CS3 In the News

China Energy and Climate Project Director Professor Valerie J. Karplus appeared on Channel NewsAsia to discuss the impacts and broader significance of the Korean emissions trading system kicking off last week. Watch the interview below.


 

Anna Petherick writes for Nature Climate Change about emissions pledges from the United States and China for, including emissions projections from China Energy and Climate Project.

Read the full column here.

Amanda Peterka | E&E reporter

Bioenergy production would boom and spur steep reductions in greenhouse gas emissions if a global price is slapped on carbon, Massachusetts Institute of Technology researchers say in a report released today.

Examining bioenergy production under a $15-per-metric-ton carbon price that would rise steadily to $59 in 2050, researchers found production hitting 150 exajoules by 2050 -- compared with below 50 exajoules without a carbon price.

Global greenhouse gas emissions would plunge 16 percent under that scenario, the report says, cautioning that the carbon price studied doesn't take into account land-use changes. Taking into account emissions from land-use changes, including deforestation, it says greenhouse gas reduction would be nearly 60 percent from the no-carbon-price baseline.

"The study is one of the most in-depth evaluations to date of how bioenergy might fit into a low-carbon future," MIT said in a release. "The research team developed a cutting-edge modeling tool covering a comprehensive range of bioenergy pathways."

The MIT Joint Program on the Science and Policy of Global Change says its study goal was to see how bioenergy would compete with other low-greenhouse-gas options on a level playing field.

The researchers used the Economic Projection and Policy Analysis model to create both the carbon price scenarios and assumptions about economic, productivity and population growth without a carbon price. The model examined seven first-generation biofuel crops and two cellulosic biofuel conversion technologies -- bioelectricity and heat.

The model also accounted for international trade, ethanol blending limits, changes in land and production costs, and existing policies such as the federal renewable fuel standard, among other factors.

"Biofuels are only one channel for bioenergy," said Niven Winchester, an environmental energy economist at MIT. "If you want to study how land can be used to meet our energy needs, you have to think of all the different ways to use what grows on that land -- including food, feed and fuel."

The carbon price scenario resulted in efficiency improvements and energy use reductions, the report says. Electricity consumption in 2050 dropped 19 percent, while there was 73 percent less electricity from coal.

With a carbon price in the MIT model, bioenergy use rose from 8.5 exajoules in 2015 to 152.4 exajoules in 2050 -- or about a quarter of global energy needs.

The model found that corn ethanol would be produced in the United States until 2025, when it would become uneconomical.

After 2025, cellulosic ethanol would become the primary form of bioenergy; by 2020, cellulosic ethanol would account for about 57 percent of the globe's total bioenergy consumption.

Increased energy prices under a carbon price would make grasses -- one of the main inputs for cellulosic ethanol -- more attractive, while cellulosic producers would face lower land costs than other biofuel producers, according to the report. Rising electricity prices would also increase the revenue that cellulosic producers could receive from producing electricity as a co-product.

Africa and Brazil would become the largest bioenergy producers in a world where cellulosic ethanol is the main form of bioenergy, the MIT study found.

"Africa can become a key player in supplying global energy, if agricultural expertise can be transferred to this region," Winchester said. "It has the right climate and a large amount of land, but also the potential for deforestation if policy safeguards aren't in place."

The growth in cellulosic ethanol assumes that production costs fall over the next 35 years and that ethanol-blending constraints disappear by 2030 partly through the use of more flex-fuel cars.

MIT found that pricing greenhouse gas emissions from bioenergy land-use changes significantly increases the amount of greenhouse emission reductions that occur as a result of bioenergy expansion.

Pricing land use changes would prompt a global reforestation of 800 million hectares between 2010 and 2050, according to the study. In 2050, cumulative carbon-dioxide-equivalent emissions would be 37,381 million metric tons if land-use changes were priced, compared to 74,140 million metric tons if they were not.

"The report concludes that changes spurred by the carbon price, including bioenergy production, could cut greenhouse gas emissions by more than half, with a catch -- to achieve the cut, the carbon price must cover emissions from changing land use," MIT said. "Without this safeguard, deforestation becomes a major concern as forests are cleared to make way for farmland."

by Jesse Jenkins | The Energy Collective

Jesse Jenkins: Even before world leaders descended on Lima, Peru this week for United Nations-sponsored climate negotiations, climate diplomacy made global headlines with the joint announcement of a partnership between the world's two largest carbon emitters: the United States and China.

