Gas hydrates could be a "serious geohazard in the near future due to the adverse effects of global warming on the stability of gas hydrate deposits," the Benfield Hazard Research Center said in a report.

A big release of methane could speed up global warming far beyond the levels forecast in current models, upping the risk of floods, droughts and wildfires, the report said.

"The big problem is that a warmer world is a less predictable world," Mark Maslin, the report's author, told Reuters.

U.N. reviews of climate change had not taken enough account of the threat from gas hydrates, he added.

Methane is 21 times more powerful as a greenhouse gas than carbon dioxide, the main gas blamed for driving up temperatures, the report said. Carbon dioxide is largely released from burning fossil fuels, from cars to factories.

Hydrate thawing in permafrost regions such as Alaska could also lead to a range of local difficulties.

"Alaska (a permafrost region) is already finding problems with subsidence of buildings and destabilization," said Maslin.

The Kyoto protocol, the main international plan for reining in emissions of carbon dioxide and gases like methane, is dependent on Russian backing after a U.S. pull-out.

But President Vladimir Putin has said Russians might benefit from a warmer world.