14 Jul 2014:
Human Activity Has Caused
Long-term Australian Drought, Model Shows
A new high-resolution climate model shows that southwestern Australia's long-term decline in fall and winter rainfall, which began around 1970 and has increased over the last four decades, is caused by
increases in man-made greenhouse gas emissions and ozone depletion, according to
research published in Nature Geoscience
. Simulating both natural and man-made climate effects, scientists showed that the decline in rainfall is primarily driven by human activity. Rises in greenhouse gas emissions and thinning of the ozone hole have led to changes in large-scale atmospheric circulation, including a poleward movement of the westerly winds and increasing atmospheric surface pressure over parts of southern Australia. This has led to decreased rainfall, the study said. The drying is most severe over southwest Australia, where the model forecasts a 40 percent decline in average rainfall by the late 21st century, with significant implications for regional water resources.
07 Jul 2014:
A Strong Rebuke for Paper
That Forecasted `Climate Departure’
Thirteen climate scientists and meteorologists have published a sharp criticism
of a paper
by University of Hawaii biogeographer Camilo Mora, who calculated dates when earth’s climate will move into a new state caused by human-driven global warming. Mora and his ideas were featured in an interview
last week at Yale Environment 360
. In a comment article in Nature
, the 13 scientists say that Mora and his colleagues used faulty methodology that produced artificially early dates when specific regions would reach “climate departure.” They also said Mora underestimated the uncertainty involved in forecasting the time of emergence of a new climate regime. “This overconfidence could impair the effectiveness of climate risk management decisions,” the 13 scientists said in their comment. In his own comment
, Mora defended his methods, saying, “Our findings are conservative and remain unaltered in the light of their analysis.”
03 Jul 2014:
Human Activity Has Boosted
Plant Growth Globally, NASA Data Show
On a global scale, the presence of people corresponds to more plant growth, according to
an analysis of three decades of global vegetation greenness data from
Agriculture has increased global vegetative cover.
satellites. More than 20 percent of global vegetation change can be attributed to human activities, such as agriculture, nitrogen fertilization, and irrigation, rather than climate change, researchers report in the journal Remote Sensing
. The findings suggest that global climate change models, which typically don't consider human land use, should take into account the relatively large impact human settlements can have on vegetative cover, the researchers say. From 1981 to 2010, areas with a human footprint saw plant greenness and plant productivity increase by up to 6 percent, while areas with a minimal human footprint, such as rangelands and wildlands, saw almost no change. Most increases in growth and greenness were seen near rural areas and villages, where agriculture is more intense.
Interview: Where Will the Earth
Head After Its ‘Climate Departure’?
The term “climate departure” has an odd ring, but its meaning is relatively straightforward. It marks the point at which the earth’s climate begins to cease resembling
what has come before and moves into a new state where the extreme becomes the norm. Camilo Mora — a University of Hawaii biogeographer, ecologist, and specialist in marshaling big data for climate modeling — has calculated a rough idea for the time of the earth’s climate departure: 2047. That date varies depending on region
, he says. But in a widely publicized paper published in the journal Nature
last year, Mora and 13 colleagues explored the concept of climate departure and what it will mean for our planet. In an interview with Yale Environment 360
, Mora explains why tropical regions will be most profoundly affected by climate change, why controlling population growth is at the core of the challenge posed by global warming, and the frustrations he and other scientists feel as their warnings about rising temperatures are ignored.
01 Jul 2014:
Small Island Nation of Kiribati
Purchases Foreign Land as Climate Refuge
The small island nation of Kiribati has purchased a swath of land in Fiji as a refuge for citizens who may be displaced by rising sea levels, marking the first time a
Kiribati's location (red) in the Pacific Ocean.
country has taken such actions as a defense against climate change, the Guardian reports
. Kiribati, home to 110,000 people scattered across 33 islands in the Pacific Ocean, is one of several small island nations in the Pacific and Indian oceans that could be extensively or completely submerged within a few decades. The cost of protecting such countries often far outweighs their national incomes. Kiribati, with a GDP of under $200 million, ranks among the 10 countries facing the most severe financial impacts of climate change. The tract of 20 square kilometers on the island of Vanua Levu, Fiji, could provide a future refuge for all of Kiribati's citizens, the nation's president said.
