It is undeniable that our planet is changing. There are many ways that we've witnessed this: more powerful and frequent storms, extreme weather highs and lows, melting ice caps, and ocean acidification, to name a few. Recently, scientists have started to raise the alarm on another way that our planet is changing: our permafrost is melting. While we're unlikely to encounter this issue in our everyday lives it has some profound environmental implications.
Permafrost is defined by the International Permafrost Association as "ground (soil or rock and included ice or organic material) that remains at or below 0°C for at least two consecutive years." Permafrost thickness can vary from less than one meter to more than 1,500 meters below the surface. There are three commonly used classifications for permafrost on land: continuous (underlying 90-100% of the landscape), discontinuous (underlying 50-90% of the landscape), and sporadic (underlying 0-50% of the landscape). Undersea permafrost is in a separate category, and is only found in the Arctic Ocean. A 2008 study by T. Zhang, et. al. titled "Statistics and characteristics of permafrost and ground-ice distribution in the Northern Hemisphere" found that permafrost covers an area of approximately 24% of the exposed land in the northern hemisphere.
Permafrost is responsible for Alaska being a carbon sink - but as it melts, it has the potential to significantly speed up the process of climate change and turn Alaska into a carbon source. There is an incredible amount of carbon stored in the organic matter of plants and animals frozen in permafrost. As permafrost thaws, that organic matter begins to decay and gets eaten and digested by microbes. The bacteria then produce carbon dioxide as a waste product, or methane as waste if the digestion took place in an anaerobic environment.
It is difficult to know exactly how much carbon is stored in permafrost but current estimates put it between 1,400 to 1,850 gigatons of carbon (NASA). To put this in context, 350.org estimates that if we want to keep global warming below 2 degrees Celsius then we can only release 565 gigatons more of carbon dioxide into the atmosphere.
Thawing permafrost is not an abstract concern for everyone on the planet. Some communities, such as the town of Bethel, Alaska, are already being affected. Permafrost has been a stable part of the landscape for hundreds of years and it supports infrastructure in many areas. Bethel has historically dealt with a small amount of seasonal freeze and thaw of permafrost, but this thaw is different. In Bethel river banks have experienced increased erosion, homes have sunk unevenly into the ground, roads have warped, and trees stand at a slant because the earth is literally moving beneath them.
One of the biggest casualties of the melting permafrost is Bethel's busiest road, Chief Eddie Hoffman Highway. It has become so riddled with bumps and dips that a recent Department of Transportation review estimated that it would cost about nine million dollars to repair. Department of Transportation officials believe that culverts that trap air under the roadway, and the six inch base of insulating foam asphalt under the roadway are mainly to blame for hastening the thaw of the permafrost under the road. Unfortunately, there are no current better plans for paving the road. Gravel would likely have less of a thawing affect on the permafrost, and is more easily evened out, but would require more daily and seasonal maintenance than asphalt. For now, Bethel is doing the best they can with as-needed repairs and hoping for a better long term solution to come along.