April 17, 2011

Climate change from black carbon depends on altitude

Palo Alto, CA—Scientists have known for decades that black carbon aerosols add to global warming. These airborne particles made of sooty carbon are believed to be among the largest man-made contributors to global warming because they absorb solar radiation and heat the atmosphere. New research from Carnegie's Long Cao and Ken Caldeira, along with colleagues George Ban-Weiss and Govindasamy Bala, quantifies how black carbon's impact on climate depends on its altitude in the atmosphere. Their work, published online by the journal Climate Dynamics, could have important implications for combating global climate change.
Black carbon is emitted from diesel engines and burning wood, among other sources. In the atmosphere, it acts as an absorbing aerosol—a particle that absorbs the sun's heating rays. (Other types of aerosols reflect the sunlight back out into space, providing a cooling effect.) The climate effect of black carbon is difficult to quantify because these particles heat the air around them, affecting clouds even before they begin to heat the land and ocean surface.