30 Jun 2014:
Antarctica's Emperor Penguins
To Be in Serious Decline By 2100, Study Says
Antarctica's Emperor penguins are facing dramatic declines by the end of the century and should be given endangered species status because of the threats posed
Sea ice loss threatens Emperor penguins.
by climate change, according to
an international group of scientists. If sea ice declines at the rates projected by current climate models, at least two-thirds of the colonies will likely shrink by more than 50 percent by 2100, the researchers report in Nature Climate Change
. That conclusion follows a 50-year study in eastern Antarctica of Emperor penguins, an iconic Antarctic species with 45 known colonies. Emperor penguins' survival is highly dependent on sea ice concentrations because they breed on the ice, and too little sea ice reduces the habitat for krill, a critical food source for the penguins. Granting the species protected status under the U.S. Endangered Species Act will provide tools for improving fishing practices of U.S. vessels in the Southern Ocean and potentially for reducing CO2 emissions in the U.S. under the Clear Air Act, the researchers say.
27 Jun 2014:
Going Vegetarian Could Halve
A Consumer’s Food-related CO2 Footprint
A new study of more than 50,000 people in the United Kingdom shows that going vegan, vegetarian, or even “pescatarian” can drastically reduce
people’s carbon footprints. Published in the journal Climatic Change
, the study concluded that if people eating more than 100 grams of meat a day went vegan, their food-related carbon footprint would shrink by 60 percent. If a person eating more than 100 grams of meat per day — and U.S. consumers eat about 225 grams daily — cut down to 50 grams per day, their food-related CO2 emissions would fall by a third, the study said. Pescatarians, who eat fish but no other meat, generate only 2.5 percent more CO2 emissions than vegetarians, according to the study. The research also concluded that vegans produce 25 percent fewer CO2 emissions than vegetarians, who still eat eggs and dairy. “In general there is a clear and strong trend with reduced greenhouse gas emissions in diets that contain less meat,” said Oxford University researcher Peter Scarborough, a co-author of the study.
20 Jun 2014:
Summer Temperatures in U.S.
Have Risen Up To 5 Degrees Since 1970
Summer temperatures in the U.S. have been rising on average 0.4 degrees F per decade since 1970, or about
2 degrees F overall, but the Southwest and West regions have borne the brunt of those increases, according to an analysis by Climate Central
. In the Southwest, temperatures have risen an average of 0.6 degrees per decade, with a few localized areas warming as much as 0.9 degrees per decade. In the West, some parts of California and Nevada have warmed 1.32 degrees F per decade, or more than 5 degrees total since 1970. On the other end of the spectrum, the Upper Midwest has seen the lowest increases. Temperatures in that region have increased only 0.1 degree F per decade on average. The National Climate Assessment
, released last month, found that annual average temperatures in the U.S. could increase by 10 degrees F before the end of the century if the rate of greenhouse gas emissions doesn't slow.
19 Jun 2014:
Rerouting Flights to Avoid
Contrails Would Slow Climate Change
Rerouting the flight paths of commercial aircraft to minimize the condensation trails, or contrails, they leave behind would help slow global warming, even if
the new flight path is longer, according to research published today
. Contrails, thin clouds composed of ice crystals condensed from an aircraft's exhaust, can persist for 17 hours or more and are likely the single largest contributor to climate change
associated with aviation. They form when a plane passes through parts of the atmosphere that are very cold and moist, usually near high pressure systems. The new research shows that avoiding contrail formation has greater climate benefits than avoiding additional carbon dioxide emissions associated with slightly longer flight routes. For example, for a small aircraft that is predicted to form a contrail 20 miles long, an alternative path that adds less than 200 miles will have a smaller climate impact than the contrail. For a larger aircraft, which emits more CO2 per mile than a smaller plane, the alternative route is preferable if it adds less than 60 miles, according to researchers from the University of Reading.
18 Jun 2014:
Global Energy Systems Must
Prepare for Climate Change, Study Says
Power plants and energy systems around the world will experience potentially disastrous effects from climate change and should develop plans for dealing with those effects, according to a report released today
by the World Energy Council and European researchers. Long-term droughts, for example, could threaten water supplies needed to cool large power plants as they produce electricity, the report notes
. Many energy facilities are also lacking protection from floods, rising seas, and severe weather events — a problem highlighted by the 2011 Fukushima nuclear disaster. Strong global political action could have major impacts on the energy sector, the report says, especially if governments make a coordinated effort to invest in renewable and low-carbon energy and upgrades to power distribution grids.
