January 27, 2009

Climate Damage Already Irreversible, Study Declares

Researchers declared Monday that many damaging effects of climate change are already basically irreversible, warning that even if carbon emissions can somehow be halted temperatures around the globe will remain high until at least the year 3000.

"People have imagined that if we stopped emitting carbon dioxide the climate would go back to normal in 100 years, 200 years; that's not true," climate researcher Susan Solomon said in a teleconference.

Solomon, a senior NOAA scientist, also said that the study showed that current human choices on carbon dioxide emissions are set to "irreversibly change the planet," and that would remain for 1,000 years, even if humans stopped adding carbon to the atmosphere immediately.

President Barack Obama ordered reviews that could lead to greater fuel efficiency and cleaner air, saying the Earth's future depends on cutting air pollution.

According to Solomon, "Climate change is low, but it is unstoppable," all the more reason to act quickly, so the long-term situation does not get even worse.

"It's not like air pollution where if we turn off a smokestack, in a few days the air is clear," said Alan Robock, of the Center for Environmental Prediction at Rutgers University. "It means we have to try even harder to reduce emissions," he said in a telephone interview.

Solomon's report "is quite important, not alarmist, and very important for the current debates on climate policy," added Jonathan Overpeck, a climate researcher at the University of Arizona.

Solomon noted in her paper that temperatures around the globe have risen and changes in rainfall patterns have been observed in areas around the Mediterranean, southern Africa and southwestern North America.

The researchers said that the warmer climate also is causing expansion of the ocean, and that it is expected to increase with the melting of ice on Greenland and Antarctica.

"I don't think that the very long time scale of the persistence of these effects has been understood," Solomon said.

Solomon said, that because water absorbs a lot of energy to warm up, that global warming has been slowed by the ocean.  However, that good effect will not wane over time, the ocean will help keep the planet warmer by giving off its accumulated heat to the air.

The "greenhouse effect" is when gases in the atmosphere trap heat from solar radiation and raise the planet's temperature.  Carbon dioxide has been the most important of those gases because it remains in the air for hundreds of years.  Other gases are responsible as well for nearly half of the warming, they degrade more rapidly, Solomon said.

The industrial revolution of the air use to contain about 280 parts per million of carbon dioxide.  Today it is up 385 ppm, and politicians and scientists have debated at what level is could be stabilized.

Solomon's paper concludes that if CO2 is allowed to peak at 450-600 parts per million, the results would include persistent decreases in dry-season rainfall that are comparable to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.

A senior scientist at the National Center for Atmospheric Research, Gerald Meehl, said, "The real concern is that the longer we wait to do something, the higher the level of irreversible climate change to which we'll have to adapt." Meehl was not part of Solomon's research team.

Head of climate analysis at the center, Kevin Trenberth, said, while scientists have been aware of the long-term aspects of climate change, the new report highlights and provides more specifics on them.

"This aspect is one that is poorly appreciated by policy-makers and the general public and it is real," said Trenberth, who was not part of the research group.

"The temperature changes and the sea level changes are, if anything underestimated and quite conservative, especially for sea level," he said.

He did agree that the rainfall changes mentioned in the paper are under way, Trenberth disagreed with some details of that part of the report.

"Even so, there would be changes in snow (to rain), snow pack and water resources, and irreversible consequences even if not quite the way the authors describe," he said. "The policy relevance is clear: We need to act sooner ... 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. In fact, as the authors point out, it is already too late for some effects."

Co-authors of the paper were Gian-Kaspar Plattner and Reto Knutti of the Swiss Federal Institute of Technology in Zurich and Pierre Friedlingstein of the National Institute for Scientific Research, Gif sur Yvette, France.

The Office of Science at the Department of Energy supported the research.


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