temperature rise not explained entirely by carbon

A team of scientists led by a University of Hawaii oceanographer had a big surprise when they looked to the ancient past for clues to global warming.

Atmospheric carbon increased 70 percent during the period known as Paleocene-Eocene Thermal Maximum 55 million years ago, said Richard Zeebe. Yet it was less than expected to explain a rapid increase in temperatures, he said in an interview.

"This constitutes an enigma because carbon dioxide released cannot account for the entire warming. This means something else contributed significantly to the warming," he said.

"We're not saying carbon dioxide is not important," he emphasized. "It is very important. Current and future warming is almost entirely due to carbon emissions. There is no doubt about this."

However, his team believes other mechanisms could have contributed to the rapid heating during the Paleocene-Eocene Thermal Maximum period, which they said represents "a possible analogue for the future."

"The question is still open by how much the global temperature will increase until the end of the century, depending how much carbon dioxide we put into the atmosphere," Zeebe said.