16 Jun 2014:
Skyscraper-Size Ice Structures
Discovered at Base of Greenland Ice Sheet
Melting and refreezing at the base of the Greenland ice sheet has created massive, complex structures the height of skyscrapers and the width of Manhattan, according to
research published in Nature Geoscience
The hidden formations more than a mile below the surface stand in stark contrast to the nearly flat, smooth exterior of the ice sheet and may accelerate its flow toward the sea, researchers say. Scientists had previously interpreted the irregular topography at the base of the ice as hills or mountains, but ice-penetrating radar revealed that the structures were made of ice rather than rock. Scientists from Columbia University explained that as meltwater at the bottom refreezes over hundreds or thousands of years, it radiates heat into the surrounding ice sheet, making it pick up its pace as the ice becomes softer and flows more easily. Greenland's glaciers appear to be moving more rapidly toward the sea as climate warms, but it's unclear how the refreezing process will influence this trend, researchers said.
13 Jun 2014:
U.S. Energy System Depicted
In New Mapping Tool from Federal Agency
The U.S. Energy Information Administration (EIA) recently launched a mapping system
that allows users to
explore the landscape of energy sources and power plant distribution across the nation. Among the most striking visualizations is this map showing the widespread distribution of natural gas power plants, marking the fossil fuel's growing use as an energy source. The U.S. had 1,714 natural gas power plants in 2012, accounting for 30 percent of the country's electricity generation, Vox reports
. Natural gas plants are easier to build and emit fewer pollutants and roughly half as much CO2 as coal-fired plants. The EIA maps depict numerous aspects of the U.S. power system, including the distribution of wind turbines, solar installations, nuclear power plants, coal-fired plants, hydropower stations, and pipelines. More energy maps
are available at Vox, or users can create their own with the EIA's tool.
09 Jun 2014:
Air Conditioning Can Raise
Urban Nighttime Temperature by 2 Degrees
Excess heat from air conditioners raises outdoor temperatures at night by nearly 2 degrees F (1 degree C), worsening the urban heat island effect and increasing cooling demands, according to research
from Arizona State University. Studying the Phoenix metropolitan area, researchers found that air conditioning systems pumped more waste heat into the air during the day, but the effect on near-surface temperatures was negligible. The same was not true for nighttime temperatures, however, when waste heat significantly boosts air temperatures because of nighttime atmospheric conditions. Air conditioning systems can consume more than 50 percent of total electricity
during extreme heat, the researchers note, and summertime extreme-heat days are projected to become more frequent and intense as a result of climate change. Redirecting waste heat from air conditioning systems to household appliances such as water heaters, for example, could help alleviate the problem, the scientists say. They project that such strategies would save at least 1,200 to 1,300 megawatt-hours of energy per day in the Phoenix metropolitan area alone.
Interview: The Small College That
Launched Fossil Fuel Divestment
When Stanford University announced in May that it would divest its endowment of coal mining companies, it was following the lead of a tiny college in rural Maine
that dubs itself “America’s environmental college.” A year and a half earlier, Stephen Mulkey, the president of Unity College
stood on a stage with Bill McKibben, the founder of 350.org and lead cheerleader for the divestment movement, to announce that his college would be the first institution of higher learning to rid its endowment of all fossil fuel holdings. In an interview with Yale Environment 360
, Mulkey, a climate scientist, talks about the ethical imperative behind the decision to divest, and his vision for, as he puts it, a re-engineering of the way the environmental sciences are taught.
06 Jun 2014:
Brazil Leads the World
In Cutting Deforestation, Analysis Finds
Brazil has become the world leader in reducing deforestation and, at the same time, has increased its soy and beef production, researchers report
Amazon rainforest near Manaus, Brazil
. The country has cut its forest loss by 70 percent since 2004, sparing more than 86,000 square kilometers of rainforests and keeping more than 3.2 billion tons of carbon dioxide out of the atmosphere. Brazil's decline in deforestation in 2013 alone represented a 1.5 percent reduction in global emissions that year, the report says; globally, tropical forest loss
accounts for 15 percent of global carbon dioxide emissions. The analysis credits the success to bold government policies, pressure from environmental groups, and market fluctuations in the price of soy and beef, but the authors warn that these wins may be short-lived without more positive incentives for farmers. “These gains are globally significant, but fragile,” one researcher explained. “We’re bumping up against the limits of what can be achieved through punitive measures.”
