CO2 Must Be Slashed More to Limit Warming

April 29, 2009 -- If the world is going to limit global warming to just a few degrees, it has to slash carbon dioxide pollution much more than now being discussed, two new science studies say.

Carbon dioxide from the burning of fossil fuels -- coal, oil and natural gas -- is the chief cause of global warming.

The studies found there's a limit to how much manmade carbon dioxide can be added to the air before warming exceeds an increase of 2 degrees Celsius or 3.6 degrees Fahrenheit -- the level that many governments have set as a goal. World average temperatures going higher than that may be dangerous, some scientists say.

To keep under that danger level, the world has to spew less than 1.1 trillion tons of carbon dioxide in the first half of the 21st Century, according to studies published in Thursday's edition of the journal Nature.

In the first nine years of the century, the world has already emitted one-third of that amount and is on pace to hit that trillion ton limit in just 20 years, said climate researcher Malte Meinshausen of Germany's Potsdam Institute for Climate Impact Research and lead author of one of the studies.

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Even if the world ducks under that emissions limit, there is still a 25 percent chance of temperatures exceeding the dangerous mark, he said.

President Barack Obama said he wants to cut U.S. emissions of carbon dioxide by 80 percent. That is a "good start but it's not enough to limit warming," said Bill Hare, a study co-author who is also at the Potsdam Institute.

Assuming that other countries cut their per-person emission levels to match the United States, the United States has to cut its overall pollution by 90 to 95 percent to keep the world from exceeding the 1.1 trillion ton mark, Hare said.

Cutting emissions means not burning as much fossil fuels, leaving about three quarters of the known reserves in the ground, the study authors said.

"Not much at all of coal reserves can be burnt and still keep below" the 3.6 degrees of warming, Hare said.