Chair's Lecture with V. Ramanathan and Lynn Russell

"Black Carbon Reductions in California and its Implications for Regional and Global Climate Change Mitigation"

Veerabhadran Ramanathan, Ph.D., and Lynn M. Russell, Ph.D., Scripps Institution of Oceanography, University of California, San Diego.

July 23, 2013

Black carbon (BC) is the most strongly light-absorbing component of particulate matter (PM), and is formed by the incomplete combustion of fossil fuels, biofuels, and biomass.  Black carbon contributes to the adverse impacts on human health, ecosystems, and visibility associated with PM2.5. Today’s seminar summarizes the results of two research projects on assessment of the impact of BC on the regional radiative forcing and climate trends of California.

Dr. Ramanathan will present the principal findings and implications resulting from a three year multi-institutional regional integrated assessment of the climate and air pollution effects of black carbon. It is the first such attempt to estimate the radiative forcing of BC for California, both from a bottom-up approach (starting with emission inventory as input to aerosol-transport models) and a top-down approach (adopting satellite data in conjunction with ground based column averaged aerosol optical properties). This approach reveals three unanticipated major findings:

  1. the first finding concerns the large decadal trends in BC concentrations largely in response to policies enacted to decrease PM emissions from diesel combustion;
  2. the second is the finding that the climate cooling effects of reductions in black carbon were not offset by reductions in organic and sulfate particles; and
  3. the discovery of the large effects of brown carbon (a form of organic carbon aerosols) on radiative forcing.

The major implication of this study is that reductions in emissions of BC mostly from diesel engines, since the 1980s have contributed to a measurable mitigation of anthropogenic global warming, equivalent to the mitigation of 21 million metric tons of CO2 emissions annually and could be as high as 50 million tons annually. Because of the long lifetime of CO2 (one century or longer) compared with the much shorter lifetime of BC (about one week), mitigation of CO2 is critical for limiting long term global warming, while mitigation of BC is critical for limiting near-term warming.

Dr. Russell will discuss the relative importance of the first indirect aerosol effect of BC forcing for California’s climate. BC particles could also indirectly cause changes in the absorption or reflection of solar radiation through changes in the properties and behavior of clouds.  The results of the study show that reducing BC particle concentration by 50% decreased the cloud droplet concentration by between 6% and 9% resulting in the formation of fewer, larger cloud droplets that correspond to a lower cloud albedo. The implications of this comparison are that in addition to total number concentration, the size and composition of BC-containing particles is also a significant factor in determining the net impact on clouds. For regions like California, where BC mitigation targets primarily fossil fuel sources, the cloud albedo effect of BC particles may partially offset the climate benefits of direct forcing reduction. But the cloud-burning effects of BC can enhance the climate benefits of direct forcing reduction, having the opposite effect.

Speaker Biographies

Veerabhadran Ramanathan, Ph.D., is Victor Alderson Professor of Applied Ocean Sciences and Director of the Center for Atmospheric Sciences at the Scripps Institution of Oceanography, University of California, San Diego and UNESCO Professor of Climate and Policy, TERI University, Delhi, India. Dr. Ramanathan discovered the strong greenhouse effect of CFCs in 1975 and along with Roland Madden, predicted in 1980 that global warming would be detected by 2000. In 1985 he led the first international NASA/WMO/UNEP assessment on the climate effects of non-CO2 greenhouse gases and concluded that they are as important as CO2 to global climate change. Dr. Ramanathan's recent finding is that mitigation of short lived climate pollutants (black carbon, methane, ozone and HFCs) will slow down global warming significantly during this century. This proposal has now been adopted by UNEP and 12 countries including the USA. Dr. Ramanathan now leads Project Surya which is mitigating black carbon and other climate warming emissions from solid biomass cooking in South Asia and Kenya and is documenting their effects on public health and environment. In 2012 he was honored by Pope Benedict with an appointment to the Council of the Pontifical Academy of Sciences and UNESCO awarded the Climate and Policy professorship at TERI Deemed-University in New Delhi, India. Dr. Ramanathan is co-organizer of a 2014 Vatican meeting on “Sustainable Humanity, Sustainable Nature” of social and natural scientists, philosophers and policy makers,

Lynn M. Russell, Ph.D., is Professor of Atmospheric Chemistry at Scripps Institution of Oceanography, University of California at San Diego, where she has led the Climate Sciences Curricular Group since 2009. Dr. Russell's research is in the area of aerosol particle chemistry, including the behavior of particles from both biogenic and combustion processes. Her research group pursues both modeling and measurement studies of atmospheric aerosols, using the combination of these approaches to advance our understanding of fundamental processes that affect atmospheric aerosols. She served on the faculty of Princeton University in the Department of Chemical Engineering before accepting her current position at Scripps in 2003. She has been honored with young investigator awards from ONR, NASA, Dreyfus Foundation, NSF, and the James S. McDonnell Foundation, and she received the Kenneth T. Whitby Award from AAAR (2003) for her contributions on atmospheric aerosol processes and the Princeton Rheinstein Award for excellence in teaching and scholarship (1998).

More Information

The Chair of the California Air Resources Board invites guests to speak on environmental subjects involving air pollution and global warming. Find additional lectures on the Chair's Lecture Series webpage.