The joint pledge to cut greenhouse gas emissions and collaborate on clean energy technology development has been hailed as a potential sea change in the tone and substance of international climate mitigation efforts.

To dig in to the details of this U.S.-China climate partnership, I caught up this week with Valerie Karplus, an assistant professor at the Massachusetts Institute of Technology's Sloan School of Management and Director of the Tsinghua-MIT China Energy Program.

An expert on both American and Chinese energy and climate policy, Prof. Karplus and I explored what the climate deal means for domestic energy policy in each nation, chatted about the major drivers of emissions growth in China, and considered implications of the new emissions pledges for international climate negotiations.

Read the full interview at the Energy Collective

by David L. Chandler | MIT News Office

New research shows that relatively small volcanic eruptions can increase aerosol particles in the atmosphere, temporarily mitigating the global warming caused by greenhouse gases. The impact of such smaller eruptions has been underestimated in climate models, the researchers say, and helps to account for a discrepancy between those models and the actual temperatures observed over the last 15 years.

The findings are reported in a paper in the journal Geophysical Review Letters, co-authored by MIT Professor Susan Solomon, postdoc David Ridley, and 15 others. They help to explain the apparent slowdown in the pace of global warming recorded over the last 10 to 15 years — possibly explaining as much as half of that slowdown, the researchers say.

“We’ve learned a lot of new things about how the Earth’s climate changes, not just from year to year but from decade to decade, as a result of recent research,” says Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “Several independent sets of observations show that relatively modest volcanic eruptions are important.”

For the last several years, “It’s been quite clear that the observed trends are not following what the models say,” Ridley adds: While the overall warming trend continues, its rate is slower than projected. Previous research has suggested that some of that discrepancy can be accounted for by an increase in the amount of warm water being carried down to the deep ocean, but other processes can also contribute.

The cooling effect of large volcanic eruptions, such as that of Mount Pinatubo in the Philippines in 1991, was already widely recognized; the new work shows that smaller eruptions can have a significant cooling effect as well, and provides a better estimate of how much of the recent reduction in warming could be explained by such eruptions: about 30 to 50 percent of the discrepancy, the team found.

The team found that small eruptions produce a significant amount of aerosol particles, which reflect sunlight, in a region of the upper atmosphere that is relatively poorly monitored: Satellites can provide good data about the atmosphere down to around 15 kilometers above ground level, below which clouds interfere. The team filled in the missing region using multiple balloon, laser radar (lidar), and ground-based measurements.

Aerosols in that intermediate zone, from about a dozen modest eruptions around the world during the last 15 years, may double previous estimates of the cooling effect of eruptions, Ridley says.

“It’s always exciting in science when you can find multiple measurements that lead to a common conclusion,” Solomon adds. “Several independent sets of observations now show that relatively modest volcanic eruptions are more important for global climate than previously thought.”

Overall, these smaller eruptions have lowered the increase of global temperature since 2000 by 0.05 to 0.12 degrees Celsius, counteracting some of the warming that would otherwise have occurred. Now, using this new information, groups that carry out climate modeling can update their models to more accurately project global climate change over the coming decades, Ridley says.

Alan Robock, a professor of environmental sciences at Rutgers University, says, “This work helps to better quantify the impacts of the most important natural cause of climate change, volcanic eruptions. We have an imperfect observational system for volcanic aerosols, and this work exploits some previously unused sources of information to better quantify the effects of small eruptions for the past decade.”

Robock, who was not involved in this research, adds that in light of these findings, “We need a more robust observing system for volcanic aerosols, to do a better job of measuring future small eruptions.”

Ridley and Solomon were the lead authors of this paper, joining authors from Wyoming, Russia, Germany, Japan, California, New York, Virginia, Colorado, and the U.K. The work was supported by the National Science Foundation, the Ministry of Science and Education of the Russian Federation, and the Russian Science Foundation.

By Mike Orcutt | MIT Technology Review

China may put a stop to growing carbon dioxide emissions earlier than expected, but how quickly they start coming down is also important.

In an agreement announced last week, China and the United States, which together account for some 45 percent of the globe’s total carbon dioxide emissions, pledged to make significant efforts in the next 10 to 15 years to limit their CO₂ emissions.

It’s the first time China has publicly committed to halting the decades-long rise of its CO₂ emissions. However, due to economic factors and policy shifts, China may be poised to achieve this goal even earlier than promised.

