Effect of pollution will last for generations

http://news.independent.co.uk/uk/environment/story.jsp?story=83041

By Steve Connor

12 July 2001

Uncertainties still remain in the scientific assessment of the changes in global climate but scientists are convinced that, whatever happens, the effect of human pollution will be seen for generations.

The area of greatest doubt relates to the accuracy of the computer models used by climate researchers in gauging the effect of pumping out millions of tons of greenhouse gases from factories, cars and homes in the industrial world.

Critics of the idea that global warming is caused by man-made emissions have focused on these computer models, saying the conclusions you get from them merely reflect what assumptions their creators have put in. If you put garbage in, the argument goes, then you get garbage out.

However, scientists from the Intergovernmental Panel on Climatic Change (of the UN) have vigorously defended their modelling techniques in their latest report although they accept that a serious lack of scientific confidence in certain areas, especially in predicting what will happen over the next 100 years and beyond.

One of the most difficult areas is distinguishing between natural variation in climate – an inherently "chaotic" system – and changes resulting from the man-made emissions of greenhouse gases. Computer models have attempted to tease apart the natural "forcing" of the greenhouse effect from man-made, or anthropogenic influences.

A positive "radiative forcing", such as that caused by an increasing concentration of greenhouse gases in the atmosphere, tends to warm the Earth's surface. A negative radiative forcing, caused for instance by the release of particles into the atmosphere from a volcanic explosion, causes cooling.

Computer modellers try to assess the impact of each phenomenon that can influence this balance between warming and cooling, which is why an unexpected event such as a volcanic explosion can blow their assessments off course.

"Confidence in the ability of models to project future climate has increased," the IPCC scientists say, while admitting that such models cannot simulate all aspects of climate. "Nevertheless, confidence in the ability of these models to provide useful projections of future climate has improved due to their demonstrated performance on a range of space and time scales."

The models suggest that the coming century will pose unique problems for society when the impact of global warming begins to bite. "The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years," the scientists say.

One of the greatest unknowns is what will happen to the vital ocean currents, which move tremendous amounts of heat around the planet and keep the British Isles from freezing up in winter. "Beyond 2100, the thermohaline circulation could completely, and possibly irreversibly, shut down in either hemisphere if the change in radiative forcing is large enough and applied long enough," the IPCC scientists suggest.

-- Swissrose (cellier3@mindspring.com), July 12, 2001