The lingering clouds: Why pollution results in larger storm clouds, colder days, warmer nights

A new study reveals how pollution causes thunderstorms to leave behind larger, deeper, longer lasting clouds. Appearing in the Proceedings of the National Academy of Sciences November 26, the results solve a long-standing debate and reveal how pollution plays into climate warming. The work can also provide a gauge for the accuracy of weather and climate models.

Researchers had thought that pollution causes larger and longer-lasting storm clouds by making thunderheads draftier through a process known as convection. But atmospheric scientist Jiwen Fan and her colleagues show that pollution instead makes clouds linger by decreasing the size and increasing the lifespan of cloud and ice particles. The difference affects how scientists represent clouds in climate models.

"This study reconciles what we see in real life to what computer models show us," said Fan of the Department of Energy's Pacific Northwest National Laboratory. "Observations consistently show taller and bigger anvil-shaped clouds in storm systems with pollution, but the models don't always show stronger convection. Now we know why."

Also, pollution can decrease the daily temperature range via such clouds: High clouds left after a thunderstorm spread out across the sky and look like anvils. These clouds cool the Earth during the day with their shadows but trap heat like a blanket at night. Pollution can cause clouds from late afternoon thunderstorms to last long into the night rather than dissipate, causing warmer nights.

Secret Life of Clouds

Models that predict weather and climate don't reconstruct the lives of clouds well, especially storm clouds. Usually these models replace storm clouds with simple equations that fail to capture the whole picture.

Because of the poor reconstructions, researchers have been faced with a dilemma: Pollution causes the anvil-shaped clouds to linger longer than they would in clean skies -- but why?

Possible reasons revolve around tiny natural and human-made particles called aerosols that serve as seeds for cloud droplets to form around. A polluted sky has many more aerosols than a clean sky -- think haze and smog -- and that means less water for each seed. Pollution makes more cloud droplets, but each droplet is smaller.

More and smaller droplets change things for the clouds. Researchers have long thought that smaller droplets start a chain reaction that leads to bigger, longer-lasting clouds: Instead of raining down, the lighter droplets carry their water higher, where they freeze. The freezing squeezes out the heat the droplets carry with them and causes the thunder cloud to become draftier. The stronger convection lifts more water droplets, building up the cloud.

But researchers don't always see stronger convection every time they see larger and longer-lasting clouds in polluted environments, indicating a piece of the puzzle was missing.

To solve this dilemma, Fan and colleagues decided to compare real-life summer storm clouds to a computer model that zooms deep into simulated clouds. The model included physical properties of the cloud particles as well as the ability to see convection, if it gets stronger or weaker. Most models run in days or weeks, but the simulations in this study took up to six months.

"Modeling the details of cloud microphysical properties is very computationally intensive, so models don't usually include them," said Fan.

Convection Vexation

The researchers started with cloud data from three locations that differ in how polluted, humid and windy they typically are: the tropics in the western Pacific, southeastern China and the Great Plains in Oklahoma. The data had been collected through DOE's ARM Climate Research Facility.

With support from DOE's Regional and Global Climate Model program, the research ran simulations on PNNL's hometown supercomputer Olympus. Their simulations of a month of storms ended up looking very similar to the actual observed clouds, validating that the models re-created the storm clouds well.

The team found that in all cases, pollution increased the size, thickness and duration of the anvil-shaped clouds. However, only two locations -- the tropics and China -- showed stronger convection. The opposite happened in Oklahoma -- pollution made for weaker convection.

This inconsistency suggested that stronger convection isn't the reason. Taking a closer look at the properties of water droplets and ice crystals within clouds, the team found that pollution resulted in smaller droplets and ice crystals, regardless of location.

In addition, the team found that in clean skies, the heavier ice particles fall faster out of the anvil-shaped clouds, causing the clouds to dissipate. However, the ice crystals in polluted skies were smaller and too light to fall out of the clouds, leading to the larger, longer-lasting clouds.

Lastly, the team estimated how much warming or cooling the storm clouds contributed. Overall, the polluted clouds cooled the day and warmed the night, decreasing the daily temperature range.

