The task of cutting greenhouse gas emissions enough to avert a dangerous rise in global temperatures may be far more difficult than previous research suggested, say scientists who have just published studies indicating that it would require the world to cease carbon emissions altogether within a matter of decades.
Their findings, published in separate journals over the past few weeks, suggest that both industrialized and developing nations must wean themselves off fossil fuels by as early as mid-century in order to prevent warming that could change precipitation patterns and dry up sources of water worldwide.
Using advanced computer models to factor in deep-sea warming and other aspects of the carbon cycle that naturally creates and removes carbon dioxide (CO2), the scientists, from countries including the United States, Canada and Germany, are delivering a simple message: The world must bring carbon emissions down to near zero to keep temperatures from rising further.
"The question is, what if we don't want the Earth to warm anymore?" asked Carnegie Institution senior scientist Ken Caldeira, co-author of a paper published last week in the journal Geophysical Research Letters. "The answer implies a much more radical change to our energy system than people are thinking about."
Although many nations have been pledging steps to curb emissions for nearly a decade, the world's output of carbon from human activities totals about 10 billion tons a year and has been steadily rising.
For now, at least, a goal of zero emissions appears well beyond the reach of politicians here and abroad. U.S. leaders are just beginning to grapple with setting any mandatory limit on greenhouse gases. The Senate is poised to vote in June on legislation that would reduce U.S. emissions by 70 percent by 2050; the two Democratic senators running for president, Hillary Rodham Clinton (N.Y.) and Barack Obama (Ill.), back an 80 percent cut. The Republican presidential nominee, Sen. John McCain (Ariz.), supports a 60 percent reduction by mid-century.