Entirely Out Of Equilibrium
Scientists have found new evidence that the Earth's natural feedback mechanism regulated carbon dioxide levels for hundreds of thousands of years.
But they say humans are now emitting CO2 so fast that the planet's natural balancing mechanism cannot keep up.
The researchers, writing in the journal Nature Geoscience, say their findings confirm a long-believed theory.
Carbon spewed out by volcanoes is removed from the air by rock weathering and transported to the ocean floor.
Using evidence from an Antarctic ice core, the team calculated that over a period of 610,000 years the long-term change in atmospheric CO2 concentration was just 22 parts per million (ppm), although there were larger fluctuations associated with the transitions between glacial and interglacial conditions.
By comparison, two centuries of human industry have raised levels by about 100 ppm - a speed of rise about 14,000 times faster.
"These long term cycles are way too slow to protect us from the effect of (anthropogenic) greenhouse gases," said Richard Zeebe from the University of Hawaii in Honolulu.
"They will not help us with our current CO2 problem. Right now, we have put the system entirely out of equilibrium."
The Nature Geoscience abstract and the firewalled article are available here.