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

Revised Estimates on Methane Levels in The Atmosphere

As the Earth’s atmosphere and oceans warm up, theoretical models suggest that this is due to the effects of increased levels of various gasses, including CO2 and Methane (CH4).  But where are those gasses coming from, exactly?

In the case of Methane in the atmosphere, there are many sources, including human agriculture (livestock), fossil fuel use (oil, coal, gas), natural sources such as wetlands, as well as changes in chemical sinks that absorb Methane.  Uncertainties about the sources of Methane mean that projections of future growth are imprecise.

Global levels and isotopic composition of CH4 are measured by satellites, as are other atmospheric chemicals.  Satellites also measure vegetation growth on land and sea and large fires.  Wild fires release Methane and other gasses, so increases in the frequency or duration of fires is one possible source of increased Methane.

Puruseing an accurate assessment of this question, John R. Worden and colleagues report on efforts to improve the understanding of the total amount of biomass burning and the amount of Methane contributed [2], This is a complicated problem because fires are sporadic and irregular, and the effects are not necessarily easy to measure (e.g., to estimate how much and what kind of vegetation burned).

Their excellent study uses multiple data sources.

“we combine bottom-up esti- mates of fire emissions, based on burnt area measurements, with the top-down CO emissions estimates…, based on the satellite concentration data” ([2], p. 2)

This is a very tricky bit of work, which has to take into consideration the details and error ranges of the different data sources it combines.

The overall results show that emissions from burning biomass were lower than previous estimates based on burned area. This brings the estimate into agreement with measures of atmospheric gasses. The finding that the atmospheric isotope studies accurately estimate emissions from burning biomass suggests that the increases in fossil fuel emissions from those same studies are accurate as well.

Overall, the study shows that the area of burned vegetation is not necessarily a good measure of the amount of emissions.  Combining multiple satellite datasets showed that the relationship is non-linear. This makes sense: all vegetation is not the same, nor are all fires equivalent.

It is also important to note that emissions from burning biomass are not themselves particularly large, and in fact are smaller than previous estimates.  The important thing is that this study makes the data from all sources more consistent with each other, increasing confidence in the accuracy of the data and the theoretical models.

Nice work.

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1. Adam Voiland. 2018. “What is Behind Rising Levels of Methane in the Atmosphere?” NASA Earrth Observatory, January 11. https://earthobservatory.nasa.gov/IOTD/view.php?id=91564&src=eoa-iotd
2. John R. Worden, A. Anthony Bloom, Sudhanshu Pandey, Zhe Jiang, Helen M. Worden, Thomas W. Walker, Sander Houweling, and Thomas Röckmann. 2017. “Reduced biomass burning emissions reconcile conflicting estimates of the post-2006 atmospheric methane budget.” Nature Communications 8 (1):2227. doi: 10.1038/s41467-017-02246-0 https://doi.org/10.1038/s41467-017-02246-0.

 

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