NEW SCIENTIST - Smoke is clouding our view of global warming, protecting
the planet from perhaps three-quarters of the greenhouse effect. That
might sound like good news, but experts say that as the cover diminishes
in coming decades, we are in for a dramatic escalation of warming that
could be two or even three times as great as official best guesses. This
was the dramatic conclusion reached last week at a workshop in Dahlem,
Berlin, where top atmospheric scientists got together, including Nobel
laureate Paul Crutzen and Swedish meteorologist Bert Bolin, former
chairman of the UN's Intergovernmental Panel on Climate Change. IPCC
scientists have suspected for a decade that aerosols of smoke and other
particles from burning rainforest, crop waste and fossil fuels are
blocking sunlight and counteracting the warming effect of carbon dioxide
emissions. Until now, they reckoned that aerosols reduced greenhouse
warming by perhaps a quarter, cutting increases by 0.2 °C. So the 0.6 °C
of warming over the past century would have been 0.8 °C without
aerosols.
But the Berlin workshop concluded that the real figure is even higher -
aerosols may have reduced global warming by as much as three-quarters,
cutting increases by 1.8 °C. If so, the good news is that aerosols have
prevented the world getting almost two degrees warmer than it is now.
But the bad news is that the climate system is much more sensitive to
greenhouse gases than previously guessed. As those gases are expected
to continue accumulating in the atmosphere while aerosols stabilise or
fall, that means "dramatic consequences for estimates of future climate
change", the scientists agreed in a draft report from the workshop.