Cooperative Institute for Research in Environmental Sciences

The area covered by crevasses northeast of Ilulissat, West Greenland, has expanded by 13 percent over the last 24 years, according to scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES)—a change that may impact the sliding of the Greenland Ice Sheet and subsequent sea level rise.

“The area covered by crevasses is increasing,” said CIRES research associate William Colgan, lead author of the study published online today in Geophysical Research Letters. “Theoretically, this change may cause the ice sheet to slide more slowly toward the coast or into the ocean.”

Colgan and his coworkers, a team led by CIRES Director Konrad Steffen at the University of Colorado Boulder, investigate the slide of the Greenland Ice Sheet, the second largest ice sheet on Earth. “People typically think of a block of ice as something really solid and inflexible,” Colgan said. “But when a block of ice is as big as the Greenland Ice Sheet, there is sufficient pressure from its weight to cause it to flow like a really, really slow river into the ocean.”

The weight of the ice causes the sheet to flow like a viscous fluid, and water between the ice sheet and its bed means the sheet slides as well as flows, Colgan said. The flow and sliding of the ice sheet can cause more ice than normal to flow into the ocean, which can lead to sea level rise, he said. “It is really important to understand how the Greenland Ice Sheet flows, slides and melts today, in order to be able to predict how it will contribute to sea level rise in the future.”

To investigate the impact of crevasses on ice sheet flow, the team first analyzed crevasse extent at Sermeq Avannarleq, northeast of Ilulissat, West Greenland. The scientists detected crevasses in high-resolution digital images taken in 1985 and 2009 and what they found surprised them. “We initially weren't looking for changes in crevasse area, we had thought it was stationary in time,” Colgan said. “But we found that the change in crevasse area was significant.”

Several factors influence the extent of crevasses, Colgan said. The weight of ice surrounding the crevasse acts as a “closing” force on crevasses whereas tensile stress, caused by local variations in surface slope, acts as an “opening” force. Warmer temperatures, however, result in increased surface melt and a thinning ice sheet reducing the closing force. Conversely, the subsequent change in ice flow speed steepens the ice sheet, which strengthens the tensile stress. As the ice sheet melts, a third factor also contributes to the crevasses expanding, Colgan said. “Twenty years ago crevasses might have been sitting open exposed to air, but now they are filled with water which forces them open.”

The team then went on to investigate how the crevasse area increase might impact ice sheet sliding. In this study, and a companion study published online September 13 in the Journal of Glaciology, the scientists compared the drainage of water by crevasses and moulins—near-vertical chutes in the ice—and found moulin drainage to be more efficient in moving water to the bed of the ice sheet and promoting sliding. But with the increase in crevasse area, the number of moulins had decreased, Colgan said. “The crevasse fields seem to be absorbing the moulins.”

Previously, scientists had believed that as more ice melts and water accumulates on the surface of the ice sheet, more water drains though the moulin network to the underside of the ice sheet enhancing its slide into the ocean. “For the last ten years popular opinion has been more melt equals more slide into the ocean,” he said. “Some recent papers have speculated that more melt might equal no change in sliding, but ours might be the first paper that says that despite more melt, changes in the way that the water is routed to the bed might equal less slide.”

The team now intends to investigate whether crevasse area has increased Greenland-wide and, if so, determine the impact on ice-sheet sliding. While the study may have identified one previously unrecognized influence on ice-sheet dynamics, Colgan cautions it is just one of many factors which determine the iceberg calving rate. “The recent trend of increasing iceberg calving rates is unlikely to be reversed by a potential decrease in sliding, as the majority of ice movement comes from flow rather than sliding,” he said.

The study “An increase in crevasse extent, West Greenland: Hydrologic implications” was funded by the National Aeronautics and Space Administration and the National Science Foundation. Coauthors include CIRES Director Konrad Steffen, CIRES student W. Scott McLamb and CIRES Fellow Waleed Abdalati. Collaborators on the project include the Aerospace Engineering and Sciences and Civil, Environmental, and Architectural Engineering departments at the University of Colorado Boulder, the Institute of Arctic and Alpine Research at the University of Colorado Boulder and the Geophysical Institute of the University of Alaska Fairbanks.

