Thermokarsts: The emissions-releasing landscapes absent from most climate models

Across the Arctic Circle, the unruly forms and faces of thawed permafrost landscapes known as thermokarsts – pocketed wetlands, hissing and bubbling lakes, or icy eroding hillsides – are becoming increasingly common. Yet, while thermokarsts are critically important indicators of stored greenhouse gas emissions being uncorked by climate change, they’re receiving disproportionately little attention.

About 24 percent of exposed land in the Arctic Circle is covered by permafrost – soil, rocks and sand bound together by ice. Much of it has been frozen solid for tens of thousands of years, creating one of the largest carbon sinks in the world, currently estimated to hold around 1.5 trillion tons of carbon. The material also keeps a host of microbes, including potentially-harmful bacteria and viruses, in a dormant state.

As global temperatures rise, some of that permafrost is melting. Most climate models to date predict a very gradual melt occurring over the course of decades or centuries, and many project that the Arctic will effectively remain carbon-neutral because of the increase in plant growth at warmer temperatures.

Water has less volume than ice, so when permafrost melts, the process creates a pock-marked landscape of depressions called thermokarsts. In flatter lowland areas, these depressions tend to retain the water and become lakes, while in mountainous areas they are more likely to cause erosion. The resulting uneven landscapes expose more of the permafrost’s surface area to the air, causing the melting to escalate further.

The process is “affecting landscapes in unprecedented ways,” said Merritt Turetsky, director of the Institute of Arctic and Alpine Research at the University of Colorado Boulder (CU), in a press release about a new study on the topic that was released last month. “Systems that you could walk on with regular hiking boots and that were dry enough to support tree growth when frozen can thaw, and now all of a sudden these ecosystems turn into a soupy mess.”

The changes are already affecting people’s lives and livelihoods in the North. “Some thermokarsts can be really sudden,” says Niels Weiss, a research associate at Wilfrid Laurier University in Yellowknife, Canada. “So over the course of the summer you might get a new lake, or it might be a whole slope that starts to erode and slump off onto a road or infrastructure or houses,” he says. “It’s a really big issue for the communities here.”

But it’s not just local communities who should be concerned, says Weiss: there may well be global implications, due to thermokarsts’ impact on carbon emissions. In thermokarst lakes, microbes in the soil begin to munch on the ancient sediments and organic matter, producing carbon dioxide and methane, which bubble to the surface and release into the atmosphere. The same thing can happen after thermokarst-based erosion, when carbon from melted permafrost is transported into other waterways.  

While a 2018 study by researchers at the University of Fairbanks Alaska briefly drew international attention to the potential impact of thermokarsts on emissions, no current climate models take them into account, and only a few models take permafrost thaw into consideration at all. According to the CU study, this is a glaring omission: the researchers estimate that if climate modelers include these phenomena, projections of permafrost emissions this century could be more than double what was previously thought. If so, these emissions would rival the amount generated from land-use change such as deforestation and forest fires – which, after fossil fuels, are the second-highest human source of emissions.

The findings highlight the importance of quick action to include thermokarsts in climate models, and of ‘upping our game’ in cutting emissions from other sources. “We can definitely stave off the worst consequences of climate change if we act in the next decade,” said Turetsky. “We have clear evidence that policy is going to help the North and thus it’s going to help dictate our future climate.”