My last post discussed some recent research we conducted on the impacts of biotechnology adoption on corn yields. A reader forwarded a link to a recent paper in the journal Nature Climate Change raising an issue I hadn't yet heard about. Using some simulations, the authors argue that increased solar radiation, which led to brighter skies, has had a big impact on recent increases in corn yields.
Here's the abstract:
“Predictions of crop yield under future climate change are predicated on historical yield trends, hence it is important to identify the contributors to historical yield gains and their potential for continued increase. The large gains in maize yield in the US Corn Belt have been attributed to agricultural technologies, ignoring the potential contribution of solar brightening (decadal-scale increases in incident solar radiation) reported for much of the globe since the mid-1980s. In this study, using a novel biophysical/empirical approach, we show that solar brightening contributed approximately 27% of the US Corn Belt yield trend from 1984 to 2013. Accumulated solar brightening during the post-flowering phase of development of maize increased during the past three decades, causing the yield increase that previously had been attributed to agricultural technology. Several factors are believed to cause solar brightening, but their relative importance and future outlook are unknown, making prediction of continued solar brightening and its future contribution to yield gain uncertain. Consequently, results of this study call into question the implicit use of historical yield trends in predicting yields under future climate change scenarios.”
I don't know enough about the issue to speak to the credibility of the authors' findings. However, I not sure that this is much of a confound for our study on biotech adoption because our estimated effects are (partially) identified by using variation in yields across states that have differential adoption rates (and yet are presumably exposed to the same solar radiation). To the extent that identification our effects of biotech adoption come about from comparisons of yields in the same counties over time (where solar radiation varied over time), this could be an issue, but again, the time trend included in our models should pick up this effect as well.