They call it flammable ice, and it could be the world's last great source of carbon-based fuel - assuming we can mine methane hydrates, crystal lattices of ice that trap methane beneath ocean beds and permafrost. One problem with extracting this methane is that you have to melt the ice to bring the gas to the surface. In 2002, a team of geologists from Canada and Japan tried injecting hot water into the ice beneath the delta of the McKenzie river in northern Canada. While this released some hydrates, it used a lot of energy.