A team of scientists has analysed evidence from a prehistoric event and come to the conclusion that the Earth may be able to recover from rising carbon dioxide emissions faster than previously thought.
The study led by a Purdue University team showed that when faced with high levels of atmospheric carbon dioxide and rising temperatures 56 million years ago, the Earth increased its ability to pull carbon from the air.
This led to a recovery that was quicker than anticipated by many models of the carbon cycle - though still on the order of tens of thousands of years, Gabriel Bowen, the associate professor of earth and atmospheric sciences, who led the study, said.
"We found that more than half of the added carbon dioxide was pulled from the atmosphere within 30,000 to 40,000 years, which is one-third of the time span previously thought," Bowen, who also is a member of the Purdue Climate Change Research Center, said.
"We still don't know exactly where this carbon went, but the evidence suggests it was a much more dynamic response than traditional models represent," he explained.
Bowen worked with James Zachos, a professor of earth and planetary sciences at the University of California, Santa Cruz, to study the end of the Palaeocene-Eocene Thermal Maximum, an approximately 170,000-year-long period of global warming that has many features in common with the world's current situation.
"During this prehistoric event billions of tons of carbon was released into the ocean, atmosphere and biosphere, causing warming of about 5 degrees Celsius," Bowen said.
"This is a good analogue for the carbon being released from fossil fuels today," he explained.
Scientists have known of this prehistoric event for 20 years, but how the system recovered and returned to normal atmospheric levels has remained a mystery.
Bowen and Zachos examined samples of marine and terrestrial sediments deposited throughout the event. The team measured the levels of two different types of carbon atoms, the isotopes carbon-12 and carbon-13.
The ratio of these isotopes changes as carbon dioxide is drawn from or added to the atmosphere during the growth or decay of organic matter.
Plants prefer carbon-12 during photosynthesis, and when they accelerate their uptake of carbon dioxide it shifts the carbon isotope ratio in the atmosphere.
This shift is then reflected in the carbon isotopes present in rock minerals formed by reactions involving atmospheric carbon dioxide, Bowen said.
"The rate of the carbon isotope change in rock minerals tells us how rapidly the carbon dioxide was pulled from the atmosphere," he said.
"We can see the fluxes of carbon dioxide in to and out of the atmosphere.
"At the beginning of the event we see a shift indicating that a lot of organic-derived carbon dioxide had been added to the atmosphere, and at the end of the event we see a shift indicating that a lot of carbon dioxide was taken up as organic carbon and thus removed from the atmosphere," he said.
A paper detailing the team's National Science Foundation-funded work was published in Nature Geoscience.