Today being a holiday, I am only going to publish one story, and it is not even a brand new story. This was created by the New York Times back on August 23, and I managed to overlook it at the time. It is actually among the clearest and most informative that have ever graced these letters, so I recommend that you give it an extra bit of concentrated reading time. It so happens that lately I have been spending extra time studying the era known as the Pliocene, because of some questions that came up due to a news release. (See the “ice core” stories in letters # 982 and 984.) The CO2 level did in fact fall sharply to around 300 ppm just before the time of the core dating. Other than that, the research made me want to learn everything there is to know about the Pliocene era, which features the formation of both glaciers and the closely associated permafrost, and how these phenomena fit into our understanding of climate history and the current problem we call climate change. This Times story very accurately describes a number of important points that are also available in current scientific studies. I will highlight three of them below, with my own comments added.
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“Worldwide, permafrost is thought to contain about twice as much carbon as is currently in the atmosphere.” Ordinary soil is not nearly that carbon-rich. Most of the extra amount had to accumulate during the process of permafrost formation, which did not begin in the Northern Hemisphere until late in the Miocene, or shortly before the Pliocene, about 6-7 million years ago. The ongoing transfer of CO2 to a growing permafrost base, irregular as it was, enabled a long-term trend of planetary cooling, augmented by the growth of glaciers and their strong albedo effect.
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“Starting just a few feet below the surface and extending tens or even hundreds of feet down, it contains vast amounts of carbon in organic matter — plants that took carbon dioxide from the atmosphere centuries ago, died and froze before they could decompose.” This is a good description of the way carbon can accumulate in soil that is gradually turning to permafrost over a number of shorter and shorter growing seasons.
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” Scientists have estimated that the process of permafrost thawing could contribute as much as 1.7 degrees Fahrenheit to global warming over the next several centuries, independent of what society does to reduce emissions from burning fossil fuels and other activities.” That’s the real bell-ringer. 1.7F is about the same as 1.0C. Observe that this is out of our control. It will be independently added on to whatever short-term target we achieve by way of the Paris agreement, and does not necessarily close out the story of how much greenhouse gas and higher temperature the now unstoppable permafrost meltdown can ultimately produce.
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In short, permafrost formation, unlike rock weathering to eventually become limestone, is an extremely efficient way to remove CO2 from the atmosphere, using plants as intermediaries, and lock it up, but in this case the method of lockup is not permanent. If the permafrost is all allowed to melt then all the carbon that was put away will ultimately come bouncing back. Meanwhile the human emissions caused by burning fossil fuels, that were once more tightly locked up, are not about to go away. The challenge that lies ahead for negative emissions technology is indeed not a small one.
Carl