Danger of "runaway warming", perhaps spurred by release of oceanic methane hydrates.
Even more worrying, however, is the impact of rising sea temperatures on the far greater reserves of methane hydrates that are found on the sea floor.
He is equally sceptical about methane hydrates, arguing that the energy they contain is less than the energy needed to release and secure it.
"The modeling of methane hydrate is frankly in its infancy," but it seems "robust to conclude" that mankind could "melt a significant fraction of the methane hydrates in the ocean," they wrote.
For simple gas hydrate formation, the temperature and pressure of methane hydrate is highest, butane is lowest, and ethane and propane is between them.
One big unknown is the stage at which dangerous tipping points would be reached that lead to further warming - for example the release of methane hydrate deposits in the Arctic.
The Earth holds other, less-accessible fuels, such as tar sands, and a more exotic possibility in the form of icy methane hydrates.
Throughout the system there would be ways of warming things up and injecting antifreeze to stave off the formation of icelike methane hydrates.
