Friday, May 16th 10:30am - 12:30pm
Russell Senate Office Building
What are black carbon (BC) aerosols and Atmospheric Brown Clouds (ABC), and in what way to they exacerbate or add to air pollution and global and regional climate warming? What is the scale of the problem? Are there indirect affects of BC and ABC as well? Which regions of the U.S., Asia and rest of the world seem most affected by BC and ABC? What are these affects and how do these intersect and interact with greenhouse gases and global warming? Are there policy opportunities? Is there now a scientific basis for a direct causal link between CO2 emissions and health? From the perspective of air pollution, does controlling carbon dioxide have a robust scientific basis?
Dr. Anthony Socci, Senior Science Fellow, American Meteorological Society
Dr. Mark Z. Jacobson, Professor of Civil and Environmental Engineering; Professor by Courtesy of Energy Resources Engineering; Director, Atmosphere/Energy Program; and Senior Fellow by Courtesy, Woods Institute for the Environment, Stanford University, Stanford, CA
Jacobson PowerPoint HTML Version
Dr. V. Ramanathan, Distinguished Professor of Climate and Atmospheric Sciences, Victor C. Alderson Professor of Applied Ocean Sciences Chairman, Atmospheric Brown Clouds Project (UNEP Sponsored) Director, Center for Clouds, Chemistry and Climate, Scripps Institution of Oceanography, University of California, San Diego, CA
Ramanathan PowerPoint HTML Version
Contribution of Black Carbon and Atmospheric Brown Clouds to Climate Warming: Impacts and Opportunities
Black carbon (BC) in soot is the dominant absorber of visible solar radiation in the atmosphere. Anthropogenic sources of black carbon, although distributed globally, are most concentrated in the tropics where solar irradiance is highest. Black carbon is often transported over long distances, mixing with other aerosols along the way. The aerosol mix can form transcontinental plumes of atmospheric brown clouds (ABCs), with vertical extents of 1.8 to 3.1 miles. Because of the combination of high absorption, a regional distribution roughly aligned with solar irradiance, and the capacity to form widespread atmospheric brown clouds in a mixture with other aerosols, emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions. In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide (CO2) in the melting of snowpacks and glaciers. The interception of solar radiation by atmospheric brown clouds leads to dimming at the Earth’s surface with important implications for the hydrological cycle, and the deposition of black carbon darkens snow and ice surfaces, which can contribute to melting, in particular of Arctic sea ice. Presently, populations on the order of 3 billion people are living under the influence of regional ABC hotspots.
Black carbon (BC) is an important part of the combustion product commonly referred to as soot. BC in indoor environments is largely due to cooking with biofuels such as wood, dung and crop residue. Outdoors, it is due to fossil fuel combustion (diesel and coal), open biomass burning (associated with deforestation and crop residue burning), and cooking with biofuels.
Soot aerosols absorb and scatter solar radiation. BC refers to the absorbing components of soot. Dust, which also absorbs solar radiation, is not included in the definition of BC. Globally, the annual emissions of BC are (for the year 1996) roughly 8.8 tons per year, with about 20% from biofuels, 40% from fossil fuels and 40% from open biomass burning. The uncertainty in the published estimates for BC emissions is a factor of two to five on regional scales and at least ±50% on global scales. High BC emissions occur in both the northern and the Southern Hemisphere, resulting largely from fossil fuel combustion and open burning, respectively.
Atmospheric brown clouds are composed of numerous submicrometer aerosols, including BC, but also sulphates, nitrates, fly ash and others. BC is also internally mixed with other aerosol species such as sulphates, nitrates, organics, dust and sea salt. BC is removed from the atmosphere by rain and snowfall. Removal by precipitation, as well as direct deposition to the surface, limits the atmospheric lifetime of BC to about one (±1) week.
Given that BC has a significant contribution to global climate warming, and a much shorter lifetime compared with CO2 (which has a lifetime of 100 years or more), a major focus on decreasing BC emissions offers an opportunity to mitigate the effects of global warming trends in the short term. Reductions in BC are also warranted from considerations of regional climate change and human health.
Causal Link between Carbon Dioxide and Air Pollution Mortality
Recent research suggests that carbon dioxide, through its increase in temperatures and water vapor, increases U.S. air pollution deaths. This effect is greatest in locations where air pollution is already high. The causes of the increased death rate are increased respiratory illness, cardiovascular diseases, and complications from asthma due to increases in ozone and particulate matter. Ozone increases with more carbon dioxide because, in urban areas, higher temperatures and water vapor independently increase ozone through enhanced chemical reactions. These effects are not so important in rural areas. However, in rural areas, higher temperatures increase organic gas emissions from vegetation, increasing ozone slightly. Particles increase with more carbon dioxide because carbon dioxide increases air temperatures more than ground temperatures, reducing vertical and horizontal dispersion of pollutants. Furthermore, water vapor from carbon dioxide’s warming increases humidity, causing particles to swell and absorb more pollutant gases. Finally, more organic gases from vegetation result in more sticky gases that convert to particles.