CIRES graduate student, Daniel McGrath led the study published in the Journal of Glaciology “Assessing the summer water budget of a moulin basin in the Sermeq Avannarleq ablation region, Greenland Ice Sheet.” Coauthors of this study include William Colgan and Konrad Steffen. Collaborators on the project include the Aerospace Engineering Sciences Department at the University of Colorado Boulder and the Extreme Ice Survey, Boulder.

William Colgan, CIRES, 303-735-3681,

Konrad Steffen, CIRES, 303-492-8773,

Karin Vergoth, CIRES, 303-497-5125,

The black smoke that rose from the water’s surface during controlled burns of surface oil from the Deepwater Horizon oil spill last year pumped more than one million pounds of black carbon (soot) pollution into the atmosphere, according to a new study published online this week by researchers at Cooperative Institute for Research in Environmental Sciences (CIRES) and NOAA.

This amount is roughly equal to the total black carbon emissions normally released by all ships that travel the entire Gulf of Mexico during a 9-week period, scientists noted.

Black carbon, whose primary component is often called soot, is known to degrade air quality and contribute to warming of the Earth’s atmosphere. The new study, published online this week in Geophysical Research Letters, provides some of the most detailed observations made of black carbon sent airborne by burning surface oil.

“Scientists have wanted to know more about how much black carbon pollution comes from controlled burning and the physical and chemical properties of that pollution. Now we know a lot more,” said lead author Anne Perring, a scientist with CIRES and the Chemical Sciences Division of NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colo.

During the 2010 Gulf oil spill, an estimated one of every 20 barrels of spilled oil was deliberately burned off to reduce the size of surface oil slicks and minimize impacts of oil on sensitive shoreline ecosystems and marine life. In response to the spill, NOAA quickly redirected its WP-3D research aircraft to survey the atmosphere above the spill site in June. During a flight through one of the black plumes, scientists used sophisticated instrumentation on board to characterize individual black carbon particles. NOAA’s single particle soot photometer was key to making the black carbon measurements.

Black carbon is the most light-absorbing airborne particle in the atmosphere and the reason for the black color in the smoky plumes that rise from the surface oil fires. Black carbon can also cause warming of the atmosphere by absorbing light. Prolonged exposure to breathing black carbon particles from human and natural burning sources is known to cause human health effects.

During the 9 weeks active surface oil burning, an total of 1.4 to 4.6 million pounds (0.63 to 2.07 million kilograms) of black carbon was sent into the atmosphere of the Gulf of Mexico, the study estimated.

The study also found that the hot soot plumes from the controlled burns reached much higher into the atmosphere than ship emissions normally rise, potentially prolonging the amount of time the black carbon can remain in the atmosphere which would affect where the black carbon end up.

The researchers also found that the average size of the black carbon particles was much larger than that emitted from other sources in the Gulf region, and that the emitted particles produced were almost all black carbon, unlike other sources such as forest fires that tend to produce other particles along with black carbon.

“The size and makeup of the black carbon particles determine how fast the particles are removed from the atmosphere by various processes, which ultimately affects their impact on climate,” says Perring. Larger particles are removed from the atmosphere more quickly and thus have smaller climate impacts. And, those same properties of black carbon are important for assessing human health impacts.

Finally, Perring and her colleagues found that of the oil that was burned, 4 percent of the mass was released as black carbon, an important metric rarely observed during cleanup of an oceanic oil spill, which could help guide future decision-making.

The new paper, Characteristics of Black Carbon Aerosol from a Surface Oil Burn During the Deepwater Horizon Oil Spill, has 15 co-authors from NOAA ESRL and CIRES and can be found on the the Geophysical Research Letter website.


Anne Perring, CIRES,

Karin Vergoth, CIRES, 303-497-5125,

The annual hole in the Antarctic ozone layer could show initial signs of recovery within 10 years, according to a new analysis of 25 years of data collected by scientists from the Cooperative Institute for Research in Environmental Sciences (CIRES) and NOAA at the South Pole.

The scientists have long tracked ozone levels high in the Antarctic atmosphere with balloon-borne instruments, keeping an eye on the annual springtime opening and closing of the ozone hole.

The ozone layer protects Earth from some damaging incoming solar radiation; an ozone hole allows more incoming radiation to hit the surface, elevating the risk of skin cancer, crop damage, and other environmental impacts.

