The ocean's thermohaline circulation occurs when both temperature and salinity act together. Thermohaline circulation is vertical circulation induced by surface cooling, which causes convective overturning and consequent mixing.

Even the most strict climate policy would still leave a 25 percent chance of a thermohaline collapse, the study suggests.

"This is a dangerous, human-induced climate change," said Michael Schlesinger, a UI professor of atmospheric sciences. "The shutdown of the thermohaline circulation has been characterized as a high-consequence, low-probability event. Our analysis, including the uncertainties in the problem, indicates it is a high-consequence, high-probability event."

Schlesinger presented his findings Thursday during the United Nations Climate Control Conference in Montreal, Canada.