Soot – The Forgotten Greenhouse Aerosol

While most key players have been focusing on reducing carbon dioxide and other greenhouse gasses, soot emissions have largely been forgotten. This may have to change if we are to meet the strict targets set by the EU and especially to combat the more rapid warming seen in the Polar regions, according to discussion at the 242nd National Meeting & Exposition of the American Chemical Society (ACS).

The Polar region is particularly important in the battle against climate change as it is an area of crucial feedback effects. As the ice caps melt, the white reflective ice is replaced by the dark absorbent ocean, warming the region and increasing melt. Some even suggest that it could prove to be a crucial tipping point, where a point of no return could be reached.

Soot is an aerosol; light coloured aerosols like sea salt have a net cooling effect on the atmosphere, while darker colours like soot have a net warming effect. Major sources of soot include exhaust from diesel vehicles, ships, aircraft, agricultural machines, construction equipment and the wood fires of people in developing countries. Soot in the atmosphere is dark and therefore absorbs heat faster than other particles, which it then radiates, warming the surrounding atmosphere. It also acts as a net, trapping heat that is leaving the Earth. It is estimated to account for 17% of global warming currently.

Another reason to focus on soot is that the effects of removing it are immediate. Carbon dioxide takes generations to leave the atmosphere, but soot stays there for a matter of days, making a clamp down on soot emissions an excellent way to reduce global warming. Mark Jacobson, Ph.D., of Stanford University believes we could cut soot emissions by 90% in the next decade. This effective removal of soot from the equation would have a net 3 degree reduction in temperatures in the Arctic, according to Jacobson.

Soot is relatively easily removed too; particulate filters on vehicles and a drive to introduce clean burning stoves in the developing world would deal with a great deal of the problem.

It is unfortunate that previous climate models have not looked at the effect of soot, as it is now not considered to be a key goal by the IPCC. This will hopefully change over the coming years. While measures to reduce Carbon Dioxide are of course key, reducing particulates like soot could prove to be a crucial short term measure to avoid rapid climate change.