Soot and pollutants like it are among the last climate change agents to be fully appreciated by science, but their control could lead to the first international victory in the fight against global warming.
These aerosols may feature in a fascinating interplay of science and policy in the lead-up to the United Nations' climate conference in Copenhagen this December, but only if conference participants can broaden their perspective on the causes of global warming.
Today the future is on display in Long Beach, where 300 experts are gathered at the CALSTART Clean Heavy Duty vehicle conference. The showcased buses and bulldozers represent important recent progress in eliminating soot emissions from construction equipment and similar diesel heavy vehicles.
The upside of this innovation is immediate. Small particles, especially those less than 2.5 microns across (known as PM2.5), are especially damaging to respiratory health, since they embed deep in lung tissue. Since the U.S. Environmental Protection Agency introduced abatement standards in 1997, only a handful of American counties, most clustered in the Central Valley, were failing to meet the standard by 2006. This achievement arose from much cleaner diesel burning technology being discussed in Long Beach today and the curbing of smokestack emissions when the acid rain problem was addressed years ago.
But particulate pollution is not a solely homegrown product. Each continent in the Northern Hemisphere airmails a “gift” of aerosols from its northeastern tip, a gift destined for the western side of its transoceanic partner. As China dirties snow in the Sierra Nevada, North America is helping make the white cliffs of Dover a tad more beige. Luckily the gift doesn't linger in the atmosphere. Even fine solid particles tend to fall out – or get washed out – of the atmosphere in 10 to 14 days. Once we figure out how to stop making such soot, its bad effects mostly disappear.
Unfortunately some continents still produce massive quantities of carbon soot from industrial processes and the collective belch of household stoves running on what fuels are locally available – usually wood and dung. Recently my colleague at Scripps, Veerabhadran Ramanathan, has documented the impact of so-called “brown clouds” on the melt of Himalayan glaciers and disruption of monsoon patterns. Starting in 1958, geochemist Dave Keeling established that human greenhouse gases, chiefly carbon dioxide, are responsible for most of the excess heat trapped by the atmosphere and fed into global oceans. Methane and ozone-depleting CFCs are the next in line. But Ramanathan has estimated that certain aerosols such as carbon soot also play a significant role, perhaps as much as 10 to 15 percent of the total excess heating.
So here is a perfect “low hanging fruit” in the fight against global warming – worldwide reduction of a certifiable health hazard that has already been mostly reduced in Europe and North America with readily available, proven, and cheap technology. The problem at the moment is that state and national emissions regulations, such as California's AB 32, and even international agreements such as the Kyoto protocol, only address greenhouse gases (which can survive for hundreds of years in the atmosphere) and not aerosols like carbon soot, which also trap heat. So the race is on for all countries, developed and developing, not only to reach a deal on greenhouse gases, but also to include all human-made heat-trapping actors in the drama, and that would include carbon soot. Copenhagen happens in December, and nine months is an awfully short time in international diplomacy.
Curbing carbon soot pollution in no way solves global warming completely. But it does establish an early win and buys us some time. Even modest benefits and the improvement of health worldwide make it a worthy short-term priority, one that will eventually lead to the main event, the reduction of carbon dioxide in the atmosphere to sustainable levels.
Haymet is director of Scripps Institution of Oceanography at the University of California San Diego.