Are the Effects of Black Carbon Overestimated in Climate Models?
Atmospheric black carbon may not cause as much warming of the climate as we thought.
The Science
Two California field campaigns suggest that the warming by black carbon (BC) may be overestimated in climate models.
The Impact
Black carbon in the atmosphere has a strong effect on global and regional climate, but a recent study suggests that the climate benefits of BC mitigation may be overestimated.
Summary
Atmospheric black carbon (BC) warms Earth’s climate, and its reduction has been targeted for near-term climate change mitigation. Some estimates suggest that the positive (warming) radiative forcing by BC is second only to CO2, making it an important near-term climate mitigation target. In a recent study, direct measurements of BC absorption enhancements and average mixing state for BC in the atmosphere around California are reported from two field campaigns: the 2010 CalNex study and DOE’s Carbonaceous Aerosols and Radiative Effects Study (CARES). The CalNex measurements were made onboard the R/V Atlantis, whereas the CARES measurements were made at a ground site in the Sacramento urban area. Observations indicate that the BC absorption enhancements for ambient particles around large urban centers do not vary much with photochemical aging, are significantly less than predicted from traditional theory, and are in contrast to laboratory experiments. Further, they indicate a role for absorption at short visible wavelengths by non-BC aerosol components [brown carbon (BrC) in urban environments] which are not well quantified in current measurements or models.
Contact
Dr. Christopher Cappa
University of California at Davis
[email protected]
Funding
Basic Research: DOE Office of Science, Office of Biological and Environmental Research
Publications
Christopher D. Cappa et al. Radiative Absorption Enhancements Due to the Mixing State of Atmospheric Black Carbon, Science 337, 1078 (2012); [DOI: 10.1126/science.1223447]
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