Study: Earth's Plants And Soils' Ability To Absorb CO2 Has Been Declining Since 2008, Averaging .25% Per Year
Our planet is losing its appetite for mopping up carbon dioxide. Analysis of atmospheric carbon dioxide measurements show that Earth’s plants and soils reached peak carbon dioxide sequestration in 2008 and absorption has been declining ever since. Passing this tipping point increases the chances of runaway climate breakdown.
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James Curran, the former chief executive of the Scottish Environment Protection Agency, and his son Sam analysed the ups and downs in atmospheric carbon dioxide concentration, revealing that peak carbon sequestration occurred in 2008, and since then the amount of carbon dioxide absorbed by plants has declined by an average of 0.25% a year. “The findings are very stark. Emissions now need to fall by 0.3% per year, just to stand still. That’s a tall order since they typically increase by 1.2% per year,” said James Curran, whose findings are published in the journal Weather.
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Abstract
The rate of natural sequestration of CO2 from the atmosphere by the terrestrial biosphere peaked in 2008. Atmospheric concentrations will rise more rapidly than previously, in proportion to annual CO2 emissions, as natural sequestration is now declining by 0.25% per year. The current atmospheric increment of +2.5ppm CO2 per year would have been +1.9ppm CO2, if the biosphere had maintained its 1960s growth rate. This effect will accelerate climate change and emphasises the close connection between the climate and nature emergencies. Effort is urgently required to rebuild global biodiversity and to recover its ecosystem services, including natural sequestration.
Introduction
Two earlier Weather papers (Curran and Curran, 2016a,b) analysed the well-known Keeling Curve for evidence of the impact of natural carbon sequestration on the progress of climate change. Almost 10 years later, it seems an appropriate time to extend the analysis and verify, or otherwise, the earlier findings.
Previous analysis
Figure 1 illustrates a typical excerpt from the Keeling Curve over slightly more than 1 year. Overall, the concentration of CO2 in the atmosphere, as recorded at the Mauna Loa Observatory in Hawaii, is increasing – but the very noticeable intra-annual dip, with a minimum in the Northern Hemisphere autumn, is the result of the huge uptake of CO2 from the atmosphere by vegetation across the extensive Northern Hemisphere land mass during its summer. This uptake is known as natural sequestration, and its magnitude is directly related to the health of the global biosphere. A proportion of this absorbed CO2 is released back into the atmosphere during the winter period, due to natural biodegradation of dead vegetation, but some remains locked up in roots, soils and dormant woody growth. Of course, in the meantime, anthropogenic global CO2 emissions continue to further augment the atmospheric concentration, so there is a net increase. It should be noted that the seasonal variation of CO2 generated by the much smaller Southern Hemisphere land mass is very weak, and that the global oceans provide a rather steady sequestration of CO2 (Jiang and Yung, 2019).
New and extended analysis
Analysis of the data underlying the Keeling Curve (Keeling and Graven, 2021) is fully explained in Curran and Curran (2016a). Here, the calculation is replicated but with the substitution of new data for the most recent 10 years, up to the CO2 atmospheric maximum in 2024. In summary, and as shown in Figure 1, a quadratic regression is fitted through the time series maxima (for which y = 0.0132x2 + 0.7485x + 316.94 with R2 = 0.9994) and minima (for which y = 0.0136x2 + 0.7073x + 311.09 with R2 = 0.9994) of the Keeling Curve, derived from published weekly averages (Lan, 2024). The parameter d, in Figure 1, is evaluated for each year by taking the difference between the two regression lines. The results for the magnitude of this intra-annual drop, by year, are presented in Figure 2.
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https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.7668