Even if by some miracle of environmental activism global carbon dioxide levels reverted to pre-industrial levels, it still would take 1,000 years or longer for the climate changes already triggered to be reversed, scientists said Monday.
The gas that is already there and the heat that has been absorbed by the ocean will exert their effects for centuries, according to the analysis, published Monday in the Proceedings of the National Academy of Science.
Over the long haul, the warming will melt the polar icecaps more than previously had been estimated, raising ocean levels substantially, the report said.
And changes in rainfall patterns will bring droughts comparable to those that caused the 1930s Dust Bowl to the American Southwest, southern Europe, northern Africa and western Australia.
“People have imagined that if we stopped emitting carbon dioxide, the climate would go back to normal in 100 years, 200 years,” lead author Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration, said in a telephone news conference. “That’s not true.”
The changes will persist until at least the year 3000, said Solomon, who conducted the study with colleagues in Switzerland and France.
Scientists familiar with the report said it emphasizes the need for immediate action to control emissions.
“As a climate scientist, this was my intuition,” said geoscientist Jonathan T. Overpeck of the University of Arizona. “But they have done a really good job of working through the details and … make a case that the situation is more dire than we thought if we don’t act quickly and aggressively to curb carbon dioxide emissions.”
Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in Boulder, Colo., said that the persistence of climate change caused by global warming “is poorly appreciated by policymakers and the general public and it is real.
“The policy relevance is clear: We need to act sooner, even if there is some doubt about exactly what will happen, because by the time the public and policy makers really realize the changes are here, it is far too late to do anything about it,” he added.
The new finding depends upon the fact that water in the ocean circulates very slowly. The primary way carbon dioxide is removed from the atmosphere is through absorption in the ocean, and that is an incredibly slow process because it takes a long time for surface waters saturated with the gas to be replaced by deeper waters that can absorb more.
Carbon dioxide accounts for only about half of the global warming caused by greenhouse gases, but the other gases are removed from the atmosphere much more quickly. Thus, the long-term effects of carbon dioxide will have the greatest influence on climate change, according to the findings.
Moreover, heat absorbed by the ocean is released very slowly, contributing to global warming even if the concentration of greenhouse gases should decline, the authors said.
Solomon said in a statement that absorption of carbon dioxide by the oceans and release of heat from the oceans – the one process acting to cool the earth and the other to warm it – will “work against each other to keep temperatures almost constant for more than 1,000 years.”
Said geoscientist Jorge L. Sarmiento of Princeton University, “This is really a wake-up call about the seriousness of this issue.”
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