The research team – led by Birgit Hassler a scientist at CIRES and NOAA’s Earth System Research Laboratory in Boulder, Colo. – analyzed the rates at which springtime chemical reactions ate away the ozone above the South Pole during the last 25 years.

The team related those “ozone loss rates” to the atmosphere’s levels of ozone-depleting chemicals, which are declining in abundance because of the international Montreal Protocol agreement to protect the ozone layer.

Projecting that relationship into the future, the research team calculated that between 2017 and 2021, the South Pole data will show that ozone is not being lost as quickly during the spring – an early sign that the Antarctic ozone hole is healing.

The research was published online Thursday in the Journal of Geophysical Research.

WHAT: Availability of scientist to discuss ozone loss paper

WHO: Birgit Hassler, CIRES scientist, lead author

Karin Vergoth, CIRES, 303-497-5125,

While climate change will not modify the extent or frequency of El Niño variability in the next 100 years, the environmental consequences of such events may become more extreme, according to a new collaborative study between scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES) and the National Center for Atmospheric Research (NCAR).

"Based on the latest state-of-the-art model, it does not appear that the warm water/cold water anomaly in the Pacific—known as El Niño and La Niña—is changing," said study coauthor Baylor Fox-Kemper, a CIRES Fellow and assistant professor at the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder. "But due to a warmer and moister atmosphere the impacts of El Niño are changing even though El Niño itself doesn't change."

El Niño events—anomalous warming of the surface water of the eastern and central Pacific Ocean, occurring every four to 12 years—typically coincide with atmospheric changes like reduced trade winds and a displaced jet stream, which can cause unusual weather patterns such as flooding or droughts. These weather patterns can have dire consequences: "Tens of billions of dollars are associated with big El Niño events or La Niña events," Fox-Kemper said.

Advance knowledge of variations in El Niño behavior would allow a community to better prepare, for example, by altering planting seasons or water usage, Fox-Kemper said. "We would like to ask questions such as whether the flooding that occurred in Australia will happen more or less often over the next 100 years," he said. "If one of the impacts of climate change is a changing El Niño, we would like to know as soon as possible so we could start planning."

To determine whether El Niño may become stronger or more frequent in a warming climate, and whether the impacts of El Niño may change, the researchers used the most recent and advanced climate model available from NCAR—the latest version of the Community Climate System Model that scientists are using for the experiments that will inform the next Intergovernmental Panel on Climate Change (IPCC). They compared the model reproductions of variability in ocean surface temperature in the 20th century with model simulations that extended into the 21st century, and found that the changes were not significant. The study was published online in September in the Journal of Climate.

The impacts of El Niño, however, were affected by a warming climate, Fox-Kemper said. "What we see is that certain atmospheric patterns, such as the blocking high pressure south of Alaska typical of La Niña winters, strengthen in the model in the future climate as compared to the 20th century," he said. "So, the cooling of North America expected in a La Niña winter would be stronger in future climates."

Moreover, Fox-Kemper cautions that although El Niño does not appear to be changing in the short-term, it may change in the future under the influence of current climatic warming. Because the oceans heat up slowly and ocean currents move slowly there is a subsequent time lag before the tropics warm up. This means scientists will have to wait longer to see if there are any changes to El Niño with a changing climate, he said. "Even 100 years from now, ocean warming is still working its way through the system," he said. "This study isn't saying there isn't going to be a change to El Niño—it is just that the adjustment process is still happening."

The National Aeronautics and Space Administration, National Science Foundation, the US Department of Energy and the National Energy Research Scientific Computing Center provided funding for the study "Will there be a significant change to El Niño in the 21st century?" Lead author of the study is CIRES scientist Samantha Stevenson and coauthors on the study include NCAR researchers Markus Jochum, Richard Neale, Clara Deser and Gerald Meehl.

Baylor Fox-Kemper, CIRES, 303-492-0532,
Karin Vergoth, CIRES, 303-497-5125,

Wintertime droughts are increasingly common in the Mediterranean region, and human-caused climate change is partly the cause, according to a new analysis by scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES) and colleagues at NOAA. In the lands surrounding the Mediterranean Sea, 10 of the driest 12 winters since 1902 have struck in just the last 20 years.