Most models don't simulate convection well, take into account the microphysical processes of storm clouds, nor address how pollution interacts with those processes. Accounting for pollution effects on storm clouds in this way could affect the ultimate amount of warming predicted for the Earth in the next few decades. Accurately representing clouds in climate models is key to improving the accuracy of predicted changes to the climate.

Journal Reference:

J. Fan, L. R. Leung, D. Rosenfeld, Q. Chen, Z. Li, J. Zhang, H. Yan. Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1316830110

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New report examines national oil pollution threat from shipwrecks

May 20, 2013

14 May, 1942, U. S. Army Air Corps photographs of the burning tanker Potrero del Llano location.

Download here (Credit: Images courtesy of National Archives, College Park, MD )

NOAA presented to the U.S. Coast Guard today a new report that finds that 36 sunken vessels scattered across the U.S. seafloor could pose an oil pollution threat to the nation’s coastal marine resources. Of those, 17 were recommended for further assessment and potential removal of both fuel oil and oil cargo.

The sunken vessels are a legacy of more than a century of U.S. commerce and warfare. They include a barge lost in rough seas in 1936; two motor-powered ships that sank in separate collisions in 1947 and 1952; and a tanker that exploded and sank in 1984. The remaining sites are 13 merchant marine ships lost during World War II, primarily along the Atlantic Seaboard and Gulf of Mexico. To see a list of the ships and their locations, visit: http://sanctuaries.noaa.gov/protect/ppw/.

The report, part of NOAA’s Remediation of Underwater Legacy Environmental Threats (RULET) project, identifies the location and nature of potential sources of oil pollution from sunken vessels. Knowing where these vessels are helps oil response planning efforts and may help in the investigation of reported mystery spills--sightings of oil where a source is not immediately known or suspected. “This report is the most comprehensive assessment to date of the potential oil pollution threats from shipwrecks in U.S. waters,” said Lisa Symons, resource protection coordinator for NOAA’s Office of National Marine Sanctuaries. “Now that we have analyzed this data, the Coast Guard will be able to evaluate NOAA’s recommendations and determine the most appropriate response to potential threats.”

“The Coast Guard is pleased to receive these risk assessments from our partner agency NOAA and looks forward to our continued coordination on the matter of potential pollution associated with sunken vessels in U.S. waters,” said Capt. John Caplis, the Coast Guard’s chief of marine environmental response. “Coast Guard federal on-scene coordinators receiving the risk assessments will carefully review the data and incorporate it into their area contingency plans.”

In 2010, Congress appropriated $1 million for NOAA to develop a list of the most significant potentially polluting wrecks in U.S. waters, including the Great Lakes, specifically addressing ecological and socio-economic resources at risk. Those funds were not intended for oil or vessel removal.

NOAA maintains the internal Resources and UnderSea Threats (RUST) database of approximately 30,000 sites of sunken material, of which 20,000 are shipwrecks. The remaining items are munitions dumpsites, navigational obstructions, underwater archaeological sites, and other underwater resources.

Initial screening of these shipwrecks revealed 573 that could pose substantial pollution risks, based on the vessel’s age, type, and size. This includes vessels built after 1891, when U.S. vessels began using fuel oil; vessels built of steel; vessels over 1,000 gross tons, and any tank vessel.

Additional research about the circumstances of each vessel’s loss narrowed that number to 107 shipwrecks. Of those, some were deemed navigational hazards and demolished, and others were salvaged. Most of the 107 wrecks have not been directly surveyed for pollution potential, and in some cases little is known about their current condition.

To prioritize and determine which vessels are candidates for further evaluation, NOAA used a series of risk factors to assess the likelihood of substantial amounts of oil remaining onboard, and the potential ecological and environmental effects if that oil spills. Risk factors include the total oil volume onboard as cargo or fuel, the type of oil, and the nature of the sinking event. For example, a vessel that was struck by multiple torpedoes would likely contain less oil than a vessel that sank in bad weather.

