It’s worse than we thought – According to the study recently published in the Journal of Geophysical Research: Atmospheres, black carbon ranks as the second-largest human contributor to climate change, exerting twice as much impact as previously believed. Sarah Doherty, a research scientist with the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) at the University of Washington, is one of four lead authors on the four-year assessment done by an international panel of scientists. Black carbon (also known as soot) has a complex role in the climate. Dark particles in the air work to shade the Earth’s surface while warming the atmosphere. Soot that settles on snow and ice darkens the surface to absorb more sunlight and increase melting. Its particles also influence cloud formation in ways that can have either a cooling or warming impact.
Background: In 2009, Doherty and a team of 31 international scientists set out to make careful estimates of all black carbon sources using data from monitoring stations around the world. According to the analysis, soot is second only to carbon dioxide in the amount of heat it traps in the atmosphere. The new estimate of black carbon’s heat-trapping power is about twice that made by the Intergovernmental Panel on Climate Change in 2007.
Significance: If black carbon is responsible for trapping so much heat, then reducing soot may be an effective way to slow down the planet’s warming. Black carbon washes out of the atmosphere quickly so reducing soot emissions would lead to a fast fall in the concentration of black carbon (carbon dioxide, by contrast, lingers in the atmosphere for centuries). While soot’s haze can block sunlight and cool the atmosphere, the report found that some sources - especially the burning of coal and diesel fuel - produce a lot of warming with very little compensation cooling, so researchers suggest that reducing these sources should be the top priority in efforts to fight global warming. This work supports NOAA’s goal to improve understanding of the changing climate system and its impacts.
Contact: Sarah Doherty, JISAO Research Scientist