One of the more perplexing factors of climate is the role of aerosols. Although most people probably associate "aerosols" with things like hair spray, scientists actually use the term to refer to fine particles suspended in the air. These particles are a mix of salts, mineral dust, carbon and other ingredients. Some aerosols come from natural sources, like volcanoes, but most are from human activities, such as burning wood and coal.
These particles are bad for human health and they can also alter the climate. Some of them reflect sunlight back into space - and thus cool the earth to certain extent - while others absorb sunlight, heat the air, and contribute to global warming. It is the latter particles, called «black carbon» or «soot» that have especially interested scientists because many of our dirty energy sources like coal, wood and diesel produce it in large quantities. And scientists say that it may be the biggest single contributor to global warming after carbon dioxide.
We can see soot in the air on smoggy days in our cities - it forms part of the brown haze that covers urban areas. But soot is much worse in many developing countries like China and India, which use far more coal and wood as fuel for industry, heating and cooking. These fuels are inefficient and dirty at the best of times. Using old, wasteful combustion technologies (in many cases simply open cooking fires) makes them even worse. The resulting air pollution in the towns and cities of many developing countries has become a terrible health hazard. Soot is known to cause cancer and is a major cause of illness and death in these areas.
All that soot in the air is also having a significant effect on regional climate. A recent study published in the journal Science reported that soot emissions from China and India may be responsible for increased droughts in northeast China and floods in southeast parts of that country. Northeast China has suffered from increasingly severe dust storms that may be due to a combination of poor land-use practices (such as overgrazing and forest destruction) and the effects of soot on the area’s climate. Soot and other particles in the air are also thought to be blocking sunlight, reducing photosynthesis and lowering crop yields. Last year, a plume of soot and dust from Asian storms actually found its way across the pacific to North America.
If soot is such an important factor in regional climate change, does it mean that we should be going after China and India to reduce their soot emissions, rather than reducing our own greenhouse gas emissions as is required by the Kyoto Protocol? No. It means we should be doing both. But it should be done fairly. Developed and developing nations are not exactly on a level playing field. Telling an auto company that it needs to make more fuel-efficient SUVs and telling a Chinese peasant that her cooking fire needs to produce less soot are not exactly equal on the fairness scale. And unlike greenhouse gases, which build up in the atmosphere and contribute to an overall warming effect for hundreds of years, soot’s effect on climate is more localized and short-term.
So we have to address both problems. The Kyoto Protocol offers us a starting point because mechanisms built into the treaty allow developed counties to fund energy-efficiency projects in the developing world and obtain greenhouse gas "credits" for the emissions reduced. Wise use of such mechanisms could be beneficial to both parties and also start to reduce the substantial health and environmental damage caused by soot.