“The magnitude of drying that has occurred is too great to be explained by natural variability alone,” said Martin Hoerling of NOAA’s Earth System Research Laboratory in Boulder, Colo., lead author of a paper published online in the Journal of Climate Oct. 27, 2011. “This is not encouraging news for a region that already experiences water stress because it implies natural variability alone is unlikely to return the region’s climate to normal.”

Hoerling’s team uncovered a pattern of increasing wintertime dryness that stretched from Gibraltar to the Middle East. The scientists used observations and climate models to investigate several possible culprits including natural variability, a cyclical climate pattern called the North Atlantic Oscillation (NAO), and climate change caused by greenhouse gases released into the atmosphere during fossil fuel use and other human activities.

Climate change from greenhouse gases explained roughly half the increased dryness of 1902-2010, the team found. This means that other processes – none specifically identified in the new investigation – may also have contributed to increasing drought frequency in the region.

The team also found a surprising coincidence between the observed increase in winter droughts and in the projections of climate models that include known increases in greenhouse gases and aerosols. Both observations and model simulations show a sudden shift to drier conditions in the Mediterranean beginning in the 1970s.

The physical reasons for the relationship between climate change and Mediterranean drought involved sea surface temperatures, the researchers reported. In recent decades, greenhouse-induced climate change has caused somewhat greater warming of the tropical oceans than other ocean regions. That pattern has acted to drive drought-conducive weather patterns around the Mediterranean. The timing of the ocean change coincides closely with the timing of increased droughts, the scientists found.

The Mediterranean has long been identified as a “hot spot” for substantial impact from climate change in the latter decades of this century, because of water scarcity in the region and climate modeling that projects increased risk of drought.

“The question has been whether this projected drying has already begun to occur,” Hoerling said. “The answer is yes, in winter.”

Coauthors on the paper “On the Increased Frequency of Mediterranean Drought” are CIRES Fellow Judith Perlwitz and CIRES scientists Jon Eischeid, XiaoWei Quan,Tao Zhang, Philip Pegion.

Judith Perlwitz, CIRES, 303-497-4814, 
Katy Human, CIRES, 303-735-0196,

The sky glow that radiates from cities at night does more than obscure the stars—it also impacts daytime air pollution levels, according to new research from the Cooperative Institute for Research in Environmental Sciences (CIRES).

“This is the first time that this effect has been quantified,” said CIRES scientist Harald Stark, the lead author. “Previously, it was unknown if city lights could influence air pollution.” They do so by breaking down a compound called the nitrate radical that naturally helps cleanse the atmosphere. Acting as a “janitor” of the night sky, the nitrate radical scrubs away air pollutants such as volatile organic compounds that would otherwise form smog and ozone. The cleansing compound only works nightshifts, however, since sunlight destroys the light-sensitive molecule. But the new data reveal that urban lights in cities like Los Angeles are bright enough to also destroy the nitrate radical, decreasing levels by up to 4 percent in the skies over L.A.

The researchers report an encouraging finding, however. Although artificial lights break down the nitrate radical into nitrogen dioxide—an essential molecule for ozone production—it appears from model simulations that this has only a small effect on next-day levels of ozone, one of the major types of air pollutants. “One reason for this is that ozone doesn’t depend linearly on nitrogen compounds,” Stark said. “Other factors such as sunlight, volatile organic compounds and the amount of mixing between layers of the atmosphere also affect ozone production.” Another reason for the small effect could be that the model may have underestimated the impact of nitrate-radical loss on ozone production, Stark said. More detailed model calculations in the future could give more precise answers.

Still, “An important point to keep in mind is that even small changes in ozone levels may decide whether cities are below or above regulatory levels,” Stark said.
Stark and his team flew several nighttime flights over L.A. in May and June 2010, measuring light intensities and concentrations of nitrogen compounds and ozone. They presented some of the initial results at the 2010 American Geophysical Union Fall Meeting and published the full results of their study as a Correspondence article in the November 2011 issue of Nature Geoscience.

The study also assessed the likelihood of urban lights elsewhere in the world altering nitrogen chemistry. Cities such as Chicago, Las Vegas, Valencia, New York City and Tokyo are much brighter than L.A., and the researchers’ calculations show that their nighttime glare likely degrades the nitrate radical at a much higher rate than above L.A., with unknown consequences to air quality.

