An important study was published one year ago that I should have reviewed in these letters but somehow overlooked at the time. It dealt with a potential loss of a significant amount of the “carbon sink” that we depend on to hold down possible increases in the level of CO2 concentration in the atmosphere due to constantly rising emissions. Assuming that a number of readers have not become aware of this study elsewhere, today’s letter will be devoted to a makeup review, mostly dependent on outside sources of coverage. A good place to start is with an old reliable, Bob Berwyn, writing for Inside Climate News: https://insideclimatenews.org/news/13012021/forests-heat-climate-change/.
Another good source of introduction can be found at the Phys.org site: https://phys.org/news/2021-01-earth-temperature-years.html, and yet another from a site based in Australia: https://www.tern.org.au/ecosystem-tipping-points-carbon-sink-to-source-within-30-years/. Each of these adds more perspective to an issue that has many layers of possible actions that are interwoven and known to be mutually interdependent. The study itself, which has open access, does the best job of sorting these out, and is clearly written. I strongly suggest that you take the extra time needed to read it: https://www.science.org/doi/10.1126/sciadv.aay1052 The main conclusion, with my italics, is stated like this: “Given the temperature limits of land carbon uptake presented here, without mitigating warming, we will cross the temperature threshold of the most productive biomes by midcentury, after which the land sink will degrade to only ~50% of current capacity if adaptation does not occur.” (Some vegetation can move by itself or be transplanted, but most is considered unlikely to be able to adapt within such a short period of time.)
Currently in the early stages of degradation, the next 25 years are expected to see a steady trend of acceleration in losses of the land sink, assuming that temperatures are likely to remain on a rising track for a good many of those years. An actual reduction in the rate of CO2 emissions has yet to begin, and concentrations just keep growing. (See the chart and other data at https://gml.noaa.gov/ccgg/trends/graph.html.) This means we are already engaged in a race between the realization of annual emission reduction targets and any offsetting realization of natural losses of what has been a regular carbon sink provision.
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Not everyone accepts the conclusions of this study, and it should not be considered the last word on the subject, but neither can it be ignored. It could even prove to be overly conservative. This is a hot issue for researchers. Look for updates.
Carl