The reason why scientists are so worried about this issue is because there is evidence that a super-greenhouse effect occurred 55 million years ago, during what is called the Palaeocene–Eocene Thermal Maximum (PETM). During this hot-house event, scientists think that up to 1,500 Gt of gas hydrates may have been released. This huge injection of CH4 into the atmosphere accelerated the natural greenhouse effect, producing an extra 5°C of warming.
