The Permafrost Is Outgassing

As the ice melts everywhere, the permafrost (permanently frozen soil) is also melting.  When this frozen muck thaws, it releases swamp gas—lots of CO2 and methane, for example—into the atmosphere.

Depending on the amount of freezing, thawing, and accumulation of seasonal debris (dead plants), the permafrost alternatively sucks in and puts out Carbon.

Since the last ice age, permafrost has generally remained frozen except for relatively shallow surface areas.  This has encapsulated the organic materials frozen there.  During the short summer, plants grow and absorb Carbon from the atmosphere, and the winter cold refrigerates the dead foliage, preventing decay back into the atmosphere.  So, up to now, permafrost has been a Carbon sink, soaking up Carbon out of the atmosphere .

As global air temperatures have risen, and polar surface areas even more rapidly warm, permafrost has begun to perma-melt.  Ultimately, this will tip the balance, so that the soil no longer retains additional Carbon.  Worse, the Carbon frozen underground over centuries will be released into the atmosphere [1].  This, like reduced albedo, is a potential positive feedback, speeding up warming.

However, data from these cold, remote regions is sparse, so it hasn’t been clear how much Carbon these regions absorb (in the summer) and emit (in the winter).  There are vast areas of permafrost in the Northern hemisphere, with a variety of vegetation, microbes, and seasonal patterns.

This winter, an international team reports on a comprehensive collection of measured CO2 emissions from northern permafrost.  They combine these measures with satellite observations of vegetation and conditions, and built a model of the physics.  This study indicates that CO2 emissions may already exceed uptake [2].

Source: NASA Earth Science News [3]

Extrapolating the model with different scenarios for global temperatures, the CO2 emissions could increase 17-41% by year 2100.  This would place it somewhere in the 1-2 billion tons or Carbon per year (compared to 30+ billion tons per year released due to human activities).  It looks like human generated warming has an additional side effect, causing tons of Carbon to be released from permafrost, which will only increase warming further.

Of course, these estimates are extrapolations from relatively sparse data points, and are aggregated over huge spaces and time periods.  (E.g., they estimate emissions for 25×25 km areas for a month.)  The study also neglects the “shoulder seasons” (spring and fall), and other gasses including methane.  Nevertheless, these results seem to be in line with data and theory, so they are plausible, as are the projections into the future.

The upshot is that the arctic is flipping from a Carbon sink to a Carbon source—pretty much the opposite of what we should want to see.

“The warmer it gets, the more carbon will be released into the atmosphere from the permafrost region, which will add to further warming,” said co-author and WHRC scientist Brendan Rogers. “It’s concerning that our study, which used many more observations than ever before, indicates a much stronger Arctic carbon source in the winter. We may be witnessing a transition from an annual Arctic carbon sink to a carbon source, which is not good news.” (From [3])

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1. John L. Campbell, Arctic loses carbon as winters wane. Nature Climate Change, 9 (11):806-807, 2019/11/01 2019. https://doi.org/10.1038/s41558-019-0604-8
2. Susan M. Natali, Jennifer D. Watts, Brendan M. Rogers, Stefano Potter, Sarah M. Ludwig, Anne-Katrin Selbmann, Patrick F. Sullivan, Benjamin W. Abbott, Kyle A. Arndt, Leah Birch, Mats P. Björkman, A. Anthony Bloom, Gerardo Celis, Torben R. Christensen, Casper T. Christiansen, Roisin Commane, Elisabeth J. Cooper, Patrick Crill, Claudia Czimczik, Sergey Davydov, Jinyang Du, Jocelyn E. Egan, Bo Elberling, Eugenie S. Euskirchen, Thomas Friborg, Hélène Genet, Mathias Göckede, Jordan P. Goodrich, Paul Grogan, Manuel Helbig, Elchin E. Jafarov, Julie D. Jastrow, Aram A. M. Kalhori, Yongwon Kim, John S. Kimball, Lars Kutzbach, Mark J. Lara, Klaus S. Larsen, Bang-Yong Lee, Zhihua Liu, Michael M. Loranty, Magnus Lund, Massimo Lupascu, Nima Madani, Avni Malhotra, Roser Matamala, Jack McFarland, A. David McGuire, Anders Michelsen, Christina Minions, Walter C. Oechel, David Olefeldt, Frans-Jan W. Parmentier, Norbert Pirk, Ben Poulter, William Quinton, Fereidoun Rezanezhad, David Risk, Torsten Sachs, Kevin Schaefer, Niels M. Schmidt, Edward A. G. Schuur, Philipp R. Semenchuk, Gaius Shaver, Oliver Sonnentag, Gregory Starr, Claire C. Treat, Mark P. Waldrop, Yihui Wang, Jeffrey Welker, Christian Wille, Xiaofeng Xu, Zhen Zhang, Qianlai Zhuang, and Donatella Zona, Large loss of CO2 in winter observed across the northern permafrost region. Nature Climate Change, 9 (11):852-857, 2019/11/01 2019. https://doi.org/10.1038/s41558-019-0592-8
3. Samson Reiny and Miles Grant, Permafrost Becoming a Carbon Source Instead of a Sink, in NASA Earth Science News. 2019. https://earthobservatory.nasa.gov/images/145880/permafrost-becoming-a-carbon-source-instead-of-a-sink