The U.S. pledged that by 2025 the amount of CO₂ it emits annually would drop to 26 to 28 percent below its emission levels from 2005. China meanwhile promised that its annual CO₂ emissions, which have increased by 257 percent since 1990, would stop rising by 2030 or earlier. China also pledged that 20 percent of its energy would come from sources other than fossil-fuels by 2030. That’s up from around 8 percent in 2010.

As recently as 2010, when China’s economy was still growing at more than 10 percent a year, it was unclear when its emissions might peak, says Valerie Karplus, a professor of global economics at MIT’s Sloan School of Management, and director of the Tsinghua-MIT China Energy and Climate Project.

But economic growth has slowed (it was 7.7 percent in 2012), and in turn so has growth in demand for energy.

Also, this year China’s government has already announced a plan to reduce air pollution by taxing and limiting coal use. Beyond that, carbon trading systems are now being tested in five cities and two provinces, and a national system is expected to come online in 2016.

In a recent modeling study that accounted for these new policies and assumed that China would accomplish ambitious near-term goals for expanding nuclear power and renewables, Karplus and collaborators at Tsinghua University in Beijing found that demand for coal could peak sometime between 2020 and 2025, and carbon emissions could level off sometime between 2025 and 2030.

But, says Karplus, there is still uncertainty over when China will begin actually reduce its emissions, and by how much. “It makes a big difference whether it peaks at 10 billion, 11 billion, or 15 billion metric tons of CO₂,” and whether or not the trajectory decreases rapidly after that peak, says Karplus.

Read the full article at MIT Technology Review

By Peter Dizikes, MIT News Office

With cap-and-trade legislation on greenhouse-gas emissions having stalled in Congress in 2010, the Obama administration has taken a different approach to climate policy: It has used the mandate of the Environmental Protection Agency (EPA) to propose a policy limiting power-plant emissions, since electricity consumption produces about 40 percent of U.S. greenhouse gases. (The administration also announced a bilateral agreement with China this week, which sets overall emissions-reductions targets.)

The EPA’s initial proposal is now under public review, before the agency issues a final rule in 2015. Christopher Knittel, the William Barton Rogers Professor of Energy Economics at the MIT Sloan School of Management, is one of 13 economists who co-authored an article about the policy in the journal Science this week. While the plan offers potential benefits, the economists assert, some of its details might limit the policy’s effectiveness. MIT News talked with Knittel about the issue.

Q. How is the EPA’s policy for power plants intended to work?

A. The Clean Power Plan calls for different emissions reductions depending on the state. This state-specific formula has four “buckets:” efficiency increases at the power plant; shifting from coal to natural gas; increases in generation from low-carbon renewables such as wind; and increases in energy efficiency within the state. So they applied these four things and asked what changes were “adequately demonstrated” to generate state-specific required reductions.

Q. The Science piece emphasizes that the EPA’s plan uses a ratio-based means of limiting emissions: the amount of greenhouse gases divided by the amount of electricity consumed. So a state could add renewable energy, lower its ratio, but not reduce total emissions. What are the advantages and disadvantages of doing this?

A. The targets are an emissions rate: tons of CO₂ [emitted] per megawatt-hour of electricity generation. Then it’s really up to the states to determine how they’re going to achieve the reductions in this rate. So one strategy is to increase total electricity generated. This compliance strategy, unfortunately, is what makes rate-based regulation economically inefficient.

The states also have the option to convert that rate-based ratio target into what the EPA is calling a mass-based target, total tons of greenhouse-gas emissions. This would effectively imply the state is going to adopt a cap-and-trade program to reach its requirements.

In current work, we — scholars Jim Bushnell, Stephen Holland, Jonathan Hughes, and I — are investigating the incentives states have to adopt to convert their rate-based mandate into a mass-based mandate. Unfortunately, we are finding that states rarely want to [use a mass-based target], which is a pity, because the mass-based regulation is the most efficient regulation, from an economist’s perspective. Holland, Hughes, and I have done work in the transportation sector that shows that when you do things on a rate base, as opposed to a mass base, it is at least three times more expensive, and more costly to society — often more than five times more costly.

Q. Why did the EPA approach it this way?

A. I can only speculate as to why the EPA chose to define the regulation as a rate instead of total greenhouse gas emissions. Regulating a rate is often cheaper from the firm’s perspective, even though it is economically inefficient. Why the EPA chose to define things at the state level is more clear: The Clean Air Act … is written in such a way to leave it up to the states.

