Permafrost is permanently frozen ground that remains at or below 0ºC (32ºF) for at least two years and can range from 1 – 1,000 meters in depth. It is found in Greenland, Alaska, Russia, China and Eastern Europe and covers approximately 22.8 million square kilometers (8.8 million square miles). That’s about 24% of the land surface of the Northern Hemisphere.
Thawing of permafrost
Permafrost represents one of the largest natural reserves of organic carbon in the world. Recent work and model projections on the effect of soil warming indicate that the carbon in permafrost soil will be increasingly vulnerable to decomposition into the greenhouse gases carbon dioxide and methane. This would result in a positive feedback mechanism amplifying further warming.
A gradual thawing of the permafrost is currently taking place. The upper layer of soil that is seasonally thawed is getting thicker. Once thawed, soil microorganisms convert the carbon into carbon dioxide and methane (21 times more effective as a greenhouse gas than carbon dioxide). This process is already incorporated into many climate models. It has been generally thought to have minimal effect as the warming also stimulates the growth of plants. This counterbalance the carbon release by utilizing the carbon dioxide in photosynthesis (the process by which plants and algae convert solar energy into chemical energy).
The results of a 7-year laboratory study on thawing permafrost were published in Nature Climate Change in March of this year. The researchers had to wait for 3 years before the bacteria capable of producing methane were present to produce detectable levels. The team also found that in the absence of oxygen, equal amounts of carbon dioxide and methane are produced. This means that methane production by this process can have a significant effect on the climate.
Their calculations also show that the permafrosts of Northern Europe, Northern Asia and North America could produce 1 gigaton (1×109 tonnes) of methane and 37 gigatons of carbon dioxide by 2100, but with uncertainties depending on whether the soils are wet or dry. NASA has carried out extensive studies on permafrost and the nature and implications of its thawing in terms of the release of methane.
Abrupt thawing of permafrost
One new concern is the concept of ‘abrupt thawing’, a process that can take place under a type of Artic lake, called a thermokarst lake, that forms as permafrost thaws. The implications of abrupt thawing would be the release of permafrost-derived methane and carbon dioxide into the atmosphere.
A study published in Nature Communications in August this year looked at the implications of abrupt thawing in detail. The study indicated that an abrupt thaw accelerates the mobilisation of carbon in the permafrost by 125-190% compared to gradual thaw alone. The authors recommend that these results should be incorporated into system models to give a more meaningful projection. The time scale for this problem having a significant effect is thought to be measured in decades and not centuries. Even if humans reduced their global carbon emissions, large releases of methane from abrupt thawing would still take place.
Nitrous oxide and permafrost
Methane and carbon dioxide are not the only greenhouse gases released during the thawing of permafrost. A 2017 study looked at the nitrogen content in permafrost and estimated it to be more than 67 billion tons. Bacteria in thawing permafrost can produce nitrous oxide, a gas more than 300 times more effective as a greenhouse gas than carbon dioxide. The nitrous oxide problem has attracted much less attention that the generation of carbon dioxide and methane. This study suggests that thawing permafrost may produce substantial amount of nitrous oxide over almost 25% of the entire Arctic.
Thawing permafrost is clearly seen as a major player in climate change.