Scientists know that dust affects climate. Tiny particles create veils that reflect sunlight and cool the atmosphere. Dark particles absorb sunshine and warm things up. But as scientists look deeper into the dust-climate connection, they find that they have underestimated its importance.
Research published April 3 in Nature reveals the tight linkage between atmospheric dust flows and Antarctic temperatures during ice ages over the past 800,000 years. A research review published March 23 in Nature Geoscience online shows that black carbon particles in the atmosphere have a more powerful global-warming effect than any of the greenhouse gases except carbon dioxide. And these particles are 60 percent as effective as CO2 itself. That's far more powerful than the estimate in last year's report of the UN-sponsored Intergovernmental Panel on Climate Change (IPCC).
The good news is that black carbon particles such as diesel soot or wood-stove smoke only stay airborne for weeks. (It takes a century to get rid of today's CO2 emissions.) This fact offers an opportunity for instant payback, say study authors V. Ramanathan at Scripps Institution of Oceanography in San Diego and Gregory Carmichael at the University of Iowa in Iowa City. In an announcement from Scripps, the authors note that commercially available technologies exist to cut back soot emissions substantially. Using them would rapidly reduce black-carbon warming.
Dr. Ramanathan explains that the difference between the study estimate of the sooty warming and that of the IPCC is the difference between inadequate computer modeling and actual observation. The Carmichael-Ramanathan estimate integrated data from satellite, aircraft, and ground instrumentation. This shows a black-particle warming of 0.9 watts per square meter. The IPCC estimate was between 0.2 and 0.4 watts per square meter.
In China and India, home cooking with wood and cow dung in addition to home heating with coal contribute 25 to 35 percent of the global atmosphere's black particle burden. Areas that use a lot of diesel fuel contribute comparable amounts. Ramanathan says the next phase of this research is "to examine if black carbon is also having a large role in the retreat of arctic sea ice and Himalayan glaciers."
Meanwhile, Fabrice Lambert at the University of Bern in Switzerland and colleagues are taking advantage of an unbroken 800,000-year climate record in an Antarctic ice core to track dust flows into the region. They find what they call "a significant correlation" between dust coming into the region and Antarctic cooling. They suggest that the 25-fold increase in dust inflow they see during glacial times relates to stronger South American dust sources. Also, less rainfall during those times allows dust to stay airborne longer than when more abundant rain washed it out. It's what the research team calls "a progressive coupling of the climates of Antarctic and lower latitudes" during glacial times.
Such results show that climate modelers need to take careful account of dust in their climate change scenarios. So, too, should the delegates from 163 countries now meeting in Bangkok, Thailand, as they schedule the drafting of a new global-warming mitigation agreement. They might find the prospect of a quick payback from curbing black-particle emissions attractive.