Researchers are investigating large craters of melting permafrost in northern Canada, which they say are both a consequence of climate change and a contributing factor.

Scientists say warming temperatures are melting a previously frozen layer under the surface in Fort McPherson, N.W.T. Frozen organisms in that surface are now being exposed to the air, producing carbon dioxide and contributing to the greenhouse effect.

"We know there is twice as much carbon locked up in permafrost as there is carbon dioxide in the atmosphere," says Suzanne Tank, a researcher and assistant professor at the University of Alberta.

"So certainly there is the potential there for this carbon, if it's released as carbon dioxide, to have a really huge effect on greenhouse gasses and climate warming."

Scientists are looking to collect samples from the craters to gain more information about the problem, which they call a "sleeping giant."

"There is this uncertainty associated with what this sleeping giant is going to look like," says Tank.