Ancient bacteria under frozen ground could contain many deadly diseases. The microbes have been trapped for millennia in permafrost. This is ground that stays completely frozen for at least two years. It is common in mountains and near the North and South Poles. The permafrost is melting because of climate change. The result could be the release of unknown, harmful viruses. Scientists are calling these 'Factor X'. A professor in infectious diseases said we know little about Factor X and the biological dangers trapped in Earth's permafrost.

A virologist says there are viruses in the permafrost that are more than 50,000 years old. These could be harmful to humans. The virologist said unknown, "ancient viruses up to a million years old" could be terrifying because we have never seen them before. He added that deadly bacterial diseases like smallpox could be released worldwide. Factor X could be an even bigger problem. However, many scientists say the release of methane is a bigger danger from melting permafrost. Methane is a greenhouse gas that is 80 times more harmful than CO2.