Trillions upon trillions of microbes have remained locked away in the Arctic’s permafrost, undisturbed and suspended in a “deep sleep” for thousands of years. But could climate change soon start to change that? 

The Arctic is warming twice as fast as the rest of the world in the wake of climate change. With these rising temperatures, much of the environment’s ice, glaciers, and permafrost is thawing away. Like most water on Earth, the frozen water is known to harbor an incredible amount of microbial biodiversity, from viruses and bacteria to fungi and algae.

Since up to 25 percent of Earth's terrestrial surface is underlain by permafrost, it looks likely that many of these species will be unknown to human understanding. Earlier this year, scientists published preliminary results looking at the ancient viruses trapped inside samples taken from 15,000-year-old ice from the Guliya ice cap on the northwestern Tibetan Plateau in Asia. Their analysis of the ice core samples revealed over 30 virus groups, 28 of which were new to science.

Understandably, this has raised questions about whether infectious diseases could possibly emerge or reemerge from thawing permafrost and ice. 

The Yamal Peninsula in the depths of Siberia was notorious for its recurring outbreaks of anthrax in the early 20th century, leading to the infection that became known as “Yamal disease”. However, major outbreaks had largely become a thing of the past thanks to deer vaccinations and a better understanding of the disease. 

But then, in 2016, an outbreak took hold once again, causing dozens of people to fall sick with the bacterial infection and killing at least one boy. Officials contested that a heatwave had melted permafrost in the area and exposed an infected reindeer carcass in the Siberian tundra, leading to sensational headlines of a “Siberian plague” resurrected by climate change. While scientists have since tried to quell those fears by suggesting the outbreak was most likely linked to population growth in the area and a drop in deer vaccination, it reignited the debate about whether long-lost microbes could return to infect humans once again. 

Recent decades have also seen mounting fears that the permafrost-buried bodies of people who died in previous pandemics could come back to haunt humanity. Back in the 1950s, scientists discovered the body of a woman who died during the “Spanish flu” pandemic in 1918, buried in the Alaskan permafrost. By 1997, scientists had even managed to recover enough viral RNA to sequence the 1918 H1N1 strain in its entirety. Some have raised similar worries about the thawed bodies of people who died from smallpox, a disease that's been eradicated. 

Of course, there’s no guarantee that any revived microbe could infect humans or any other mammals. Back in 2015, French scientists found a 30,000-year-old giant virus, dubbed Mollivirus sibericum, in the thawing permafrost of far northeast of Siberia and managed to revive it back to life, even prompting it to infect an amoeba. This raised a fair amount of media hype, but many pointed out that fears this virus could infect humans were overblown, as it was only shown to infect amoeba.

Beyond concerns of ancient viruses springing back to life to infect humans and other mammals, there is the much more certain threat that comes with thawing permafrost and microbial life. As many have highlighted in recent decades, the question is not just how climate change might affect these microorganisms, but how these freshly revived lifeforms might affect the climate. As these millions of microorganisms come back to life, they will begin to respire once again, releasing massive amounts of carbon dioxide and methane into the atmosphere. Predicting how this might affect the planet’s atmosphere and climate is immensely complex, but it’s clear that thawing permafrost is already releasing significant quantities of greenhouse gases. 

In an ironic turn of events, this would theoretically deepen the planet’s climate crisis and lead to even more melting permafrost.