As the Arctic's permafrost continues to thaw due to global warming, all sorts of ancient afflictions, once trapped by the cold, threaten to re-emerge. For instance, scientists have already discovered viruses in melting layers of frozen soil that were believed to have been extinct for tens of thousands of years.

So far, none of these ancient viruses have proven to be contagious for humans. But scientists now fear that melting permafrost threatens to re-animate a more recent scourge, one that scientists thought had been eradicated: smallpox.

Though the eradication of smallpox has been heralded as one of the great accomplishments of modern medical science — there have been no documented cases since 1977 — scientists are concerned that the virus could lie dormant, frozen within permafrost graveyards.

Case in point, after a small Siberian town experienced a devastating outbreak of smallpox in the 1890s, hundreds of bodies were buried in a graveyard along the banks of the Kolyma River. This summer, which has brought record heatwaves in the region, permafrost has been melting at three times the normal rate, and some of those Kolyma River corpses have become exposed. Scientists were able to visibly identify smallpox sores on the well-preserved tissues of the corpses, according to the Siberian Times.

Luckily no intact viruses were found from samples taken at the site, but researchers did find traces of smallpox DNA. That at least leaves open the possibility that a complete virus could have survived.

"This type of research should go on," urged Sergey Netesov, chief of the bionanotechnology, microbiology and virology laboratory at the natural sciences department of Novosibirsk State University. "Examining deeper burials might help clear up the situation."

It's a frightening prospect, an unexpected consequence of global warming. If smallpox does lie dormant somewhere in the Arctic's vast permafrost, we may not find out until it re-enters the human population. There's no telling what other deadly diseases may be exposed along with it.