Researchers at the National Center for Atmospheric Research in Boulder, Colorado, used a computer model to predict probable long-term increases in the Earth's temperature if no actions are taken to curb the emissions of gases and pollutants that many scientists blame for global warming.

Members of a US Greenpeace delegation protest against the role of the United States at the international climate protection conference in Bonn, July 19, 2001. Environment ministers fought to salvage the Kyoto accord despite the unbending position of the United States, the world's biggest polluter, to the 1997 pact against global warming. (Michael Dalder/Reuters)

The researchers said the planet has warmed up by about 1 degrees over the last century. But they say it is likely to heat up by about 1 or 2 degrees as early as 2030.

By 2100, the most likely increase would be in the range of 4 to 7 degrees, while there is a 90 percent chance global average temperatures will rise 3 to 9 degrees, they said.

Tom Wigley, the lead researcher, said a broad range of possible long-term temperature changes does little to assist policy makers. For example, an estimated global warming range of 2.5 to 10.4 degrees was announced this year by the Intergovernmental Panel on Climate Change (IPCC), established in 1988 by the U.N. World Meteorological Organization and U.N. Environment Program.

Wigley said the new study aimed to tell policy makers what level of global warming is most likely.

World leaders have been at loggerheads over what steps governments need to take to reduce emissions -- especially after the United States withdrew in March from the 1997 Kyoto Protocol, a global deal to cut pollution.

UNCERTAINTIES WEIGHED

He said the computer model sought to account for various uncertainties that could impact warming.

``There are two that absolutely dominate,'' Wigley, whose study appears in the journal Science, said in an interview.

``One is human beings, and uncertainties in things like population and economic growth and technological development and awareness of environmental issues. Those human and socioeconomic uncertainties essentially produce a very wide range of possible emissions for the gases that might cause changes in climate in the future,'' he added.

The other primary uncertainty factor, Wigley added, is just how sensitive the Earth's climate system is to man-made influences.

Some critics say there is scant evidence of a man-made cause of global warming.

New estimates of sulfur dioxide and other emissions, along with updated information on carbon storage, ocean circulation, radiation, and other components of the Earth system have improved computer climate models, the researchers said.

Even aggressive action to curb so-called greenhouse emissions and other factors that may contribute to global warming may be too late prevent continued temperature rises, Wigley said.

``The climate system is like a giant flywheel. Even if we do a lot of things in the near future to try to reduce emissions or reduce the growth of emissions, then the system has a lot of inertia and it is going to keep warming for a long, long time,'' Wigley said.

``So already in place are a lot of unavoidable climate change consequences no matter what we do. But that doesn't mean we should give up. And there are a lot of things we can do. And what we have to do is balance the economic cost against the environmental cost.''

In a commentary in Science, experts at the Massachusetts Institute of Technology and the University of North Carolina note the difficulty in making such temperature predictions.

``Future emissions of greenhouse gases, their climatic effects and the resulting environmental and economic consequences are subject to large uncertainties,'' said the experts, led by MIT's John Reilly.

Many scientists believe emissions of certain pollutants from industry, power plants, vehicles and other sources threaten to disrupt global climate and ecosystems by causing the Earth's atmosphere to trap more of the sun's energy, triggering global warming.

Copyright © 2001 Reuters Limited.

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