Earth's climate more sensitive to CO2 than thought: study

Earth's climate may be more sensitive to increased carbon dioxide than previously thought, according to a new study that suggest the impact of greenhouse warming has been significantly underestimated.
Researchers from Binghamton University in US examined nahcolite crystals found in Colorado's Green River Formation, formed 50 million years old during a hothouse climate.
They found that carbon dioxide levels during this time may have been as low as 680 parts per million (ppm), nearly half the 1,125 ppm predicted by previous experiments.
The new data suggests that past predictions significantly underestimate the impact of greenhouse warming and that Earth's climate may be more sensitive to increased carbon dioxide than was once thought, said Tim Lowenstein, professor at Binghamton University.

"The significance of this is that carbon dioxide 50 million years ago may not have been as high as we once thought it was, but the climate back then was significantly warmer than it is today," said Lowenstein.
Carbon dioxide levels in the atmosphere today have reached 400 ppm. According to current projections, doubling the carbon dioxide will result in a rise in the global average temperature of 3 degrees Celsius.

This new research suggests that the effects of carbon dioxide on global warming may be underestimated.
"Take notice that carbon dioxide 50 million years ago may not have been as high as we once thought it was," said Lowenstein.

"We may reach that level in the next century, and so the climate change from that increase could be pretty severe, pretty dramatic. Carbon dioxide and other climate forcings may be more important for global warming than we realised," he said.
The only direct measurement of carbon dioxide is from ice cores, which only go back less than 1 million years.
The researchers are trying to develop ways to estimate ancient carbon dioxide in the atmosphere using indirect proxies.
Lowenstein said that their approach is different than any ever undertaken.
"These are direct laboratory experiments, so I think they're really reliable," he said.

The study was published in the journal Geology.