After this third level of screening, 87 wrecks remained on the list developed for the Coast Guard’s area contingency plans. Among this group, NOAA determined that 36 shipwrecks are candidates for a “Worst Case” discharge event in which the shipwreck’s entire fuel oil and oil cargo would be released simultaneously, and recommended that 17 of these wrecks be considered for further assessment and feasibility of oil removal.

Six wrecks are potential candidates for a “Most Probable” discharge event, where a shipwreck could lose approximately 10 percent of its fuel oil or oil cargo. To date, known oil discharges from shipwrecks are typically in the “Most Probable” category or smaller.

The report, including 87 risk assessments, is not intended to direct Coast Guard activities, but rather provide the Coast Guard with NOAA’s scientific and technical assessment and guidance as a natural resource and cultural heritage trustee.

The Coast Guard, as the federal On-scene Coordinator for mitigating oil spills in the coastal marine environment, the Regional Response Teams, and local Area Committees, as established under the Oil Pollution Act of 1990, will review and incorporate the assessments into regional and area marine environmental response contingency plans. The individual risk assessments not only highlight concerns about potential ecological and socio-economic impacts, but also characterize most of the vessels as historically significant and many of them as grave sites, both civilian and military.

Funding for any assessment or recovery operations determined to be necessary is dependent upon the unique circumstances of the wreck. If a wreck still has an identifiable owner, that owner is responsible for the cost of cleanup. Coast Guard officials say that if no responsible party exists, the Oil Spill Liability Trust Fund would likely be accessed.

To view the report, 2012 Risk Assessment for Potentially Polluting Wrecks in U.S. Waters, visit http://sanctuaries.noaa.gov/protect/ppw/.

As America’s maritime first responder, the Coast Guard protects those on the sea, protects our nation from threats delivered by sea, and protects the sea itself. By executing our marine environmental protection responsibilities, the Coast Guard reduces the risk of harm to the marine environment by developing and enforcing regulations to prevent and respond to maritime oil spills and hazardous substance releases.

NOAA’s mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Join us on Facebook, Twitter and our other social media channels.

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China's pollution costs $112B in health care

China's unprecedented growth is carrying a steadily steeper price tag as its air pollution hikes the nation's health care costs, finds a new study by the Massachusetts Institute of Technology.

Although China has made substantial progress in reducing its air pollution, MIT researchers say its economic impact has jumped from $22 billion in 1975 to $112 billion in 2005. The costs result from both lost labor and the increased need for health care because ozone and particulates in air can cause respiratory and cardiovascular diseases.

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"The results clearly indicate that ozone and particulate matter have substantially impacted the Chinese economy over the past 30 years," Noelle Selin, an assistant MIT professor of engineering systems and atmospheric chemistry, said in announcing the findings that appear in the February edition of the journal Global Environmental Change.

The study, by researchers at the MIT Joint Program on the Science and Policy of Global Change, said pollution's economic impact has grown, because population growth increased the number of people exposed to it and higher incomes raised the costs associated with lost productivity.

The study "finds that the damages are even greater than previously thought," said Kelly Sims Gallagher, an associate professor of energy and environmental policy at Tufts University's Fletcher School, in the MIT announcement.

The researchers calculated these long-term impacts using atmospheric and economic modeling tools, which were especially important when it came to assessing the cumulative impact of ozone. They said China has only recently begun to monitor ozone , and it's become the world's largest emitter of mercury, carbon dioxide and other pollutants.

In the 1980s, they said China's particulate-matter concentrations were at least 10 to 16 times higher than the World Health Organization's annual guidelines. Even after major improvements, by 2005, they said the concentrations were still five times higher than what is considered safe and led to 656,000 premature deaths in China each year.

China is taking steps to mitigate air pollution, in partly by boosting its support for renewable energy sources such as wind and solar. Its hefty subsidies to its solar industry have prompted some U.S. manufacturers to file a complaint with the International Trade Commission. In January, the nation set a target to reduce its 2010 levels of carbon intensity (the amount of carbon emitted per unit of gross domestic product) 17% by 2015.

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