It's not just craters purportedly dug by aliens in Russia, it's also megaslumps, ice that burns and drunken trees. The ongoing meltdown of the permanently frozen ground that covers nearly a quarter of land in the Northern Hemisphere has caused a host of surprising arctic phenomena.



Temperatures across the Arctic are warming roughly twice as fast as the rest of the globe, largely due to the reduction in the amount of sunlight reflecting off of white, snow-covered ground. "At some point, we might get into a state of permafrost that is not comparable to what we know for 100 years or so, some new processes that never happened before," says geologist Guido Grosse of the Alfred Wegener Institute for Polar and Marine Research in Germany.



The mysterious craters in far northern Russia are just such an example. "There is nothing described in the scientific literature than can really, fully explain those craters," says Grosse, who is headed to the Lena River Delta in Siberia this summer, which hosts a joint German-Russian research station. The most likely explanation for the newly discovered craters in Russia is an accumulation of methane over centuries or more that then burst out of the thawing ground sometime in the last few years. "High pressure built up and [the ground] literally popped open," explains biogeochemist Kevin Schaefer of the U.S. National Snow and Ice Data Center. "If it is indeed caused by melting methane ice, we should expect to see more."



These craters will then become lakes, which further thaw the permafrost around and beneath them as the water traps yet more heat from the sun. Similar new lakes are forming in depressions in the newly thawing lumpy landscape across the Arctic known as thermokarst. Such thermokarst lakes and surrounding marshes create the muddy conditions favoring microbes that break dead plant material down into methane. That methane then bubbles out of the lakes and ground and, where concentrated, can even be lit on fire, leading to cases of flames dancing above the ice.



Even more widespread than blast craters or burning ice are drunken trees. When permafrost thaws, soil that was once as solid as concrete becomes mud, due to the fact that ice makes up as much as 80 percent of the ground in some parts of the Arctic. And because ice takes up more space than water, the ground subsides, causing trees that grew upright to lean as the ground liquefies beneath them. Whole forests have listed like an army of drunkards as a result. This is also bad news for modern infrastructure in the Arctic as well: Roads, pipelines and building foundations sink into mud and crack or entire landscapes subside. "Long term, there are huge economic and social impacts to permafrost degrading," Schaefer notes.



Where the ground slopes, even worse can occur: slumps, which are like slow-moving mudslides that can undermine areas of 40 hectares or more and stretch more than a kilometer across. The largest megaslumps can eat into the landscape at rates of a kilometer per decade and seem to show no signs of stopping. One slump in Russia that has mystified scientists extends more than 70 meters deep into the permafrost and is still growing after starting in the 1970s, Grosse says.



Perhaps the biggest concern of thawing permafrost is a massive and sudden release of methane from the Arctic Ocean and/or permafrost. Methane traps at least eight times more heat than carbon dioxide over decades, driving global warming even faster. The bad news on the belch front are noticeable upticks in the amount of methane produced in the Arctic—an increase of roughly 8 percent over 30 years at the Canada’s Alert Station in the Northwest Territories. And ocean expeditions have observed methane bubbling out of methane ice at the bottom of the Arctic Ocean. The good news is that satellite data encompassing broad swathes of the Arctic and stretching back for decades now shows little change in atmospheric concentrations of the potent greenhouse gas. "Why that is, we don't know yet," Grosse says.



Most of the greenhouse gases released by this Arctic thaw will be CO2. And the permafrost thaw will continue as rising levels of greenhouse gases in the atmosphere trap ever more heat, kicking off a feedback cycle that then further melts the Arctic. By mid-century, computer simulations predict that as much as a third of the permafrost area in Alaska could thaw, at least at the surface, with similar amounts in Canada and Siberia. Once the melt has kicked in—and the frozen dead plants that make up the top three meters or so of the permafrost become food for microbes that release CO2—the process is irreversible. "You can't refreeze it," Schaefer says. "Once the decay turns on you can't turn it off, and it persists for centuries."



The permafrost already holds vast stores of carbon, as much as 1.7 trillion metric tons according to estimates—or more than twice as much as is currently in the atmosphere today. Not all of that will thaw in the near future—some areas of permafrost extend 700 meters deep—but as much as 120 billion metric tons could be released by 2100. That's enough to raise global average temperatures by nearly a third of a degree Celsius. "These are big numbers," Schaefer notes. But "they are in fact small when compared to those projected from burning coal and oil and natural gas. Those emissions are just immense."



The computer models that deliver these estimates of how much of that carbon might come out assume a gradual thaw of the permafrost. That prediction could prove erroneous, based on observations to date. Already, thawing processes like slumps and lakes are happening faster and affecting larger regions than expected. As Grosse puts it: "we might be very conservative in our estimate."



Thawing sets in motion a set of complex natural forces, some of which could run counter to the seemingly inexorable warming trend. Trees and shrubs will continue to move north, thanks to warmer temperatures and a longer growing season. Those trees in turn suck CO2 out of the air. NASA’s new Orbiting Carbon Observatory should help clarify how much CO2 this greening of the Arctic will draw down. And even the thermokarst lakes may be burying some carbon, at least over thousands of years as lake sediments bury dead plants and algae.



Even the amount of thawing guaranteed by greenhouse emissions to date remains unclear. "We are trying to figure that out," Schaefer says. And the very rules that have governed Arctic processes during the last 100 years or so of modern exploration may no longer hold. The speed of this ongoing meltdown could accelerate and happen in decades or slowly thaw over centuries and millennia. "What are the limits of permafrost thaw?" Grosse asks. "We don't really know."



There are attempts to expand the monitoring of the Arctic, but huge gaps persist because of its vast extent and harsh conditions. As in most sciences, observations to date are limited to where it is easy for scientists to get to, rather than where one would place monitoring to ensure maximum coverage. Of emerging research questions surrounding the Arctic in the Anthropocene—a putative new geologic epoch tied to relatively recent human impacts on the planet of planetary scope—the fate of the permafrost looms large as a known unknown, as the National Academy of Sciences acknowledged in a report this past April.



One thing is clear, however: the Anthropocene has proved unfriendly to ice so far, and that will get worse as a new Arctic emerges. "This situation is unprecedented," Schaefer says. "The faster you burn fossil fuels, the faster the Arctic is going to warm."