The God Species_ How the Planet Can Survive the Age of Humans - Mark Lynas [100]
What is certain, however, is that aerosols all have a very short lifetime. Unlike carbon dioxide, which stays in the atmosphere for decades or even centuries, dust, smoke, and sulfur particles are washed away by rain in a matter of days. So while the greenhouse gas burden now changing the climate results from accumulated carbon emissions over more than two hundred years, aerosols circulating in the air were released at most only a week or two ago. This is a problem that only persists as long as we go on causing it. Consequently, it will be one of the easiest planetary boundaries to address. Although the planetary boundaries expert group—as a result of the tremendous uncertainties attached to aerosol pollution’s impacts on the climate and Earth system in general—has been unable to come up with a specific quantified limit to atmospheric concentrations of any specific pollutants, this hardly matters. It is clear that having clean air will produce a lot more benefits than drawbacks. Moreover, we can clean up our activities relatively quickly and cheaply, with readily available technology. Additionally, this is a problem that will solve itself as developing countries become more prosperous and their populations demand pollution reductions. The challenge is to solve the problem in a way that complements, rather than conflicts with, the other more challenging planetary boundaries.
FIRE, FLOOD, AND ICE
Perhaps the most famous pall of pollution anywhere in the world sits over India. The so-called Asian Brown Cloud is the combined product of thousands of coal-burning power stations, tens of thousands of factories and millions of open fires burning biomass like wood and dung, and is now a semipermanent feature of the South Asian meteorological map. By reducing solar radiation at the surface, it has cooled the entire north Indian Ocean and changed the dynamics of the monsoon, perhaps the world’s most spectacular and important meteorological phenomenon. At its height in the spring, the brown cloud creeps north up to the ramparts of the high Nepali Himalaya, its sooty deposits darkening the snow on the flanks of Mount Everest itself.
If China is included too, rapidly industrializing Asia is the densest source of global pollutants. Scientists at high-altitude monitoring sites on Mauna Loa volcano in Hawaii, and in Boulder, Colorado, in the Rockies, puzzled at first by the rising levels of sulfur their laser measurements found in the stratosphere, have discovered that Chinese coal-fired power stations are now a leading source of sulfur reaching the high stratosphere.2 If Chinese sulfur emissions double over the next couple of decades as predicted, they will be equivalent to 5 percent of the 1991 Pinatubo eruption—the second largest volcanic explosion of the entire twentieth century. This will, experts calculate, reduce temperatures in the lower atmosphere by 0.03°C and will even affect the ozone layer—truly a worldwide impact. Aerosol pollutants from India are hoisted 15 vertical kilometers by powerful updrafts during the country’s violent monsoon rainstorms, allowing them too to circumnavigate the globe.3
Those who suffer most from the direct impacts of this pollution, of course, are those living in Asia. Airborne particulates are a leading cause of heart and lung disease throughout the continent, where three billion people breathe air classed as dangerous by the World Health Organization.4 The Chinese Academy for Environmental Planning blames air pollution for 411,000 premature deaths each year across the country, probably a serious underestimate given the year-round smog pall hanging over most Chinese cities. In Beijing, where