Because permafrost’s icy soil contains frozen carbon — mostly organic matter such as leaves and roots — it releases a lot of carbon, in the form of carbon dioxide and methane, into the atmosphere as it thaws.
Scientists, who are now observing how much of these gases are currently being released from this thawing ground, say that the most worrying part about a warming permafrost is that if the permafrost begins to thaw, it will be impossible to stop.
And if the thawing of the permafrost is not stopped, that will release vast amounts of carbon into the air. Scientists estimate that the permafrost contains two and a half times as much carbon as the entire atmosphere. Current projections for the amount of carbon that the Arctic and sub-Arctic regions could one day annually contribute to the atmosphere are equivalent to anywhere from 15% to 35% of today’s yearly emissions from human activity.
“Even if it’s 5 or 10 percent of today’s emissions, it’s exceptionally worrying, and 30 percent is humongous,” Josep G. Canadell, a scientist in Australia who runs a global program to monitor greenhouse gases, told The New York Times. “It will be a chronic source of emissions that will last hundreds of years.”
Likely to exacerbate the problem are two facts: First, methane, which is often released by thawing permafrost, is more than 20 times more effective than carbon dioxide at trapping heat in the atmosphere. Second, wildfires are becoming increasingly common across the north, and increased burning will further the thawing of the permafrost.
Permafrost ancient and recent history
During the last ice age, western North America and eastern Siberia were not covered in glaciers, but powerful winds and rivers brought in massive amounts of silt and dust to these frigid areas. During the summers, the top layer of this soil would thaw and grasses would grow and take in carbon dioxide. During the winter, organic materials such as grass roots, leaves and even animal bodies would freeze before they could decompose, forming layers of permafrost.
In the last several decades, scientists have been logging permafrost temperatures, and the overall trend is clear: temperatures are rising relentlessly across the region and the northernmost regions are warming the fastest, while the southern areas have shown marked thawing. For instance, the permafrost across much of central Alaska is just below freezing and should see widespread thawing as soon as the 2020s. In the northern regions, the permafrost is still 12 degrees Fahrenheit below freezing.
Scientists are beginning to worry that the thawing of the permafrost changing the land more rapidly than they can understand the changes or make predictions based on them. For example, the region is seeing an increase in a particular land phenomenon called thermokarsts (photographed above).
Thermokarsts form when the thawing permafrost ground turns mushy, causing the land to collapse and often causing a lake or wetland to form. The dark surface of the lake’s water will then capture more heat from the sun and cause the surrounding permafrost to thaw as well. Near thermokarsts, the forests often are called “drunken,” because the trees, whose roots have lost their solid support system, lean crazily.
Thermokarsts are becoming more common in some regions, such as northernmost Alaska, but scientists are not yet sure whether they will become more common throughout the Arctic.
“We expect increased thermokarst activity could be a very strong effect, but we don’t really know,” Guido Grosse, a University of Alaska, Fairbanks scientist, told The New York Times. He is working with another scientist on mapping thermokarst lakes and methane seeps to see if satellites and aerial photography can be used to detect trends.
The roles of methane and wildfires
The first reason the thawing of the permafrost is especially worrisome has to do with methane.
When the permafrost thaws, the organic material trapped in it is consumed by bacteria. If there is air in the area, oxygen-breathing bacteria will break down the organic matter and the carbon will enter the air as carbon dioxide.
But when organic matter breaks down at the bottom of a lake or wetland, then another type of bacteria (methanogens) will break it down, releasing the carbon into the atmosphere as methane.
Although most of the carbon released by the permafrost is likely to be carbon dioxide, scientists say that the fact that methane is so much more potent than carbon dioxide as a greenhouse gas means that it will be likely be responsible for trapping as much heat as the carbon dioxide will.
Another reason scientists are concerned about the thawing of the permafrost is the fact that fires in the tundra are becoming more common as the land, which used to be too damp to burn, dries out.
A 2007 lightning-sparked fire on the Anaktuvuk River in northern Alaska was the first of its size (400 square miles) in 5,000 years. As the Times reports,
Scientists have calculated that the fire and its aftermath sent a huge pulse of carbon into the air — as much as would be emitted in two years by a city the size of Miami. Scientists say the fire thawed the upper layer of permafrost and set off what they fear will be permanent shifts in the landscape.
The paper quotes Michelle C. Mack, a University of Florida scientist who is studying the fire: “I maintain that the fastest way you’re going to lose permafrost and release permafrost carbon to the atmosphere is increasing fire frequency.”
It’s not entirely clear exactly how these changes will impact the Arctic, the permafrost or the planet as a whole. For instance, the thawing permafrost could release nutrients that spur more Arctic plant growth, and those plants then take up some carbon dioxide.
But the scientists studying the area are worried by all the changes.
“To me, it’s a spine-tingling feeling, if it’s really old carbon that hasn’t been in the air for a long time, and now it’s entering the air,” Edward A. G. Schuur, a University of Florida researcher who has done much research in Alaska, told The Times. “That’s the fingerprint of a major disruption, and we aren’t going to be able to turn it off someday.”
photo: The land around these two bays in Northern Siberia is dotted with thermokarst lakes. (NASA Goddard Photo and Video/Flickr)
via: The New York Times