Cuts in carbon dioxide pollution not enough, 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 man-made carbon dioxide can be added to the air before warming exceeds an increase of 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 today'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.

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 Obama said he wants to cut US 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 coauthor 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.