Thawing Permafrost in the Arctic Will Speed Up Global Warming
There's more carbon locked up in the high north's permafrost than the combined total released into the atmosphere by humans. The big melt going on right now in the Arctic could trigger a train of catastrophic events across the world.
Standing on the shore in Deadhorse, Alaska, looking out on the Arctic Ocean, a thin white line on the horizon divides the dark gray-blue water and the light blue sky. Sea ice. It's late June, and the frozen mass is making its annual retreat here in the land of the midnight sun, a place that may in the next decade experience ice-free summers. A few days earlier oil company workers had spotted a polar bear and her two cubs nearby on the rocky shore--an increasingly common sight as sea ice thins and shrinks and the animals resort to scavenging for food on land. Although these are the images that a warming Arctic typically conjures, dwindling sea ice and starving polar bears are only part of the story. Rising temperatures are already melting the Arctic's permafrost, and an all-out failure of the frozen foundation would not only irrevocably change this fragile landscape but also speed up warming across the earth.
As we drive south from Deadhorse, the flat coastal plains, a summer haven for more than 150 bird species, climb into the rolling foothills of Alaska's North Slope. Here, about 120 miles south of the Arctic Ocean and 160 miles north of the Arctic Circle, scientists at Toolik Field Station have been studying the land, waterways, and wildlife for decades. I'm here on a Marine Biological Laboratory's Logan Science Journalism Fellowship to learn from scientists who have had a front-row seat to the changes already under way in one of the fastest-warming places on the planet.
Take the lightning--a rare phenomenon in 1975, when the station was founded. Now, on any given summer afternoon, piles of thick cumulonimbus clouds build, obscuring the Brooks Range's snow-covered peaks and releasing bright flashes that light up the darkened sky. Scientists have seen lightning strikes increase 20-fold with warmer temperatures, sparking previously unheard-of wildfires in the tundra (see "The Hottest Spot," November 2003). The fires set in motion changes that thaw permafrost, a process well on its way as the region heats up. Permafrost holds water at the surface and creates aquatic habitat in what would otherwise be an arid environment. Unabated melting will drastically reshape the North Slope landscape and have profound effects on fish and wildlife. When ice in the permanently frozen ground liquefies--whether started by large disturbances like fire or small ones like a trickle of water--the ground collapses, forming enormous gullies that can be hundreds of feet wide and long and tens of feet deep. The number of these scars, called thermokarsts, is growing here and throughout the Arctic, freeing up carbon long locked away as the organic matter thaws and decomposes.
The Arctic's soil and permafrost hold nearly twice as much carbon as the earth's atmosphere, dwarfing the amount of carbon emitted to date by burning fossil fuels. Since the industrial revolution our dependence on coal and oil has ratcheted up the atmosphere's carbon content, from 560 to 760 gigatons. Permafrost holds an estimated 1,400 gigatons of carbon. In addition to carbon dioxide, the frozen source is releasing methane, a greenhouse gas 25 times more potent, though it stays in the atmosphere for only a decade rather than for millennia. The gas is bubbling up from land and also from a large, previously overlooked source: permafrost submerged beneath the Arctic Ocean. It's too early to say whether this is a newly observed steady leak, or if it signals the beginning of a flood of methane. But it underscores how important it is to understand whether thermokarsts, fire, or other mechanisms will unleash this stockpile from the frozen north. When it comes to contributors to climate change, we usually talk about coal-fired power plants or deforestation in the Amazon. But sitting at the top of the world is a force for change potentially more powerful than any other ever seen.
It might seem strange to describe a landscape that endures such harsh weather as "delicate," but the tundra hangs in a precarious balance. North of Toolik, for instance, two dark, parallel tracks extend for miles across the tundra. A single vehicle that drove over the bumpy terrain in the 1940s made these marks. More than a half-century later, they're still visible. "The Arctic is a place where everything is about the minutest change in energy balance," says Breck Bowden, a University of Vermont aquatic ecologist. "All it takes is for a vehicle to crush the vegetation, change the albedo--the amount of light that's being reflected away from the surface--make it a little bit darker because the soil is coming through. More energy is absorbed, and that area just continues to melt. And as it continues to melt, a new community of vegetation comes to grow in there, and we now have a permanent scar across the landscape."
Today researchers are seeing wounds across the tundra. Bowden and Michael Gooseff, an environmental engineer at Penn State University, first happened upon a thermokarst near Toolik by accident in 2003. Scouting the Kuparuk, a clear blue river that snakes its way through tundra east of the station, something unusual caught their attention. "We noticed that one of the tributaries was really, really turbid," says Gooseff. "There was lots of muddy water."