The Permafrost Tunnel Research Facility, dug in the mid-1960s in Fairbanks, Alaska, allows scientists a three-dimensional look at frozen ground.

The Permafrost Tunnel Research Facility, dug in the mid-1960s in Fairbanks, Alaska, allows scientists a three-dimensional look at frozen ground. / NASA

In 2018, we reported on concerns that zombie pathogens — ancient bacteria and viruses that could potentially rise from the dead and threaten humans if the layers of frozen permafrost where they're buried thaw as the Earth warms. The consensus among the scientists interviewed was: It's unlikely — although there was one tantalizing anecdote about a scientist whose knee may have become infected after contact with a defrosted seal. But we did want to follow up and see what the latest research says about thawing permafrost — and have learned of another threat posed by its demise.

It's not just warmer temperatures that pose a problem for the permafrost. Scientists are now investigating whether rainfall could be causing serious issues in the Arctic's permafrost – with repercussions for humans.

Since 2013, Fairbanks, Alaska, has had two of the wettest years in recorded history. A total ofo 14.6 inches of rain fell in the summer of 2014; it was the wettest summer yet. And that's not a good thing for permafrost, says Thomas Douglas, a geochemist in the U.S. Army Corp of Engineers.

Permafrost — completely frozen ground composed of materials like soil, rocks and even bones and plants — makes up a nearly a quarter of the Northern Hemisphere. Much of it has been frozen for thousands of years.

Warming temperatures have begun to thaw permafrost, and now, increased rainfall seems to be intensifying the problem, according to Douglas' latest study in Climate and Atmospheric Science, published in July.

"In general, across the arctic, the thought is that things are getting wetter," Douglas says, but particularly in Fairbanks. "2014 and 2016 were the #1 and #3 summer precipitation years in what was then a 90-year record. Shattering records like this is just really unique."

To figure out how this increased rainfall affects permafrost, Douglas and his team studied three permafrost sites for five years. He and his team focused on "active layer" permafrost, the very top layer of permafrost that naturally thaws in the summer and refreezes in the winter.

To study this layer, his team measured how deep it went at the end of each summer, right when the permafrost was at maximum thaw. They made the measurements using a frost or thaw probe.

"We take a metal rod with a handle on it and we shove it down into the ground until it makes a thump noise," Douglas explains. That's when they know they've hit frozen permafrost. A ruler on the side of probe tells the user how far down the rod is in the ground.

Between 2013 and 2017, the team took more than 2,500 measurements — and they started to see a pattern. The more it rained, the more the layer of thawed permafrost grew in the summer.

The thaw was worse in some locations more than others, depending on the terrain where measurements were taken. Forests and mossy landscapes seemed to protect the permafrost. There, for every additional inch of rain, the permafrost thawed by an additional quarter of an inch.

But in locations where human activity – such as trails and clearings — had altered the land, the thaw was worse. For every additional inch of rain, the researchers saw an additional inch of thaw. At one particular site, permafrost thaw depth grew from 47 inches in 2013 to nearly 75 inches in 2017.

Douglas explains, "When you remove vegetation, that's like leaving the lid open on your cooler on a summer day. It allows heat and water to get down in the permafrost pretty rapidly."

Out of all the team's research, Douglas says their most important finding was that thinner layers of thawed permafrost seem to be vanishing — literally thawing away.

"Once it started to thaw, even when we had some slightly drier summers, we never got back to the shallower thaw depths we started out with [in 2013,]" he says. "Our sense is that unless we get a really cold winter, or a couple of really cold winters in a row, it's probably not coming back again."

Dmitry Streletskiy, a professor at George Washington University who specializes in permafrost, says that Douglas's study is a great contribution to permafrost research. However, he emphasizes that the study was conducted in a boreal ecosystem, a sub-arctic region with warmer temperatures and relatively warm permafrost.

"It's still below freezing, but it is kind of considered dying permafrost, and it's not how things work in the arctic tundra," Streletskiy says, where temperatures are colder. "Their findings are applicable to the particular environment they studied, and we cannot extrapolate them to the entire arctic."

Permafrost in boreal regions is weak, Streletskiy explains, and many factors can contribute to its thaw, including heavy rainfall in the summer. "However, in the high arctic, precipitation closer to the fall can be a good thing and can increase ice content to build protection."

Still, Streletskiy agrees that permafrost is degrading on a global scale due to climate change. Its impacts are starting to show — and zombie pathogens shouldn't be our only concern.

He and Douglas both point to the Norilsk oil spill in Russia, where an oil tank spewed more than 150,000 barrels of diesel into the arctic, and officials have been racing to clean it up. Many experts believe thawing permafrost is to blame; the oil tank, which sat on permafrost, collapsed in May.

What's more, permafrost thaw can lead to deterioration in infrastructure, such as pipelines, railroads and homes, Streletskiy explains. "Small changes in temperature can affect how much weight a foundation built on permafrost can support. Say for example at -10 degrees, the foundation can support 100 tons, but at -8 degrees, it can only support 50 tons."

For people who don't live near the oil spill or in arctic regions, it's easy to forget about permafrost. "Out of sight, out of mind," Douglas says. But the thaw could one day affect everyone.

An estimated 1,400 to 1,600 billion metric tons of carbon are currently frozen in the permafrost. "There are a lot of questions about what's going to happen when that [carbon]starts to thaw," Douglas says.

According to the 2019 Arctic Report Card, warming climates are already converting this carbon into greenhouse gases that are being released into the atmosphere — and they have the potential to accelerate climate change. As the permafrost where the carbon is encased thaws, the carbon can transform into carbon dioxide and methane gases, which are well-known for their ability to trap heat in the earth's atmosphere — and for their potential to accelerate climate change.

Streletskiy says, "That's why everyone should be concerned, regardless of whether they live in Australia or America, because this will contribute to global warming."

Nadia Whitehead is a freelance journalist and science writer. Her work has appeared in Science, The Washington Post and NPR. Find her on Twitter@NadiaMacias.

Copyright 2020 NPR. To see more, visit