But if everyone’s doing their own rate- or mass-based standard, then you don’t take advantage of potentially a large efficiency benefit from trading compliance across states. That is, it might be cheaper for one state to increase its reductions, allowing another state to abate less.

The most ideal regulatory model is that everyone’s under one giant mass-based standard, one big cap-and-trade market. Even if every state’s doing its own cap-and-trade market, that’s unlikely to lead to the efficient outcome. It might be cheaper for California or Montana or Oregon to reduce their greenhouse-gas emissions, but as soon as they meet their standard, they’re going to stop.

Q. The Science article says that certifying efficiency-based gains is a crucial factor. Could you explain this?

A. Given how the regulation treats efficiency, it really puts in the forefront the importance of understanding the real-world reduction in energy consumption coming from efficiency investments. Let’s say I reduce electricity consumption by 100 megawatt-hours through increasing efficiency in buildings. Within the [EPA’s] policy, that reduction is treated as if I’m generating 100 megawatt-hours from a zero-carbon technology. So that increases the denominator in the ratio [of greenhouse gases produced to electricity consumed]. One concern, though, is that often the actual returns from energy-efficiency investments aren’t as large as the predicted returns. And that can be because of rebound [the phenomenon by which better energy efficiency allows people to consume more of it], which is a hot topic now, or other behavioral changes.

Behavioral changes can make those efficiency gains larger or smaller, so getting the right number is very important. I’ve heard stories of people who get all-new windows, and the old windows used to let in air, but now they think the house is stuffy, so they keep their windows cracked. We should be doing more field experiments, more randomized controlled trials, to measure the actual returns to energy efficiency.

Another related concern is that it might be left up to the states to tell the EPA what the reduction was from these energy-efficiency investments. And the state might not have any incentive at all to measure them correctly. So there has to be an increase in oversight, and it likely has to be federal oversight.

Q. While you clearly have concerns about the efficacy of the policy, isn’t this one measure among others, intended to lessen the magnitude of the climate crisis?

A. For many of us, the potential real benefit from the clean power rule is that it will change the dynamic in Paris in the [forthcoming international climate] negotiations. For a long time the U.S. could say it was doing some improvements in transportation, but they really weren’t doing anything in electricity, for climate change. My view is there are a lot of countries out there that aren’t going to do anything unless the U.S. does. This might bring some of those countries on board.

In this column for the Washington Post Wonk Blog, Michael Levi, senior fellow for energy and the environment at the Council on Foriegn Relations, describes the significance of U.S.-China climate agreement, and research that may have influenced the agreement. 

Read the article here. 

by Zach Wener-Fligner, MIT News correspondent

All around the planet, high-frequency climate observatories are collecting atmospheric data around the clock as part of the Advanced Global Atmospheric Gases Experiment (AGAGE), a 35-year-old project to study emissions and climate change.

But there’s one problem: Despite a network of observatories that covers much of the globe, AGAGE lacks data on Africa — the world’s second-largest continent.

That’s something that Jimmy Gasore, along with other scientists, is trying to change. Gasore, a fourth-year graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences under Ronald G. Prinn, the TEPCO Professor of Atmospheric Science, is working with research scientist Katherine Potter to build the first high-frequency climate observatory in all of Africa.

Once finished, the observatory will sit atop Mount Karisimbi, on the border between Rwanda and the Democratic Republic of Congo, at an elevation of nearly 15,000 feet. (Climate observatories are often built at high elevations so that researchers can cast a wider net, collecting data from a much larger surrounding region.) For now, it’s located at about half that elevation, on Mount Mugogo in Rwanda — making for more efficient work, since the hike up Karisimbi takes two days.

It’s a project that will fill a large hole in our current understanding of emissions of greenhouse gases — especially those coming from agricultural activities, wildfires, and deforestation. This will lead not only to better climate predictions, but also support regional and global climate-change mitigation strategies.

It’s also a highly personal project for Gasore, a citizen of Rwanda.

“We don’t know about African emissions, and we don’t have enough studies in Africa,” Gasore says. “It’s worth doing this study that has the potential to actually change people’s lives. It’s very gratifying to do research that actually affects people.”

Doing what felt right

Growing up in a village in southwestern Rwanda, Gasore used to watch the shadow cast by his house to predict when his mother would come home each day from her job as a schoolteacher — the first time he ever felt like he was really using science.