The data come on the heels of other research showing that light pollution carries other negative effects, such as harming human health by upsetting circadian rhythms, disrupting animal behavior and wasting energy and money for misdirected lighting that shines into the night sky. Methods for reducing light pollution include using shielded light fixtures that direct the light to the ground, rather than into the sky; and intelligent lights that only switch on when they are needed.

Stark and his team next plan to study other cities with brighter lights (such as Chicago) and more pollution (like Beijing) to quantify how much nitrate-radical loss affects air pollution in these locations. Such research could help inform decision makers on new and better ways to improve air quality.

NOAA Climate Change and NOAA Health of the Atmosphere provided funding for the study.

Harald Stark, 303-492-0840,

Karin Vergoth, CIRES,, 303-497-5125

The Green Data Center Team at the National Snow and Ice Data Center (NSIDC), part of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder, has received the Colorado 2011 Governor's Award for High-Impact Research. The team was recognized for its innovative data center redesign that slashed energy consumption for data center cooling by more than 90%, demonstrating how other data centers and the technology industry can save energy and reduce carbon emissions.

The Green Data Center went online in summer 2011. The heart of the design includes new cooling technology that uses a fraction of the energy required by traditional air conditioning. The second phase of the project, to be completed in late 2011, includes an extensive rooftop solar array that will result in additional energy savings. The design team was led by NSIDC technical services manager David Gallaher, in collaboration with several Colorado-based companies and the National Renewable Energy Laboratory (NREL).

Researchers around the world who study Earth's snow, ice, and climate, access data from NSIDC's active data archive, a bank of computers and storage devices that require a cool environment to operate. The machines themselves generate heat. "Even in the dead of winter, our computer room air conditioners were cranking full tilt trying to chill off the 100-degree-plus heat coming off the back of these units," Gallaher said.

Just cooling NSIDC's computer room used to require over 300,000 kilowatt-hours of energy per year, enough to power 34 homes. "There was a certain irony that here we are working on climate research and our data center was consuming an awful lot of power," Gallaher said.

The Green Data Center design takes advantage of Boulder's arid climate. "We're using a new technology called indirect evaporative cooling," Gallaher said. These units, manufactured by Coolerado Corporation, cool by blowing air over water, using much less energy than compressors. Unlike traditional evaporative cooling, indirect evaporative cooling does not add humidity to the room, maintaining the dry environment that computers need.

Smart control technology also saves energy. During much of the year, the system cools the data center by pulling in and filtering outdoor air. On hot days, the new cooling units automatically step in. The solar array will normally feed energy back into the electrical grid, further reducing the center's net carbon footprint. In case of a power outage, the solar array will charge the batteries that provide NSIDC's emergency power supply.

"The technology works, and it shows that others can do this too," Gallaher said. "Data centers are big consumers of energy, and a lot of it is for cooling." According to the U.S. Environmental Protection Agency (EPA), as of 2006, U.S. data centers were estimated to consume 61 billion kilowat- hours of electricity, equivalent to the electricity consumed by 5.8 million average U.S. households. By 2020, the carbon footprint of data centers will exceed that of the airline industry.

NSIDC received a grant for the project from the National Science Foundation (NSF) under its Academic Research Infrastructure Program, with additional support from NASA. NSIDC, which is supported entirely by federal research funding, manages scientific data from NSF field programs and from NASA's Earth Observing System remote sensing program.

The Green Data Center was conceived when NSIDC faced an expensive replacement of its aging, ailing computer room air conditioners. The new evaporative cooling units not only save energy, but offer lower cost of maintenance.

The Governor's Award for High-Impact Research recognizes innovations by Colorado's federally sponsored science and technology laboratories that have made significant impacts beyond the labs. Colorado Governor John Hickenlooper will present the award during a reception at the LEEDS Platinum-certified Xcel Energy building in downtown Denver on November 15th.

The Green Data Center team includes David Gallaher, NSIDC Director Mark Serreze, and Ronald Weaver from NSIDC; Rick Osbaugh from RMH Group in Denver; Otto Van Geet from the National Renewable Energy Laboratory (NREL); and Lee Gillan from Coolerado Corporation.

