribute disproportionately to PM2.5 mortality impacts. They include factories and other industrial facilities powered by coal and oil, and wood-fired residential furnaces. Emissions from these sources are rising and may continue to increase in the future without additional controls.
Our model showed that reducing emissions from these sources – mainly by electrifying them – could cut projected national air pollution-related deaths in 2050 in half very cost-effectively. Overall national health benefits from these reductions would be roughly seven times the cost of the pollution controls. As many studies have found, air pollution controls tend to be very cost-effective because these emissions cause people to die prematurely through cardiovascular diseases, stroke, lung cancer and other long-term illnesses.
Reductions in the costs of PM2.5-related deaths due to emission reductions from each state, from a scenario that cuts projected national PM2.5-related deaths in 2050 in half. Ou et al., 2020., CC BY
Our study shows that this approach would reduce PM2.5-related emissions in each state. Progress would be greatest in northern and eastern states, including Ohio and Pennsylvania. These regions have many large industrial sources and are densely populated, which means that many people benefit from cleaner air.
Ohio has the largest potential for cost-effectively reducing PM2.5 deaths through cutting industrial coal emissions. California would benefit most from controls on residential wood burning, and Texas would see the greatest reductions in emissions from large petrochemical industries.
We also found that these actions had little influence on overall energy usage in the U.S., and therefore little effect on greenhouse gas emissions. This was interesting because previous research has found that most initiatives to reduce greenhouse gases – which typically involve switching to less-polluting fuels, such as going from coal to natural gas to renewables – also reduce air pollutant emissions, with significant benefits for public health. But the opposite is not true: Low-cost air pollution controls do not appear to have a big influence on U.S. greenhouse gas emissions.
The costs and health benefits of identified low-cost actions to reduce projected national 2050 PM2.5-related deaths by 10% to 50%. Yang Ou, CC BY-ND
Looking Forward to Cleaner Air
Our approach finds the least-cost way of reducing the health impacts of fine particle pollution among all Americans. But it does not ensure that current standards will be met everywhere. One limitation of our method is that we analyzed emissions at the state level, but our current model does not permit us to look more closely at air quality and health impacts for individual urban areas within states that exceed fine particle standards.
Still, our methods offer another tool that the EPA and states can use to help in planning air quality improvements, and the actions identified as being cost-effective for improving health can be compared with those currently being pursued. Spotlighting alternative pollution reduction options can help federal and state regulators make decisions about energy resources and their environmental and health impacts for the coming decades.
As natural gas and renewable energy prices fall, energy industries are in the midst of a transition driven by new technologies and changing economics. As this shift takes place, it is important to consider how to meet new energy demands while reducing greenhouse emissions and the health impacts of air pollutants. We hope our methods will be useful in informing these decisions in the U.S. and elsewhere.
Inefficient wood stoves and wood-burning furnaces are major fine particle sources. Madison & Dane County Public Health
Jason West is a professor of environmental sciences and engineering at the University of North Carolina at Chapel Hill.
Yang Ou is a postdoctoral associate at the Pacific Northwest National Laboratory.
Disclosure statements: Jason West receives funding from the EPA, NASA, NSF, the Donald and Jennifer Holzworth Faculty Acceleration Fund in Climate Change, and the State of North Carolina.
Yang Ou was supported by the Research Participation Program at the Center for Environmental Measurement and Modeling, U.S. Environmental Protection Agency, administered by the Oak Ridge Institute for Science and Education (ORISE).
Reposted with permission from The Conversation.
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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.
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.
Drought conditions in the continental U.S. on April 13, 2021. U.S. Drought Monitor, CC BY-ND
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.