Gasore was also innately fascinated with how things worked: He was transfixed when he saw mechanics poking around car engines, and would stare as they struggled with the machinery.

“Even today I can watch road work, and tractors, for hours,” he says.

His father was trained as a nurse, but ran an electronics repair shop, fixing radios and televisions. Just from hanging around his father’s shop, a young Gasore learned about electronics by tinkering.

School wasn’t mandatory in Rwanda when Gasore was growing up, but his parents put a heavy emphasis on education for him and his five siblings. He learned to read French when he was 5, but didn’t attend school until he was 7. His father soon started to bring him books on computers and physics.

It just so happened that he had a knack for school — and for math, in particular. At the end of his primary schooling, Gasore was the best student in his district, and then placed third in a nationwide examination. He was awarded a scholarship to the National University of Rwanda, where he studied theoretical physics, graduating first in his class in 2007.

After finishing college, Gasore reached a crossroads. He stayed at the university and worked as a teaching assistant, but could feel himself growing disenchanted with the ethereal world of theoretical physics.

“When I finished I found that I wasn’t well connected with the real world,” he says. “I knew things, but couldn’t actually talk to people and tell them what I knew.”

Gasore was interested in climate science because it offered a mix of the theoretical and the practical. “I love using my theoretical knowledge on real-life problems,” he says.

Before long, an opportunity came knocking. Gasore was familiar with MIT, and the National University of Rwanda had partnerships with the Institute through OpenCourseWare and iLab. When Potter — now his colleague — came to visit Rwanda as part of her research, Gasore asked to meet her.

Potter was impressed with Gasore’s interests and intelligence, and advised him to apply to MIT. He did, and was accepted. The following fall, he moved to Boston.

Carving a path at MIT

Initially, Gasore was surprised by the freedom he found at MIT: “My previous school was sitting in a class and having someone teach you what to do. So I liked getting to choose what I got to study — to have 20 options for classes and to get to choose four.”

He quickly immersed himself in student opportunities surrounding his studies, joining the Weather Forecasting Team, the Joint Program on the Science and Policy of Global Change, and the Center for Global Change Science. Recently, he was also awarded a Martin Family Fellowship for Sustainability, which supports MIT graduate students in environmental studies.

Gasore realizes the importance of being able to talk to policymakers.

“Policy meetings are about climate-change mitigation and emissions abatement. So you have to talk in those terms,” he says. “I think the Center for Global Change Science is very strong in emphasizing strong mathematical skills, but also keeping in mind that we are doing this for policy.”

Above all, Gasore is passionate about his work: “I enjoy doing it. That’s the motivation. That’s why I can spend the night here in the lab troubleshooting,” he says. “There’s a reward when you spend five hours on something and then at the end you see it working and you say, ‘Wow.’ That’s what keeps me going.”

Audrey Resutek and Erwan Monier
MIT Joint Program on the Science and Policy of Global Change
World Meteorological Organization Bulletin, October 17, 2014

The US National Climate Assessment, released this spring by the White House, describes a troubling array of climate woes, from intense droughts and heat waves to more extreme precipitation and floods, all caused by climate change. The report also describes how climate change is expected to impact regions across the United States in the future, yet it notes that exact regional forecasts are difficult to pin down. At the larger scale, it is clear that climate is changing, but local predictions can disagree on the extent to which temperatures will increase, and what regions will be hit the hardest by precipitation changes.

Researchers at the MIT Joint Program on the Science and Policy of Global Change examined four major factors that contribute to wide-ranging estimates of future regional climate change in the United States, with an eye toward understanding which factors introduced the most uncertainty into simulations of future climate. They find that the biggest source of uncertainty in climate modelling is also the only one that humans have control over – policies that limit greenhouse gas emissions.

In this context, the term “uncertainty” does not mean that there is a lack of scientific consensus that climate is changing. Instead, uncertainty refers to the fact that using different assumptions for the variables that go into a climate model – for example, the amount of greenhouse gases emitted over the next century, or how sensitive the climate is to changes in carbon dioxide levels – will produce a range of estimates. Overall, these estimates indicate that the Earth will be a warmer and wetter place over the coming century, but there is no single niversally agreed on amount of climate change that will take place.