For more information on NSIDC's Green Data Center, including a monitor of computing center energy usage and cooling, visit

NSIDC supports research into Earth's frozen regions, including sea ice, snow cover, glaciers, ice caps, ice sheets, permafrost, and climate interactions. NSIDC performs scientific research, manages and distributes scientific data, and educates the public. For more information, visit

The 2011 Governor's Award for High Impact Research is sponsored by CO-LABS.

CO-LABS Press Release

University of Colorado Boulder Press Release

Jane Beitler
National Snow and Ice Data Center
University of Colorado Boulder

Elizabeth Lock
University of Colorado Boulder
Media Relations

CIRES Director Konrad Steffen has been named a Fellow of the American Association for the Advancement of Science (AAAS).

Election as a AAAS Fellow is an honor bestowed upon AAAS members by their peers. This year AAAS has awarded 539 members this honor because of their scientifically or socially distinguished efforts to advance science or its applications. New Fellows will be presented with an official certificate and a gold and blue (representing science and engineering, respectively) rosette pin on Saturday, 18 February from 8 to 10 a.m. at the AAAS Fellows Forum during the 2012 AAAS Annual Meeting in Vancouver, B.C., Canada.

Former CIRES Fellow Pieter Tans, currently a senior scientist in NOAA's Climate Monitoring and Diagnostics Laboratory also received the honor. This year's AAAS Fellows will also be formally announced in the AAAS News and Notes section of the journal Science on 23 December 2011.

The amount of air pollutants in the atmospheric plume generated by the Deepwater Horizon oil spill was similar to those generated by a large city according to a new study led by scientists at the Cooperative Institute for Research in Environmental Sciences and NOAA.

The researchers focused on ozone and particulate matter—two pollutants with human health effects and published their results in a recent special issue of Proceedings of the National Academy of Sciences.

About eight percent, or about one of every 13 barrels of the Deepwater Horizon-spilled oil that reached the ocean surface, eventually made its way into airborne organic particles small enough to be inhaled into human lungs, and some of those particles likely reached the Gulf Coast when the winds were blowing toward the shore, according to the study.

"We could see the sooty black clouds from the burning oil, but there’s more to this than meets the eye. Our instruments detected a much more massive atmospheric plume of almost invisible small organic particles and pollutant gases downwind of the oil spill site," said Ann M. Middlebrook, scientist at NOAA ESRL’s Chemical Sciences Division (CSD) and lead author of the study.

According to the study, over the course of the spill, the total mass of organic particles formed from evaporating surface oil was about ten times bigger than the mass of soot from all the controlled burns. Controlled burns are used to reduce the size of surface oil slicks and minimize impacts of oil on sensitive shoreline ecosystems and marine life.

The organic particles formed in the atmosphere from hydrocarbons that were released as surface oil evaporated, and they got bigger as they traveled in the plume. The atmospheric plume was about 30 kilometers wide—about 18.5 miles—when it reached the coast.

Some of the hydrocarbons from the evaporating oil reacted with nitrogen oxides in the atmosphere to create ozone pollution, but this other atmospheric plume was only 3 to 4 kilometers (2 to 3 miles) wide at the coast.

“The levels of ozone were similar to what occurs in large urban areas. During the oil spill, it was like having a large city’s worth of pollution appear out in the middle of the Gulf of Mexico,” said Daniel M. Murphy, NOAA scientist at ESRL/CSD and a co-author of the study.

The relatively small amounts of nitrogen oxides in the vicinity of the oil spill (which included nitrogen oxides emitted by the spill cleanup and recovery efforts) limited the amount of polluting ozone that was formed offshore. When the excess hydrocarbons reached the coast, they could have reacted with onshore sources of nitrogen oxides, such as cars and power plants, to form additional ozone.

The researchers gathered data in June 2010 on two flights of NOAA’s WP-3D research aircraft that was outfitted to be a “flying chemical laboratory.” They also analyzed data gathered on ships in the vicinity and at two monitoring sites in Mississippi downwind of the oil spill.

They used a regional air quality model to project the path of the particle pollution, and found that time periods when the pollution plume was predicted to have reached the coast matched up well with a few short periods of high readings at the monitoring sites.

