'Pollutants keeping global warming at bay'
(China Daily/The Guardian)
Updated: 2005-12-23 06:15
Cutting air pollution could trigger a greater surge in global warming than
previously thought, suggesting future rises in sea level and other environmental
consequences have been underestimated, climate scientists reported yesterday.
The warning comes after researchers investigated the effect of fine particles
known as aerosols on climate change. Aerosols particles smaller than
one-hundredth of a millimetre are churned out from factory chimneys, from the
burning of fossil fuels and forest fires, although sea salt and dust particles
swept up by desert storms add to levels detected in the atmosphere.
Because the particles are so light, they remain aloft for long periods, where
they cool the Earth by reflecting radiation from the sun back out to space.
Higher levels of aerosols lead to the formation of brighter clouds made up of
smaller water droplets, which reflect still more of the sun's warming radiation.
Cutting down on aerosols by improving air quality means that the Earth will
in future be less shielded against the sun's rays.
Writing in the journal Nature, scientists at the Meteorological Office and
the US Government's National Oceanic and Atmospheric Administration report that
climate models used to predict future global warming have badly underestimated
the cooling effect of aerosols.
"We found that aerosols actually have twice the cooling effect we thought,"
said Nicolas Bellouin, a climate modeller at the Met Office. The consequence is
that as air quality improves and aerosol levels drop, future warming may be
greater than we currently think."
Bellouin's study suggests that even by conservative estimates, climate models
have got the impact of aerosols on the climate wildly wrong. "The discrepancy
between the models and our observations is not good news," he said.
The scientists used images from a US satellite called Modis to look at how
much sunlight aerosols in the atmosphere reflect back to space on cloud-free
days. Using another satellite called Toms, they were able to separate readings
for the effect of smaller aerosols produced by natural processes from those
produced by human activity.
Scientists had assumed that the amount of sunlight reflected by aerosols from
industry and fuel burning was tiny compared to the extra reflective cloud cover
they caused, but Bellouin's research suggests the processes are equally
important. Bellouin says climate scientists will have to plug the new
information into their models before they can be sure of the implications for
One possibility is that while the latest study shows scientists have
underestimated the so-called direct effect of aerosols reflecting the sun's
rays, they may have overestimated the indirect effect they have on cloud cover,
meaning the overall error of climate models would not be serious.
Earlier this year, Peter Cox at the Centre for Ecology and Hydrology in
Winfrith, Dorset, warned that if the cooling effect of aerosols turned out to be
greater, it could trigger faster global warming.
"It's quite a bizarre thing, because the last thing you want to suggest to
people is that it would be a good idea to have dirty air, but as far as climate
change is concerned, that's right. Everyone would be getting asthma, but the
environment would be cooler.
"That said, the direct effects of air quality, particularly in urban areas,
are so important to human health, that it would be crazy to think of anything
other than health damage," he said.
(China Daily 12/23/2005 page1)