It’s no secret that climate change is melting Earth’s ice caps and glaciers. In many cases, the ice is disappearing right before our eyes. Less well known has been what’s happening below ground. A first-of-its kind global survey has just revealed that the planet’s permafrost is also warming. Scientists now worry that could help make the planet even hotter.
Permafrost is frozen soil, but not the type you might find in your yard in winter. This soil has to stay frozen constantly for at least two years to qualify as permafrost. Near the poles and high in the mountains, some permafrost has remained frozen since the last ice age ended thousands of years ago. And we’re not just talking about a thin layer of soil. In many places, permafrost is more than 10 meters (33 feet) thick, notes Boris Biskaborn. He’s a polar researcher at the Alfred Wegener Institute in Potsdam, Germany.
But this frigid dirt is in danger. Since the Industrial Revolution, the planet has been warming. On average, Earth has warmed by about 1 degree Celsius (1.8 degrees Fahrenheit) since 1850. Air temperatures in polar regions, especially the Arctic, have warmed even more. Over time, this extra heat has gradually soaked into the ground, warming it, too.
In many places, the effects of thawing permafrost are obvious. Once-stable shorelines have been tumbling into the sea. Once-frozen landscapes are turning to mush. Such changes can undermine roads and weaken the foundations of buildings. But Biskaborn and his colleagues wanted to assess less-obvious sites, ones far underground.
They turned to soil collected from a number of deep boreholes. Some bores had been drilled by other teams many years ago, for various studies. Others were drilled more than a decade ago as part of a two-year-long study of polar regions. The holes were bored in North America, Europe, Asia and Antarctica. In all, the team identified more than 120 boreholes where the data record covered a decade. That 10-year period stretched from 2007 through 2016.
Close to the surface, soil temperature changes with the seasons. But if you dig far enough down, you’ll reach a depth where the permafrost temperature stays the same year-round. For each borehole, the team found that depth. It was usually at least 10 meters (33 feet) underground.
Then the researchers looked at how permafrost temperature at that depth had changed over time. In soils from 40 of the boreholes, permafrost temperature had been stable from 2007 through 2016. In 12 of the holes, the permafrost cooled slightly. But in 71 boreholes, permafrost temperature warmed quite a bit.
Biskaborn’s team reported its findings January 16 in Nature Communications.
Not so permanent?
In northern North America, permafrost warmed up an average of 0.23 degree C (0.41 degree F). In northern Asia, frozen soil warmed up by 0.33 degree C (0.59 degree F). In mountainous regions, permafrost warmed by 0.19 degree C (0.34 degree F). Worldwide, the planet’s permafrost has warmed an average of about 0.29 degree C (0.52 degree F).
Half a degree Fahrenheit doesn’t sound like a lot of warming. But it may not take much to melt some permafrost. In five of the boreholes, soil temperature rose above freezing (0 °C, or 32 °F). At these sites, the permafrost had thawed.
When permafrost thaws, it can have consequences far beyond the local landscape, notes Ted Schuur. He’s an ecosystems ecologist at Northern Arizona University in Flagstaff. Yes, he notes, when permafrost on the ground’s surface thaws, it affects roads, bridges and buildings. But it also affects lakes, streams and other ecosystems. For example, when permafrost thaws, shrubs can take hold and grow. That, in turn, means the landscape can support more herbivores such as moose, hares and birds.
And there’s more. Permafrost holds the remains of plants that lived and died long ago. While they were alive, those plants took up carbon from the atmosphere, just as plants do today. But thawing permafrost could unlock that carbon. If ice melts and the water drains away, that lets oxygen reach the dead plants. Now they can start to decompose.
Their rotting may generate vast amounts of carbon dioxide, explains Schuur. It could also support the growth of methane-making microbes in the soil. As those microbes thrive, they will release large amounts of methane, another climate-warming greenhouse gas. This might make global climate change even worse. This is why effects of thawing permafrost can affect people living as far away as the tropics, Schuur says.
A few years ago, he was part of a team that in 2015 estimated the possible effects of thawing permafrost. They used detailed computer programs for their study. By the year 2100, they estimated, thawing permafrost could release enough carbon dioxide and methane to raise the average global temperature by 0.13 to 0.27 degree C (0.23 to 0.49 degree F).
That increase, Schuur notes, would be in addition to any boost in global temperatures from the greenhouses gases that factories and farms emit during that time. And it would be on top of the 1 degree C (1.8 degrees F) that average temperatures have already risen since 1850.
“Warming permafrost is a largely unknown dimension of climate change,” Schuur says. The new study shows that deep underground in chilly, remote parts of the world, big changes may be brewing.
Antarctica A continent mostly covered in ice, which sits in the southernmost part of the world.
Arctic A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice. The high Arctic is that most northerly third of this region. It’s a region dominated by snow cover much of the year.
atmosphere The envelope of gases surrounding Earth or another planet.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
borehole A hole drilled deep into the ground to extract a core of soil, ice or rock. Sometimes the hole is drilled with the goal of getting to gas or pools of liquid, such as water or crude oil.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
climate The weather conditions that typically exist in one area, in general, or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
dimension Descriptive features of something that can be measured, such as length, width or time.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.
glacier A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.
greenhouse gas A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.
ice age Earth has experienced at least five major ice ages, which are prolonged periods of unusually cold weather experienced by much of the planet. During that time, which can last hundreds to thousands of years, glaciers and ice sheets expand in size and depth. The most recent ice age peaked 21,500 years ago, but continued until about 13,000 years ago.
Industrial Revolution A period of time around 1750 that was marked by new manufacturing processes and a switch from wood to coal and other fossil fuels as a main source of energy.
latitude The distance from the equator measured in degrees (up to 90). Low latitudes are closer to the equator; high latitudes are closer to the poles.
methane A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
permafrost Soil that remains frozen for at least two consecutive years. Such conditions typically occur in polar climates, where average annual temperatures remain close to or below freezing.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
survey to view, examine, measure or evaluate something, often land or broad aspects of a landscape. (with people) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.