In fact, estimates that point to a single number for changes in temperatures and precipitation may be misleading, precisely because they do not capture this uncertainty. It is more useful to think of estimates of future climate change as a range of possible effects. The range of potential warming, for example, follows a bell curve, with the most likely change in temperature falling at the highest point of the curve. The farther you travel from the curve’s peak, toward the tails, the more unlikely the temperature change. While the extreme temperature increases at the curve’s tails are unlikely, they still fall within the realm of possibility, and are worth considering because they represent-worst case scenarios.

Read the full article in the World Meterological Organization Bulletin

Helen Hill (EAPS)
MIT News
October 10, 2014

Peter Hale Molnar, professor of geological sciences at the University of Colorado at Boulder and a fellow at the Cooperative Institute for Research in Environmental Sciences in Boulder, Colo., presents the 2014 John Carlson Lecture at 7 p.m. on Thursday, Oct. 16 at the New England Aquarium.

The title of his talk is: “Big Cats, Panamá, and Armadillos: A Story of Climate and Life."

Three million years ago, ice covered what is now Canada for the first time in the first “ice age” in hundreds of millions of years. In that ice age, the sheet of ice covering North America reached as far south as modern-day Missouri. Approximately 100 subsequent ice ages have occurred since that time, with the retreat from the last one occurring between 20,000 and 10,000 years ago.

Concurrently, ancestors to mountain lions crossed the Isthmus of Panamá, from North America to South America, to wreak havoc among animal life there, while giant armadillo-like animals moved in the opposite direction into North America. Mountain lions and armadillos are but two among many species that made such journeys, in what biologists call the “Great American Interchange.”

Many geologists who study past climates — paleoclimatologists — imagine that the Isthmus of Panamá emerged 3 million years ago, not only to provide a land bridge for the interchange of animals, but also to isolate the Atlantic and Pacific Oceans, and, as a consequence, to alter ocean circulation. That circulation today includes features like the Gulf Stream, an ocean current that transports warm water from the eastern coast of the U.S. to western Europe. These paleoclimatologists infer that the marked change in ocean circulation created conditions that allowed ice sheets to grow on the North American continent and to give us recurring ice ages.

Suppose, however, that you were a mountain lion, or an armadillo; would anything draw you into the swamps and jungles of hot, humid Panamá? Would you not prefer to remain in your semi-arid savanna than deal with snakes and crocodiles?

During ice ages, Panamá cools a bit and dries out, making it like the more arid climates where mountain lions, armadillo, and their brethren flourish. So, alternatively, could global climate change associated with that first big glacial period have temporarily transformed Panamá’s mosquito-infested, uninviting jungles into a savanna highway conducive to overland travel? In terms of cause-and-effect, rather than the Great American Interchange signaling a change in the configuration of land and sea whose resulting ocean circulation facilitated the first ice age, could the interchange, instead, be a consequence of the global climate changes due to that first glacial period, whose cause would lie elsewhere, independent of the emergence of the Isthmus of Panamá?

In his talk, Molnar will grapple with this and related questions as he explores different theories about our planet’s climate history spanning human and geological time scales.

The John Carlson Lecture communicates exciting new results in climate science to the general public. Free of charge and open to the general public, the lecture is made possible by a generous gift from John H. Carlson '83 to the Lorenz Center in the MIT Department of Earth, Atmospheric and Planetary Sciences.

For additional information, please contact either Jen Fentress or Allison Provaire or call 617-253-9397.

Bobby Magill
Climate Central

Water stress — the general scarcity of freshwater for people who need it — is considered by many scientists as one of the biggest challenges facing humanity and struggling ecosystems in a world increasingly affected by climate change.

Studies differ on how much the world’s growing population will be affected by the growing difficulty of finding freshwater, but a new report by researchers at the Massachusetts Institute of Technology have found that climate change could actually provide more water to people in some parts of the globe while reducing freshwater for other areas.
 
Global warming may increase the overall amount of freshwater flowing in rivers worldwide by about 15 percent, easing water scarcity in many places, including the U.S. Midwest, according to MIT’s Energy and Climate Outlook 2014, released Monday.

By the end of the century, during which time greenhouse gas emissions could double globally, the MIT outlook projects that water scarcity could also ease in Mexico, Saudi Arabia, Libya, China and Western Europe. In other places, water stress could worsen, especially in the U.S. Southwest, Pakistan, Turkey, South Africa and parts of North Africa.

