What harm man can do, nature can undo -- at least for a while. While the alumni of the Rio environment conference undertake complex schemes to combat global warming, scientists are finding that Mother Nature is quietly applying her own highly efficient methods.
Since the Industrial Revolution, gases like carbon dioxide and methane have been wafting into the atmosphere, where they let the sun's rays in to warm the earth but keep excess heat from escaping back into space. Acting like the glass walls of a greenhouse, these gases have forced the planet's temperature up 0.8 degreesC (1.5 degreesF) over the past century or so. If the trend continues, temperatures could increase up to 5 degreesC (9 degreesF) within 50 years, raising the sea level, distorting weather patterns and causing widespread environmental disruption.
But now the ecological disaster known as global warming has been put off five years at least, thanks to last year's eruption of Mount Pinatubo. When the Philippine volcano blew its top, it lofted some 20 million tons of sulfur dioxide into the upper atmosphere. Since then, the stuff has circled the globe, forming a layer of droplets floating in the stratosphere, between 19 and 23 km (12 and 14 miles) above the surface. Scientists predicted that the droplets would act as a worldwide sun shield. Satellite measurements are proving they were right: the planet has cooled off about 0.5 degreesC (1 degreesF) since Pinatubo, erasing nearly a century's worth of rising temperatures. Unfortunately, the fallout will disappear in three to five years. After that, global warming should resume, as menacingly as ever.