Humanity is facing a new pandemic threat, scientists have warned. Ancient viruses frozen in Arctic permafrost (the permanently frozen layer on or below the Earth's surface) could one day be released as the Earth's climate warms and cause a major outbreak of disease, they say.

Methuselah germs - or zombie viruses as they are also known - have now been isolated by researchers who have declared that a new global medical emergency could be triggered.

Permafrost covers one-fifth of the Northern Hemisphere and consists of soil that has been at sub-zero temperatures for long periods. Some layers have remained frozen for hundreds of thousands of years, scientists have discovered.

But permafrost is changing. The upper layers - in Canada, Siberia and Alaska - are melting as a result of the climate. Scientists believe that permafrost – at its deepest levels – may contain viruses that are up to a million years old and thus far older than our own species, which is thought to have emerged around 300,000 years ago.

Our immune systems may never have been in contact with some of those microbes, and that's another concern.

For this reason, many scientists are working with UArctic, the University of the Arctic - an international educational network in the polar region - to create quarantine facilities and provide medical expertise that can identify early cases and treat them at the level local to keep the infection under control.