Understanding permafrost carbon and emissions

In the first video we watched for this course, we described permafrost as a large carbon reservoir.

Permafrost stores an estimated 1.4 trillion tonnes of carbon—almost double the amount already in the Earth’s atmosphere and three times more than has been released by humans through burning fossil fuels since the start of the industrial revolution—but where is this carbon?^[1]

Frozen soils also contain the frozen ancient remains of plants and animals. Often, these remains were partially decomposed before they were frozen, but whether or not you could recognize them as parts of plants or animals, they are still rich in carbon-dense organic matter. When the ground begins to thaw, those remains begin to thaw as well. As microorganisms decompose the newly-thawed organic matter, they can release carbon into the atmosphere in the form of the powerful greenhouse gasses carbon dioxide and methane.

Depending on how hot we let it get, carbon emissions from Arctic permafrost thaw are expected to be in the range of 30 to more than 150 billion tons of carbon (110 to more than 550 Gt CO2) this century, with upper estimates on par with the cumulative emissions from the entire United States at its current rate.^[2]

Potential cumulative permafrost carbon emissions (Gt CO2) by 2100 compared to some of the world’s largest fossil fuel emitting nations, if their current emissions rates continue through the end of the century. Neglecting permafrost is equivalent to excluding a major world economy from global climate policy. Data from Schuur et al. 2015, the Union of Concerned Scientists for 2019.

To cap warming at the internationally agreed-upon 2 degrees Celsius global temperature threshold established in the Paris Agreement (which you will learn more about later in this course), there is a limit—a budget—of how much more carbon can be added to the atmosphere. Permafrost thaw emissions could use up between 25 and 40% of that remaining carbon budget.

References

¹Schuur, E., McGuire, A., Schädel, C., Grosse, G., Harden, J., Hayes, D., et al., 2015. Climate change and the permafrost carbon feedback. Nature, 520(7546), pp.171-179.

²Natali, S., Holdren, J., Rogers, B., Treharne, R., Duffy, P., Pomerance, R. and MacDonald, E., 2021. Permafrost carbon feedbacks threaten global climate goals. Proceedings of the National Academy of Sciences, 118(21).