You can think of the Arctic permafrost as a giant kitchen freezer. If you put organic matter in your freezer, the food will stay intact. But if the freezer compressor breaks, it will slowly heat up. As it heats up, bacteria begin to eat your food. The bacteria make the food go rotten. And as the bacteria consume the food, they produce carbon dioxide, methane, and other gases and chemicals that smell terrible.
For tens of thousands of years, permafrost has acted like a freezer, keeping 1,400- to 1,600 gigatons (billion tons) of plant matter carbon trapped in the soil. That’s more than double the amount of carbon currently in the atmosphere. Plants are growing in permafrost regions, and when those plants die, because of the cold temperature, they don't fully decompose, so some of that organic carbon is left behind. When the permafrost thaws, it starts to rot, it starts to decompose, and that's what's releasing carbon dioxide and methane. This is one reason scientists are so worried about a melting Arctic – When the bacteria turn the carbon in the Arctic into C02 and methane, it accelerates a feedback loop. The more methane and carbon released, the more warming. A 2014 study in Environmental Research Letters estimates that thawing permafrost could release around 120 gigatons of carbon into the atmosphere by 2100, resulting in 0.29°C of additional warming. By 2300, another study in Nature Geoscience concludes, the melting permafrost and its resulting carbon feedback loops could contribute to as high as 1.69°C of warming.
But these are just estimates, and they come with a good deal of uncertainty. It all depends on how quickly the Arctic warms. The logic here is simple – the more warming, the greater the risk of kick-starting this feedback loop. And carbon isn’t the only pollutant trapped in the ice. A new study in Geophysical Research Letters finds that the Arctic permafrost is the largest repository of mercury on Earth. Mercury is a potent neurotoxin. And scientists now think there is around 15 million gallons frozen in permafrost soils — nearly twice the amount of mercury found in all other soil, the ocean, and atmosphere combined. The release of heavy metals, particularly mercury, and other legacy contaminants currently stored in glaciers and permafrost, is projected to reduce water quality for freshwater biota, household use and irrigation,” the IPCC reports. Scientists don’t know how much of this mercury could be released, or when. But they do know this – continued melting will make it more likely for the mercury to be released, pollute the ocean, and accumulate in the food chain.
This is the second part of a 5 episode series on climate change and new diseases. You can check them all out using this link.