Climate change: Artificial worlds hold key to figuring out a real problem
Pastor Dale Morgan
Climate change: Artificial worlds hold key to figuring out a real problem*
PARIS, Jan 24 (AFP) Jan 24, 2007
Small, brown-haired and soft-voiced, Pascale Braconnot cuts an unlikely
figure as Master of Planet Earth.
But with a few deft movements of her fingers, Braconnot can conjure up
our planet and spin it until the end of the century.
At her command, oceans rise. Tropical Africa becomes stricken by
drought. Rainstorms sweep South Asia, the Arctic icecap shrivels and bit
by bit, Amazonia tragically becomes savannah.
Braconnot is head of computer modelling at the Laboratory for Climate
and Environment Sciences (LSCE) near Paris, run by France's top
scientific agencies to get a fix on where Earth's troubled climate
system is headed.
Climate models are simulations of the global weather system, run on
number-crunching supercomputers.
Less than a decade ago, these programmes were acknowledged by their own
creators as being flawed by lack of computing power and poor data about
the complex ballet between oceans, land, atmosphere, ice, greenhouse
gases and solar radiation.
Today, though, the best climate models are able to recreate Earth's
climate in the past, and forecast with confidence the global temperature
and rise in mean sea levels by 2100 depending on future levels of carbon
pollution in the air.
They can also make some prediction, albeit less accurately, about
regional impacts -- which areas of the world will be most hit by a
changed climate and which areas may potentially benefit.
These models provide the backbone of a long-awaited report by the UN's
top panel of climate experts, due to be issued in Paris on February 2.
What has happened between then and now?
One big change has been a rush of robust data about Earth's climate in
the past.
This has come from sources as diverse as carbon dioxide (CO2) in
600,000-year-old Antarctic ice cores; from ancient tree stumps preserved
in peat bogs; and from coral, whose growth rates are influenced by
temperature and water salinity.
These have guided scientists about the climate of the distant past,
helping them to factor out natural variations in the warming scenario
and confirming that man-made greenhouse gases are to blame for today's
scary temperature rise.
Added to that are data from newly-launched Earth-monitoring satellites,
oceanographic buoys and improved meteorological surveillance in poor
countries, adding many pixels to the snapshot of the climate today.
Despite these strides, climate science is still a new discipline, and
every year experts uncover new complexities or uncertainties.
"One of them is cloud cover," says Braconnot, explaining that the type
of cloud and its altitude either cool the surface below -- or conversely
trap solar heat instead of letting it escape into space.
"We have had to implement a number of simplifications, even
oversimplifications about clouds in our model."
Another area of doubt is aerosols -- dust, such as industrial
particulates, that is thrown high into the atmosphere and which reflects
solar rays (thus having a cooling effect) but which also serves as a
seed for raindrops, thus shifting patterns of precipitation.
Pascale Delecluse, deputy director of research at Meteo France, says
models are also crimped by a newly-discovered phenomenon called
"positive feedbacks."
These, in essence, are vicious circles. For instance, warming will thaw
the permafrost in northern latitudes, releasing methane that had been
stored for millennia in the frozen soil. The methane, a potent
greenhouse gas, thus stokes the warming.
Other likely feedbacks include saturation of the oceans, whose plankton
also absorb CO2, and loss of snow and ice cover in high latitudes and
altitudes (snow and ice reflect the Sun, so when they disappear, the
uncovered ground warms quickly, thus melting more snow on neighbouring
ground).
"Most scenarios work with the state of the Earth as we know it today.
Models are still incapable of factoring in the effects of feedbacks,"
admits Delecluse.
The Intergovernmental Panel on Climate Change (IPCC), the UN's paramount
scientific authority on the causes and effects of global warming, will
issue a much-awaited report next week.