04 Jun 2014:
New Ozone-Depleting Gases
Discovered in Atmosphere, Researchers Say
Researchers this week identified three new ozone-depleting gases
in the atmosphere, bringing the total number of such gases discovered this year to seven.
Ozone hole as of September 2013
Alone, none of the three gases were found in concentrations high enough to harm the ozone layer, researchers from the University of East Anglia. But the scientists believe more such gases will likely be discovered, and, cumulatively, they could have a significant impact. Two of the newly discovered gases are chlorofluorocarbons (CFCs) and one is a hydrochlorofluorocarbon (HCFC), both of which were once widely used in refrigerants. All three of the newly discovered gases are likely man-made, researchers said. Both CFCs and HCFCs fall under the Montreal Protocol
, an international agreement that bans the use of 13 such compounds. Including the four new gases discovered earlier this year, there are now a total of 20 known ozone-depleting gases.
02 Jun 2014:
New U.S. Coal Plant Rules
Could Lead to a Steep Drop in Emissions
The Obama administration today unveiled a sweeping new plan
that aims to cut carbon dioxide emissions from the nation’s 600 coal-fired power plants by roughly a third. Gina McCarthy, administrator of the U.S. Environmental Protection Agency, said the new rules would give states maximum flexibility
to achieve the goal of reducing power plant emissions 30 percent below 2005 levels by 2030. Hundreds of coal-fired power plants are expected to close under the EPA plan. But rather than immediately shutting down plants, states would be allowed to reduce emissions by making changes across their electricity systems — by installing new wind and solar generation or energy-efficiency technology, continuing to expand the use of natural gas, and by starting or joining state and regional “cap and trade” programs. “There is no one-size-fits-all solution ... so each state’s path can be different,” said McCarthy. The proposed regulations could be held up by legal challenges. Obama administration officials said the rules would lift the U.S. into a clear global leadership position
on combating global warming.
Video Report: Americans on the
Front Lines of Climate Change
A fire chief in Colorado whose department is battling increasingly intense blazes in the American West. A Texas rancher struggling to operate in the face of years of drought. Oyster farmers in Washington state scrambling to adapt to increasingly acidic waters that are damaging their harvests. These Americans are the subjects of videos created by The Story Group
, a non-profit journalism initiative. The videos are meant to put a human face on the science behind the recently released National Climate Assessment
, which stressed that global warming is already having a major impact on the United States.
Watch the videos.
27 May 2014:
To Sway the U.S. Public,
‘Global Warming’ Beats out ‘Climate Change’
If politicians and scientists want to convey the urgency and importance of a warming world, they are far better off using the term "global warming"
than “climate change,” according to a new report. Produced by researchers at the Yale Project on Climate Change Communication and George Mason University, the report
says that Americans are much more familiar with the term “global warming” and that it engenders more negative associations and concern. Based on recent surveys, the report said moderates, women, Hispanics, political independents, and younger Americans associate “global warming” with alarming developments such as melting glaciers and extreme weather. Among many groups, “global warming” also creates a greater sense of threat to one’s family and future generations. “Scientists often prefer the term climate change for technical reasons, but should be aware that the two terms generate different interpretations among the general public and specific subgroups,” the report said. The survey found that among Republicans the two terms are generally synonymous.
20 May 2014:
Widespread Greenland Melting
Due to Forest Fires and Warming, Study Says
Rising temperatures and ash from Northern Hemisphere forest fires combined to cause large-scale surface melting of the Greenland ice sheet in 2012, an
echo of a similar event that occurred in 1889, a new study
finds. The massive Greenland ice sheet — the second largest ice body in the world after the Antarctic ice sheet — experiences annual melting at low elevations near the coastline, but surface melt is rare in the dry snow region in its center. In July 2012, however, satellites observed for the first time surface melt across more than 97 percent of the ice sheet, generating reports that the event was almost exclusively the result of climate change. In the new report, published in the journal Proceedings of the National Academy of Sciences
, researchers found that in both 2012 and 1889 exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires to darken the surface of the ice sheet to a critical albedo threshold, causing the large-scale melting events. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, large-scale melt events on the Greenland ice sheet may begin to occur almost annually by 2100, the researchers say.