“All climate models predict a speedup of the hydrological cycle with warmer temperatures,” said the study’s lead author, John Reilly, co-director of the Joint Program on the Science and Policy of Global Change at MIT’s Center for Environmental Policy Research. “That means faster evaporation, more moisture in the atmosphere and more rainfall.”

MIT researchers project that while more moisture in the atmosphere will increase freshwater flow 15 percent globally by the end of the century, consumption of freshwater for all human uses worldwide is expected to increase 19 percent, including water for industrial, domestic and agricultural uses.

Of those uses, the outlook shows that domestic freshwater consumption could double from 348 billion cubic meters in 2010 to 698 billion cubic meters in 2100, and industrial use of water could increase from 763 billion cubic meters to 1,098 billion cubic meters, or about 45 percent. Irrigation use is projected to decline slightly worldwide.

But more freshwater doesn’t paint the full picture. In a warming world, how and if that water can be made available for people to use gets complicated.

Exploding human populations may overwhelm water supplies, creating new areas of water stress, according to the outlook.

“This water stress arises because of increased water demand, and in some cases reduced runoff,” Reilly said. “As with almost all climate models, we project more precipitation poleward, and generally drier conditions in subtropical regions.”

And, freshwater availability depends on how and when it falls from the sky.

“Water stress, or not, is very much a function of precipitation in the right place at the right time, and in the right form,” Reilly said.

Rain may begin to fall at times when it can’t be used for irrigation or can’t be captured for storage in reservoirs, he said.

A big concern is precipitation falling as rain rather than snow, or snowpack melting earlier in areas that depend on snowmelt, such as much of the western U.S., he said.

“Snowpack is nature’s water storage, slowly releasing water far into summer dry months and therefore providing even timing even when summers are dry,” Reilly said. “With less snowpack storage, we would need to make up for it by building reservoirs where possible.”

A drought-ravaged village in Mauritania. Credit: United Nations/flickr Building new reservoirs is a costly proposition, and they’d have to be built to handle the added challenge of capturing water from extreme rainfall.

“There is a general conclusion that more rain is likely to come in heavier downpours, with longer periods in between,” he said. “So that raises the specter of both flooding and drought because in a heavy downpour most of the water runs off, and unless there is man-made storage somewhere, it quickly ends up in the sea, and is no longer fresh water.”

That’s a major concern in Rocky Mountain states such as Colorado, which contains the headwaters of some of the most important rivers in the West, including the Colorado River, which provides water to drought-stricken Phoenix and Los Angeles.

Spring snowmelt in Colorado could come up to 17 days earlier than today, and some rivers the state relies on for fresh water supplies could see streamflows decline by up to 35 percent, according to a 2012 Colorado climate vulnerability study.

“As the climate warms, more water will evaporate and sublimate from mountain snowpacks before it ever reaches reservoirs, and agricultural demand will rise,” meaning that there will be less water to go around as a booming population conflicts with a decreasing and less predictable water supply, Colorado State University atmospheric scientist Scott Denning told Climate Central in January.

The MIT report cautions that any projections of regional precipitation patterns and the processes that control runoff from mountain snowpack in a warming world are extremely uncertain, and rain and snowfall are likely to vary widely from year to year and decade to decade.

Not all studies focusing on water security have shown water stress easing much at all in a warming world.

A 2013 study by researchers at the Potsdam Institute for Climate Impact and Research showed that declining precipitation and increasing evapotranspiration will strain water supplies in many areas, especially the U.S. Southwest, affecting 2 billion people globally.

A Pacific Northwest National Laboratory (PNNL) study published in August showed that without any climate policy curbing global greenhouse gas emissions, half of the world’s population is will be living under “extreme” water scarcity by the end of the century.

These studies reach different conclusions because there are multiple ways to measure water stress: Some studies focus only on water supply, while others, such as the MIT report, focus on both supply and demand. Each study also uses its own assessment of hydrology, the effects of climate change and other factors, said PNNL climate scientist Mohamad Hejazi, lead author of the PNNL water scarcity study.

In some cases, studies may significantly underestimate overall water deficit in some areas in a warming world, he said.

“This (MIT) study constitutes one plausible scenario, but it is not definitive,” he said.

MIT’s report was published Monday following the United Nations Climate Summit in New York the previous week, when the Obama administration committed to greenhouse gas emissions cuts to be included in a treaty expected to be signed in Paris in 2015. The Paris negotiations will be known as COP 21, or the 21st Conference of the Parties to the UN Framework Convention on Climate Change.