We’ve all heard that our houseplants grow better when we talk to them—but it’s not because they enjoy our company. They grow better because we breathe more carbon dioxide upon their leaves, which stimulates photosynthesis.

It’s a fact that plants and trees experience more rapid growth under elevated atmospheric carbon dioxide levels. Thus, lay people and scientists alike speculate that rising carbon dioxide levels due to human activity might not be the global catastrophe many climatologists and politicians have made it out to be. Apparently, the carbon produced via fossil fuel usage is being removed from the atmosphere, at least in part, by the extra growth occurring in plants and trees. That extra growth means we have more grain, fruit, nuts, seeds, and lumber. Given these substantial benefits, perhaps a little extra global warming from elevated atmospheric carbon dioxide levels is an acceptable tradeoff.

As is almost always the case with tradeoffs, it is easy to focus on one tradeoff and ignore others and bring upon ourselves unintended consequences. In a recent Today’s New Reason to Believe article, I addressed such an additional tradeoff in a more elevated atmospheric carbon dioxide scenario. A team of 20 ecologists and earth system scientists published a paper in Nature wherein they reveal and measure yet another tradeoff under elevated atmospheric carbon dioxide conditions.1  

This team first pointed out previous research showing that terrestrial vegetation removes only about 30 percent of the carbon dioxide emitted by human activities.2 They also cited elevated carbon dioxide experiments performed on plants showing that while plant biomass often increases,3 the organic carbon stored in accompanying soils may slightly increase, remain the same, or decrease.4

In an effort to resolve the ambiguity in what happens to soil organic carbon (SOC), the 20 researchers synthesized data from 108 elevated carbon dioxide experiments. These experiments included both grasslands and forests in various sites in North and South America, Africa, Australia, Europe, and Asia.

The synthesized data revealed that when plant biomass is strongly enhanced by elevated atmospheric carbon dioxide, SOC storage declines. When plant biomass is only weakly enhanced, SOC storage slightly increases. The team of 20 determined that plant nutrient acquisition explains the tradeoffs they observed. Plants that significantly augment their biomass mine their soils for nutrients, which decreases SOC storage.

The researchers noted a consistent difference between grasslands and forests. SOC storage increases with elevated atmospheric carbon dioxide in grasslands, but not in forests. The results of the synthesized data reveal the potential of grassland soils to store carbon as atmospheric carbon dioxide levels continue to rise. The team cautions, however, that in developing climate models under increasing atmospheric carbon dioxide scenarios it is easy to overestimate plant carbon and SOC storage potentials. All climate models show that the potential of vegetation to take up atmospheric carbon dioxide will slow later in the 21st century owing to nutrient constraints.5 In my Today’s New Reason to Believe article I showed that increasing global mean temperatures establish an even more severe constraint.

Thanks to research efforts of the 20 ecologists and earth system scientists, we have a superior blueprint for managing forest and grassland ecosystems in the context of increasing atmospheric carbon dioxide levels. The team also has laid an important foundation for the development of more detailed and reliable climate models. The world’s peoples and nations now possess even greater motivation to limit—in economically beneficial ways—further increases in atmospheric greenhouse gases. As the author of Weathering Climate Change, I am pleased that these 20 researchers have affirmed my thesis that there are ways forward where we can stabilize the global climate while we simultaneously benefit human economy and the world’s ecosystems. We really can fulfill the mandate God gave us in Genesis 1 to manage Earth’s resources for our benefit and the benefit of all life.

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Endnotes

1. César Terrer et al., “A Trade-Off between Plant and Soil Carbon Storage Under Elevated CO2,” Nature 591, no. 7851 (March 25, 2021): 599–603, doi:10.1038/s41586-021-03306-8.
2. Pierre Friedlingstein et al., “Global Carbon Budget 2020,” Earth System Science Data 12, no. 4 (December 2020): 3269–3340, doi:10.5194/essd-12-3269-2020.
3. Sofia Baig et al., “Does the Growth Response of Woody Plants to Elevated CO2 Increase with Temperature? A Model-Oriented Meta-Analysis,” Global Change Biology 21, no. 12 (December 2015): 4303–4319, doi:10.1111/gcb.12962; Richard J. Norby et al., “Forest Response to Elevated CO2 Is Conserved across a Broad Range of Productivity,” Proceedings of the National Academy of Sciences USA 102, no. 50 (December 13, 2005): 18052–18056, doi:10.1073/pnas.0509478102.
4. Kees Jan van Groenigen et al., “Faster Decomposition Under Increased Atmospheric CO2 Limits Carbon Storage,” Science 344, no. 6183 (May 2, 2014): 508–509, doi:10.1126/science.1249534.
5. César Terrer et al., “Nitrogen and Phosphorus Constrain the CO2 Fertilization of Global Plant Biomass,” Nature Climate Change 9, no. 9 (September 2019): 684–689, doi:10.1038/s41558-019-0545-2; Peter B. Reich, Bruce A. Hungate, and Yiqi Luo, “Carbon-Nitrogen Interactions in Terrestrial Ecosystems in Response to Rising Atmospheric Carbon Dioxide,” Annual Review of Ecology, Evolution, and Systematics 37 (December 12, 2006): 611–636, doi:10.1146/annurev.ecolsys.37.091305.110039; Richard J. Norby et al, “CO2 Enhancement of Forest Productivity Constrained by Limited Nitrogen Availability,” Proceedings of the National Academy of Sciences USA 107, no. 45 (November 9, 2010): 19368–19373, doi:10.1073/pnas.1006463107.