15 May 2014:
Intensity of Hurricanes
Now Peaking Farther From the Equator
Powerful, destructive tropical cyclones are now reaching their peak intensity farther from the equator and closer to the poles, according to a new study
in the journal
Hurricane Sandy's progression in 2012
. Over the last 30 years, tropical cyclones, also known as hurricanes or typhoons, have moved poleward at a rate of roughly 33 miles per decade in the Northern Hemisphere and 38 miles per decade in the Southern Hemisphere. Ocean temperatures between 82 and 86 degrees F seem to be "ideal for the genesis of tropical cyclones," said MIT scientist Kerry Emanuel, who co-authored the study, "and as that belt migrates poleward, which surely it must as the whole ocean warms, the tropical cyclone genesis regions might just move with it." The poleward shift of hurricanes and typhoons could lead to "potentially profound consequences to life and property" in regions that previously had not been hit by tropical cyclones.
Five Questions for John Holdren
On the U.S. Climate Assessment
The federal government this month released its National Climate Assessment
, the most comprehensive report to
John P. Holdren
date on the climate impacts already being felt in the U.S. Saying climate change “has moved firmly into the present,” the report documented how drier regions are growing drier, heat waves more intense, and large swaths of forest dying from insect infestations. Yale Environment 360
asked John P. Holdren, director of the White House Office of Science and Technology Policy, five questions about the report and about plans by President Obama to intensify actions to rein in CO2 emissions and adapt to rising seas and other changes. Read more.
14 May 2014:
Early El Niño Conditions
May Spell Big Weather Impact This Year
Indications are growing that an El Niño weather pattern may be forming in the Pacific Ocean, which could have a profound impact on global weather. El Niño events are spawned by unusually warm ocean waters in the Pacific,
and these NASA satellite images
are one indication of warmer waters. The images depict sea-surface height anomalies, with above average sea-surface height shown in various shades of brown. Above average sea-surface heights are an indication of warmer waters, which expand as temperatures rise. These two images compare conditions in 1997 — a year with one of the most powerful El Niño events of the 20th century — with conditions this May. If an El Niño pattern does develop this year, it could lead to wetter conditions in western North America and South America, which could help end a severe drought now plaguing the U.S. West. The 1997/98 El Niño also created warmer and drier conditions in much of Asia. Other evidence, including data from a network of buoys in the Pacific, also shows a deep pool of warm waters sliding east across the Pacific since January.
Interview: Can Marine Life Adapt
To the World’s Acidifying Oceans?
As the world’s oceans grow more acidic from increased absorption of atmospheric carbon dioxide, marine scientists are confronting a key question: How well can
organisms like mollusks, crustaceans, and corals adapt to these more corrosive conditions? One of the leading authorities in this field is University of California, Santa Barbara marine biologist Gretchen Hofmann. Her work in recent years has shown, in fact, that some sea organisms that build shells do seem to have some ability to acclimate to more acidic waters. But in an interview with Yale Environment 360
, Hofmann cautions that this adaptive capacity has its limits. The continuing burning of fossil fuels, she says, could push ocean acidity past a tipping point, rendering some mollusks and other organisms unable to build shells.
Read the interview.
13 May 2014:
Half of U.S. is Experiencing
Some Degree of Drought, Analysis Finds
Half of the United States is in the midst of a drought, a recent analysis
from the U.S. National Drought Monitor found, with nearly 15 percent of the nation in extreme to
exceptional drought. Dry conditions are pushing north rapidly, along with warmer temperatures, and soil moisture and groundwater levels are low far in advance of the agricultural peak demand season, according to the National Drought Mitigation Center. Much of the Southwest and Great Plains regions have been in a persistent drought for several years, and as this map prepared by federal agencies shows, an exceptional drought is currently plaguing parts of those regions. The entire state of California is experiencing some level of drought, much of it extreme to exceptional. Snowpack is at half its typical level in many parts of the West and much of the snow has completely melted before it normally would, researchers say. The map is based on measurements of climate, soil, and water conditions from more than 350 federal, state, and local observers around the country.