It now appears that an estimated 1000 (350-1800) additional people die per year in the U.S. per 1 degree Celsius of temperature rise due to carbon dioxide. To date, global temperatures have increased by 0.8 degrees Celsius due to carbon dioxide and other greenhouse gases and absorbing particles. The same effect should hold for other greenhouse gases. This incremental death rate compares with a current air pollution death rate of 50,000-100,000 per year in the U.S. California is especially hard hit because it has 6 of the 10 top polluted cities in the U.S. California was found to suffer 30% or more of the additional fatalities due to carbon dioxide although it has only 12% of the U.S. population.
Recently, the U.S. EPA denied California’s request to permit the state to regulate carbon dioxide on its own, in part, on the premise that California did not have a special circumstance relative to other states; no studies had isolated carbon dioxide’s effect (as opposed to all greenhouse gases) on air pollution; and no studies had quantified the health impacts of carbon dioxide. The research described herein may well present an opportunity for EPA to revisit its original ruling in light of these more recent scientific findings.
Dr. V. Ramanathan is the Distinguished Professor of Atmospheric and Climate Sciences at the Scripps Institution of Oceanography, University of California at San Diego. In the mid 1970s he discovered the greenhouse effect of CFCs and numerous other manmade trace gases. He correctly forecasted in 1980, along with R. Madden, that the global warming due to carbon dioxide would be detectable by the year 2000. He also used satellite radiometers to detect the atmospheric greenhouse effect and showed that clouds had a large natural cooling effect on the planet. He, along with Nobel Prize-Winning chemist, Dr Paul Crutzen, led the Indian Ocean Experiment (INDOEX) that first discovered the widespread South Asian Atmospheric Brown Clouds (ABCs). Using INDOEX, Dr. Ramanathan showed that the South Asian brown clouds led to large scale dimming of the ocean, slowed down the monsoon circulation and decreased monsoon rainfall. He followed this with a path-breaking study with agricultural economists to show that ABCs and greenhouse gases were responsible for a 14% decrease in rice harvest in India. More recently, he used miniaturized instruments on light weight unmanned aircraft to show that black carbon in ABCs are causing a large heating of the atmosphere over Asia, linking ABCs to the melting of Himalayan and Tibetan glaciers.
Dr. Ramanathan currently chairs the UNEP-sponsored ABC Project with science team members from the USA, Europe, India, China, Japan, Korea and other Asian countries. He is the recipient of many national and international awards such as: the American Meteorological Society’s Rossby medal, induction into the American Philosophical Society, induction into the US National Academy of Sciences and induction into the Pontifical Academy of Sciences by Pope John Paul II. He currently chairs the US National Academy of Sciences panel that provides strategic advice to the US Climate Change Science Program (CCSP) which is a $2 billion/year inter-agency research program on climate change.
Dr. Ramanathan has published over 175 peer-reviewed articles in major journals such as Nature, Science, Proceedings of the National Academy of Sciences, Journal of Geophysical Research, among others, and in books and UN reports. He has also contributed to the Intergovernmental Panel on Climate Change since its inception, and served as one of the lead editors in IPCC-AR4 (2007), WG-I. He received his undergraduate and graduate education in India and earned his Ph. D. in planetary atmospheres from the State University of New York at Stony Brook.
Dr. Mark Z. Jacobson is Director of the Atmosphere/Energy Program and Professor of Civil and Environmental Engineering at Stanford University. He is also Professor of Energy Resources Engineering and Senior Fellow of the Woods Institute for the Environment, by courtesy. He received a B.S. in Civil Engineering with distinction, an A.B. in Economics with distinction, and an M.S. in Environmental Engineering from Stanford University, in 1988. He received an M.S. in Atmospheric Sciences in 1991 and a PhD in Atmospheric Sciences in 1994 from UCLA. He has been on the faculty at Stanford since 1994. His work relates primarily to the development and application of numerical models to understand better the effects of air pollutants from energy systems and other sources, on climate and air quality. He also supports work on the mapping and analysis of winds for wind energy. He has published two textbooks, "Fundamentals of Atmospheric Modeling" and "Atmospheric Pollution: History, Science, and Regulation," and over 75 peer-reviewed scientific journal articles. He received the 2005 American Meteorological Society Henry G. Houghton Award for "significant contributions to modeling aerosol chemistry and to understanding the role of soot and other carbon particles on climate." His recent paper, "Effects of ethanol versus gasoline on cancer and mortality in the United States" was the most-accessed article which appeared in the April-September, 2007, issue of the journal, Environmental Science and Technology.
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