A large part of the Arctic is covered by permafrost, essentially frozen ground, that makes up almost a quarter of the northern hemisphere. However, it is warming at a rapid rate, which is bad news for the climate beyond rising sea levels. When permafrost melts, it releases large amounts of carbon dioxide and methane (both greenhouse gases) into the atmosphere. Methane is 22 times more potent as a greenhouse gas than carbon dioxide. Scientists are studying the effects of this melting to better predict how quickly the planet will change as a result of global warming.