Prior posts have noted the adverse health impacts from small particles, often referred to generally as PM10 and/or PM2.5. Prior posts have also noted the adverse impact of soot on global warming, which because it is black and absorbs heat warms up the atmosphere and whatever it is coating (e.g., glaciers). Yet addressing this problem can both improve public health and decrease global warming.
To date, strategies to address global warming have focused on gases that stay in the atmosphere from medium- to long-term (e.g., methane [half life, 7 years] and carbon dioxide [half life, 19 to 49 years, without getting into the complexities of the CO2 cycling between atmosphere, ocean, plants etc., which could drive the half-life to a 5-100 year "bracket"]). [Regarding impacts of methane, see http://epa.gov/climatechange/ghgemissions/gases/ch4.html. Regarding impacts of CO2, see http://epa.gov/climatechange/ghgemissions/gases/co2.html.]
In contrast, soot stays in the atmosphere for a much shorter period of time. A recent study suggests a serious re-think may be needed because soot is the second most damaging greehouse agent after CO2 and twice as bad as previously believed.
The study found that the soot that is currently present has a warming effect of 1.1 watts per square meter of the Earth's surface. This is greater than methane (a greenhouse gas that I have noted in prior posts is often ignored or downplayed in the discussion of strategy to address global warming) and second only to CO2 at 1.7 watts per square meter. The prior UNEP estimate for soot was 0.3-0.6.
The study argues that the warming from soot will be especially significant in the Northern latitudes (e.g., glaciers, snowpacks). Also, it sees a potential threat to regional precipitation patterns, such as the Asian monsoons. Now, let's turn to the other side of soot. The UNEP attributes 2.4 million deaths per year due to the adverse effect of such particulates on lungs, an issue noted in numerous prior posts. [See http://www.unep.org/ccac/ShortLivedClimatePollutants/tabid/101650/Default.aspx.]
As noted, CO2 lasts a long time in the atmosphere. In contrast, soot drops out within weeks. Controlling soot means that it goes away relatively quickly. In Europe and America, 70% of soot comes fro diesel engines, which may be the more harmful form of such airborne particulates (see http://www.ncbi.nlm.nih.gov/pubmed/21810552). Better exhaust controls and the scrapping of old, high pollution cars would have a major beneficial effect. In the LDC's, the problem also includes inefficient stoves and dirty fuel; these are problems that should be easy to address if well understood and simple technologies are provided to replace the current processes.
The benefits of reducing soot is that it has immediate, local health benefits and is cheaper than addressing CO2 emissions. No global treaty is needed, and there are no free rides; benefits are local with improved health. Such controls may reduce by half a degree the temperature rise projected for global warming, buying politicans and world leaders roughly two additional decades to address controls on methane and CO2.
The study can be found at: http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50171/abstract.