Past warming shows gaps in climate knowledge -study

A dramatic warming of the planet 55 million years ago cannot be solely explained by a surge in carbon dioxide levels, a study shows, highlighting gaps in scientists’ understanding of impacts from rapid climate change.

During an event called the Palaeocene-Eocene Thermal Maximum, global temperatures rose between 5 and 9 degrees Celsius within several thousand years. The world at that time was already warmer than now with no surface ice.
“We now believe that the CO2 did not cause all the warming, that there were additional factors,” said Richard Zeebe, an oceanographer with the University of Hawaii at Manoa.

“There may have been an initial trigger,” he told Reuters on Wednesday from Hawaii. This could be a deep ocean warming that caused a catastrophic release of methane from hydrate deposits under the seabed.

“If this additional warming which we do not really understand, was caused as a response to the CO2 warming, then there is a chance that also a future warming could be more intense than people anticipate right now,” Zeebe said.

He said the study suggested there could be atmospheric or ocean processes as yet unknown or poorly understood that might have accelerated the warming. Possibilities could be changes in ocean currents, a much larger release of methane or even greater impacts from higher CO2 levels than currently thought.

At present, CO2 levels have already risen from 280 parts per million to nearly 390 ppm since the Industrial Revolution and could exceed a 70 percent increase during this century, a rate much faster than the Palaeocene-Eocene event, Zeebe said.

While this would cause initial effects, much worse could follow in the coming decades and centuries as the oceans, land and atmosphere tried to deal with the higher CO2 levels, he said.

Reuters