14,000 TIMES FASTER THAN NATURE
Zeebe analyzed carbon dioxide that had been captured in Antarctic ice, and by figuring out how much carbon dioxide was in the atmosphere at various points in time, he and his co-author determined that it waxed and waned along with the world's temperature.
"When the carbon dioxide was low, the temperature was low, and we had an ice age," he said. And while Earth's temperature fell during ice ages and rose during so-called interglacial periods between them, the planet's mean temperature has been going slowly down for about 600,000 years.
The average change in the amount of atmospheric carbon dioxide over the last 600,000 years has been just 22 parts per million by volume, Zeebe said, which means that 22 molecules of carbon dioxide were added to, or removed from, every million molecules of air.
Since the Industrial Revolution began in the 18th century, ushering in the widespread human use of fossil fuels, the amount of carbon dioxide in the atmosphere has risen by 100 parts per million.
That means human activities are putting carbon dioxide into the atmosphere about 14,000 times as fast as natural processes do, Zeebe said.
And it appears to be speeding up: the U.S. government reported last week that in 2007 alone, atmospheric carbon dioxide increased by 2.4 parts per million.
The natural mechanism will eventually absorb the excess carbon dioxide, Zeebe said, but not for hundreds of thousands of years.
"This is a time period that we can hardly imagine," he said. "They are way too slow to help us to restore the balance that we have now basically distorted in a very short period of time."
