`Global warming could reduce rainfall`

British scientists have warned that global warming could reduce rainfall.

Updated: Aug 31, 2010, 18:04 PM IST

London: British scientists have warned that
global warming could reduce rainfall, contrary to the belief
that rising temperatures lead to increase in overall
precipitation levels.

Previous studies have shown that rainfall will increase
globally by 2-3 per cent for every degree Celsius that the
Earth`s surface heats up.

But, scientists at the University of Leeds and the Met
Office Hadley Centre in UK, who looked at a range of climate
change scenarios, found that rainfall may actually decline if
temperature in the atmosphere continues to increase.

"Clearly there`s something else going on," said lead
author of the study Dr Timothy Andrews of Leeds University.
"We found that precipitation isn`t just affected by
temperature change at the surface. It also responds directly
to increased heating in the atmosphere," Dr Andrews was quoted
as saying by PlanetEearth.

And because the atmosphere responds to heating much more
quickly than the surface -- over days rather than decades --
the effect on rainfall is also much faster, he said.

According to the scientists, the various mechanisms that
cause global warming work differently on the atmosphere and
the surface.

Increased solar radiation, greenhouse gases or dark
aerosols -- particles in the air -- all eventually warm the
Earth`s surface. But they act differently on atmospheric
temperature and it`s these effects that can produce an
immediate change in rainfall.

And crucially, this fast atmospheric response seems to
suppress rather than increase rainfall, they said.

Black carbon aerosols, according to the scientists, can
absorb enough sunlight in the atmosphere to suppress the
rainfall response to global warming, and the immediate result
will be less rainfall.

So there are two effects going on in tandem: a fast
atmospheric response that is closely linked with the type of
climate change mechanism, and a slower response to surface
temperature change that happens regardless of the climate
change mechanism.