Whatever happened to the estimate that 51% of all human-caused greenhouse gas emissions are from livestock agriculture (“Livestock and Climate Change,” Robert Goodland and Jeff Anhang, WorldWatch, Nov.-Dec. 2009)? This certainly supports the vegan cause, but is it scientifically valid?
This claim revolves around how much of an impact human land use has on the carbon cycle. What difference would it make if we didn’t have any livestock industry today? The areas now used to graze livestock, or grow crops for livestock, would revert to their natural vegetation, which in many cases would be forest areas. A new article published earlier this month in Science now gives us a better idea of the potential of reforestation. Even excluding existing forests, urban areas, and farm areas(!), reforestation could store around 200 gigatons of carbon, which is about two-thirds of the carbon humans have put into the atmosphere since the industrial revolution, and thus getting rid of 25% of the CO2 currently in the atmosphere. This would reduce the CO2 levels from the June 2019 estimate of 414 ppm to 310 ppm, way beyond the most optimistic scenarios of 350.org. While this doesn’t explicitly address livestock agriculture, it’s clearly relevant, since most deforestation these days is linked to clearing forest land for livestock grazing or livestock feed crops.
The authors provided a video explaining this study that includes an interview with the lead author of the study, Dr. Jean-Francois Bastin. They conclude: “That makes forest restoration by far the biggest climate change solution that we have today.”
Some people immediately questioned the study. One scientist did not dispute the conclusion, but its relevance; the true impact of such a program would be more like 100 gigatons of carbon removed, not 200 gigatons, because much of this absorbed carbon would be absorbed anyway by the soil and the oceans. Even if this objection is allowed, we would not want the oceans to absorb any more CO2, because of ocean acidification. The impact would still be significant; this would mean that such reforestation would “only” reduce CO2 levels by a mere 12.5%, or to 362 ppm — still most of the way to the fabled target of 350 ppm.
And what is even more amazing, this study didn’t even include any farmland, much of which is being used for livestock. If this is the case, the effect of returning all land devoted to livestock to its natural vegetation would be even greater. The Goodland /Anhang figure of 51% from livestock would not be too radical, but much too conservative. But the Bastin, et al. article is still broadly in line with Goodland and Anhang’s article, because it postulated a similar mechanism.
It also broadly agrees with the earlier estimate of Sailesh Rao and his colleagues, who estimated that abandoning all livestock agriculture would take about 265 gigatons of carbon out of the atmosphere due to revegetation. Whereas this latest study by Bastin et al. found 0.9 billion hectares available outside of urban and agricultural areas, Rao et al. found 1.96 billion hectares available if we ditched livestock agriculture altogether. Finally, it also supports William Ruddiman’s estimate (in Plows, Plagues, and Petroleum) that even before the industrial revolution, with human population less than 10% of today’s population and an agriculture to match, land use changes had already raised atmospheric levels by about 40 ppm of CO2.
In short, there is converging evidence from several different directions that lead to the conclusion that land use is a critical element in fighting climate change.
But we don’t have an unlimited amount of time to do this. We are perilously close to critical climate tipping points, if we have not already exceeded them, and we’re progressively destroying the land that could grow these forests. Professor Tom Crowther, a senior author of the Bastin et al. study, said “it will take decades for new forests to mature and achieve this potential. It is vitally important that we protect the forests that exist today, pursue other climate solutions, and continue to phase out fossil fuels from our economies in order to avoid dangerous climate change.”
We certainly need to phase out the use of fossil fuels as well; besides their climate effects, they are finite in quantity and we’re close to (if not beyond) the peak of world oil production. But the key take-away from this is that scientists, activists, and the public ought to be heeding the message that changing the way that we use land is absolutely essential in dealing with climate change.
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Full citation of the referenced article: “The global tree restoration potential.” Jean-Francois Bastin, Yelena Finegold, Claude Garcia, Danilo Mollicone, Marcelo Rezende, Devin Routh Constantin M. Zohner, Thomas W. Crowther. Science, 05 Jul 2019:Vol. 365, Issue 6448, pp. 76-79, DOI: 10.1126/science.aax0848.