Thread by @bdowduribe

@TedNordhaus asserts that “a federal climate effort [must] take agriculture seriously…, including [GM] crops.” This positive take on GMOs as a US climate solution rests on assumptions that are not well supported by the science THREAD #ClimateAction #ClimateCrisis #GMO #scicomm

https://twitter.com/danrejto/status/1362891460798935040

Nordhaus argues that GMOs boost yields, reducing land conversion to agriculture + therefore reducing GG emissions. The problem is that there is no scientific consensus on GM crops boosting yields, nor is the science clear that yield increases lead to land not being used for ag 1/

If a GM yield effect does exist, it is difficult to establish the difference it makes from on-going yield trends. Research by @Jack_Heinemann shows that cereal yield increases in Europe + US were the same despite the absence of GM crops in Europe 2/ tandfonline.com/doi/full/10.10…

The 2009 report, A Failure to Yield, by the Union of Concerned Scientists also shows that GM corn and soy have not increased yields in the US 3/ ucsusa.org/sites/default/…

Before dismissing these analyses by pointing to other studies which do show a GM crop yield increase, note that it is very difficult to establish a yield effect of the GM trait and distinguish it from other factors involved in agricultural production 4/ academia.edu/2167700/Constr…

The 2016 Academy of Sciences GM crop report said as much: “The nation-wide data on maize, cotton, or soybean in the US do not show a significant signature of GM technology on the rate of yield increase” 5/ nationalacademies.org/our-work/genet…

Indeed, a recent analysis by @glenndavisstone in India shows that GM cotton yield increases are more likely attributed to increased fertilizer use. Previous analyses had attributed these modest yield gains to the GM trait 6/ nature.com/articles/s4147…

The GM crop literature also fails to compare them against other ways to boost yields. The focus should be on the best interventions which meet multiple socially-important goals. W/out such comparisons, the risk is supporting any yield boosting strategy rather than the best one 7/

Even more problematic than yields is the assumption that if farmer A increases yields, farmer B will decrease her land use or land will be spared elsewhere from being converted for ag. This process known as “land sparing” is not well supported in the scientific literature 8/

If a scientific consensus exists on this issue it is best summed up by this 2009 paper, which states that when ag yields go up “land-sparing is a weak process that occurs under a limited set of circumstances.” 9/ onlinelibrary.wiley.com/doi/pdf/10.111…

For developed counties like the US - the subject of the @TedNordhaus opinion piece - the same paper is unequivocal: “In developed countries, there was no evidence that higher staple crop yields were associated with decreases in per capita cropland area.” 10/

In sum, to champion GM crops as a US climate solution you must believe that they (a) boost yields (not well supported; maybe marginally), (b) cancel land conversions elsewhere (not likely), and (c) are better than other approaches on these metrics (not likely). 11/

It is important that science be a leader in setting climate policy. In this case, the science doesn’t support strong advocacy for GM crops as a US climate solution. FIN