08 May 2014:
Natural Variations May Account
For Up to Half of Greenland's Warming
Up to half of the recent climate change in Greenland and surrounding regions — which have warmed at roughly twice the pace of the rest of the planet since 1979 — may be due to natural climate variations that originate in the tropical Pacific and are not connected
Meltwater from Russell Glacier
with the overall warming of the Earth, a new study
says. Still, at least half the warming remains attributable to rising global carbon dioxide emissions, according to research published in the journal Nature
. Climate data and advanced computer models show that changes in the western tropical Pacific Ocean, which has been about 0.3 degrees warmer than normal, have caused shifts in atmospheric pressure over the North Atlantic. Those changes set off a stationary wave in the atmosphere that arcs in a great circle from the tropical Pacific toward Greenland, pulling warmer air over that massive island. "Along this wave train there are warm spots where the air has been pushed down, and cold spots where the air has been pulled up," one author explained. "And Greenland is in one of the warm spots."
07 May 2014:
Stanford Drops Coal Stocks
From Its $18.7 Billion Endowment Portfolio
Stanford has become the first major U.S. university to divest its shares in coal-mining companies from its endowment funds, lending support to a growing nationwide movement calling for universities and
Fossil Free Stanford
pension funds to drop investments in fossil fuel companies. Citing guidelines that allow trustees to weigh whether “corporate policies or practices create substantial social injury” when choosing investments for the university's $18.7 billion endowment, the board decided, after five months of deliberation, to purge stakes in up to 100 companies worldwide that derive profits primarily from coal mining. A Stanford spokeswoman said that coal companies constitute a small fraction
of the university's total endowment investments, “but a small percentage is still a substantial amount of money." Board members said their decision was made partly because coal is the most carbon-intensive of any major fossil fuel and that less carbon-intensive energy sources are available.
05 May 2014:
New European Satellites
To Give More Detailed Views of Earth
The European Space Agency has begun launching
a series of satellites designed to collect detailed environmental data around the globe — from radar-based, high-definition imagery to information about the
atmosphere's chemical composition. The first satellite in the ESA's Copernicus program, the Sentinel 1A, was launched last month and has already returned many striking images based on radar data, such as this view of Brussels, Belgium, in which the dense urban area contrasts with the city's heavily vegetated surroundings. Once Sentinel satellite 1B is launched next year, the two will be able to map the entire globe in six days, giving researchers and conservationists a powerful way to monitor both short- and long-term changes in the environment. Four additional groups of satellites are set to launch this year. Those arrays will focus on high-resolution photo imagery, topography, surface temperatures, and atmospheric chemistry.
Carries on in Key Arctic Ecosystem
At a time of rapidly deteriorating relations between Russia and America, U.S. scientist Joel Berger continues his work with his Russian counterparts
Third in a series of blog posts from the Russian Arctic
on Siberia's Wrangel Island. In the third of three blog posts for Yale Environment 360
, Berger — a biologist with the Wildlife Conservation Society and the University of Montana — writes about efforts to better understand how rapid climate change might affect muskoxen and other wildlife in the Russian and North American Arctic. As Berger explains, a key focus of Russian-American scientific cooperation is Beringia, the region of northwestern Alaska and extreme northeastern Russia where two countries — and continents — are divided by the Bering Sea.
28 Apr 2014:
Economic Viability of Nuclear
Power Under Threat, Energy Group Says
Nuclear reactors in the U.S. need a boost — either through carbon taxes or regulations forcing coal-fired plants to slash emissions — or economic factors will force many to close, according to a report
from a non-profit group. Nuclear power — currently the only major zero-carbon, around-the-clock baseload power source — supplies 19 percent of U.S. electricity and is key to meeting President Obama's pledge to reduce emissions 17 percent below 2005 levels by 2020, according to the Center for Climate and Energy Solutions. The economic viability of the 100 nuclear reactors in the U.S. is worsening, the report says, because of the abundance of cheap natural gas and rising wind energy production. A carbon tax or some form of carbon trading — for instance, requiring coal-fired plants to purchase and blend their electricity output with nuclear power — will be essential to keeping nuclear plants from closing before the end of their lifespans, the report contends. Four power companies recently announced the early retirement of five nuclear reactors, which constitute more than 4 percent of U.S. nuclear capacity, the group says.