In addition to the organic particles that formed from the evaporating oil, soot particles were lofted into the atmosphere from the oil that was burned on the surface.

The authors noted that their findings could help air quality managers anticipate the effects of future oil spills. The depth of the Deepwater Horizon spill, about a mile beneath the surface, limited the effects on air quality because some hydrocarbons, such as benzene, largely dissolved in the water.

“It was fortunate that the effects on air quality of the Deepwater Horizon oil spill were limited in scope,” said Middlebrook. “Our findings show that an oil spill closer to populated areas, or in shallower waters, could have a larger effect.”

The new paper, "Air Quality Implications of the Deepwater Horizon Oil Spill," has 25 co-authors from NOAA ESRL and CIRES. For more information, visit the Proceedings of the National Academy of Sciences website.

Katy Human, CIRES,, 303-735-0196

Study shows less hail, more rain in region’s future, with possible increase in flood risk

Summertime hail could all but disappear from the eastern flank of Colorado’s Rocky Mountains by 2070, according to a new modeling study by scientists from the Cooperative Institute for Research in Environmental Sciences (CIRES), NOAA and several other institutions.

Less hail damage could be good news for gardeners and farmers, said lead author Dr. Kelly Mahoney, a research scientist at CIRES, but a shift from hail to rain can also mean more runoff, which could raise the risk of flash floods.

“In this region of elevated terrain, hail may lessen the risk of flooding because it takes awhile to melt,” Dr. Mahoney said. “Decision makers may not want to count on that in the future.”

For the new study, published this week in the journal Nature Climate Change, Dr. Mahoney and her colleagues used “downscaling” techniques to try to understand how climate change might affect hail-producing weather patterns across Colorado.

The research focused on storms involving relatively small hailstones (up to pea-sized) on Colorado’s Front Range, a region that stretches from the foothill communities of Colorado Springs, Denver and Fort Collins up to the Continental Divide. Colorado’s most damaging hailstorms tend to occur further east and involve larger hailstones not examined in this study.

In the summer in Colorado’s Front Range above about 7,500 feet, precipitation commonly falls as hail. Decision makers concerned about the safety of mountain dams and flood risk have been interested in how climate change may affect the amount and nature of precipitation in the region.

Dr. Mahoney and her colleagues began exploring that question with results from two climate models, which assumed that levels of climate-warming greenhouse gases will continue to increase in the future, from about 390 ppm today to 620 ppm in 2070.

But the weather processes that form hail – thunderstorm formation, for example – occur on much smaller scales than can be reproduced by global climate models. So the team “downscaled” the global model results twice: first to regional-scale models that can take regional topography and other details into account (this step was completed as part of the National Center for Atmospheric Research’s North American Regional Climate Change Assessment Program.) Then, the regional results were downscaled to weather-scale models that can resolve individual storms and even the in-cloud processes that create hail. 

Finally, the team compared the hailstorms of the future (2041-2070) to those of the past (1971-2000) as captured by the same sets of downscaled models. Results were similar in experiments with both climate models. 

“We found a near elimination of hail at the surface,” Mahoney said.

In the future, increasingly intense storms may actually produce more hail inside clouds, the team found. However, because those relatively small hailstones fall through a warmer atmosphere, they melt quickly, falling as rain at the surface or evaporating back into the atmosphere. In some regions, simulated hail fell through an additional 1,500 feet (~450 m) of above-freezing air in the future, compared to the past. 

The research team also found evidence that precipitation events over Colorado become more extreme in the future, while changes in hail may depend on the size of the hail stones - results that will be explored in more detail in ongoing work. 

Dr. Mahoney’s postdoctoral research was supported by the PACE program (Postdocs Applying Climate Expertise) administered by the University Corporation for Atmospheric Research and funded by CIRES Western Water Assessment, NOAA, and the U.S. Bureau of Reclamation. PACE connects young climate scientists with real-world problems such as those faced by water resource managers.

Co-authors of the new paper, “Changes in hail and flood risk in high-resolution simulations over the Colorado Mountains,” include James Scott and Joseph Barsugli (CIRES/NOAA), Michael Alexander (NOAA/Earth System Research Laboratory) and Gregory Thompson (National Center for Atmospheric Research).

Kelly Mahoney, CIRES, 
Katy Human, CIRES, 303-735-0196,