Black carbon’s contribution to climate change underestimated

carbon influences climate in many ways, both directly and indirectly, and all of these effects must be considered jointly”, says co-lead author Sarah Doherty of the University of Washington, an expert in snow measurements. The dark particles absorb incoming and scattered heat from the sun (solar radiation); they can promote the formation of clouds that can have either cooling or warming impact; and black carbon can fall on the surface of snow and ice, promoting warming and increasing melting.  In addition, many sources of black carbon also emit other particles whose effects counteract black carbon, providing a cooling effect.

The research team quantified all the complexities of black carbon and the impacts of co-emitted pollutants for different sources, taking into account uncertainties in measurements and calculations. The study suggests mitigation of black carbon emissions for climate benefits must consider all emissions from each source and their complex influences on climate.  Based on the analysis, black carbon emission reductions targeting diesel engines followed by some types of wood and coal burning in small household burners would have an immediate cooling impact.

In addition, the report finds black carbon is a significant cause of the rapid warming in the Northern Hemisphere at mid to high latitudes, including the northern United States, Canada, northern Europe and northern Asia. Its impacts can also be felt farther south, inducing changes in rainfall patterns from the Asian Monsoon.  This demonstrates that curbing black carbon emissions could have significant impact on reducing regional climate change while having a positive impact on human health. 

“Policy makers, like the Climate and Clean Air Coalition, are talking about ways to slow global warming by reducing black carbon emissions. This study shows that this is a viable option for some black carbon sources and since black carbon is short lived, the impacts would be noticed immediately.  Mitigating black carbon is good for curbing short-term climate change, but to really solve the long-term climate problem, carbon dioxide emissions must also be reduced,” says co-lead author Tami Bond from the University of Illinois at Urbana-Champaign.

The release notes that the International Global Atmospheric Chemistry (IGAC) Project was formed in 1990 to address growing international concern over rapid changes observed in the Earth’s atmosphere. IGAC operates under the umbrella of the International Geosphere-Biosphere Program (IGBP) and is jointly sponsored by the international Commission on Atmospheric Chemistry and Global Pollution (iCACGP).  IGAC’s mission is to coordinate and foster atmospheric chemistry research toward a sustainable world. The IGAC International Project Office is hosted by the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado.

— Read more in S. Sharma et al., “16-year simulation of Arctic black carbon: transport, source contribution, and sensitivity analysis on deposition,” Journal of Geophysical Research: Atmospheres (19 January 2013) (DOI: 10.1029/2012JD017774); and T. C. Bond et al., “Bounding the role of black carbon in the climate system: A scientific assessment,” Journal of Geophysical Research: Atmospheres (forthcoming) (DOI: 10.1002/jgrd.50171)