Binghamton University Professor Tim Lowenstein's concerns are rooted in his and Professor Robert Demicco's discovery of nahcolite -- a rare carbonate mineral that formed during the Eocene Epoch, the warmest period on Earth during the last 65 million years.

Lowenstein and Demicco said nahcolite suggests Eocene warming was concurrent with atmospheric carbon dioxide levels of at least 1,125 parts per million, which is 3 times current CO2 levels, but not much higher than what's expected on Earth in about 100 years.

"Right now, we're on a predictable pace," said Lowenstein. "But there will likely be tipping points -- unexpected events that could really change things -- so all of a sudden we may get changes in ocean circulation that we never would have predicted, or the tundra may melt.

"Some unexpected event is going to occur that's going to be more dramatic than the progressive changes that occurred over the last 100 years."

If we keep doing what we're doing now, we will be up to the CO2 levels of the Eocene within another 100 or 200 years," he said, adding that "hothouse" world of 50 million years ago should serve as a reminder of what global changes are possible.