Background
The authors write that "high temperatures are associated with reduced crop yields, and predictions for future warming have raised concerns regarding future productivity and food security." More specifically, they note that "global maize yields are forecast to decline in response to increasing temperature, particularly as the upper range of growing season temperatures becomes hotter," citing Schlenker and Roberts (2006), Easterling et al. (2007), Lobell and Field (2007), Battisti (2009), Lobell et al. (2011) and Roberts and Schlenker (2011). However, they caution that "the extent to which adaptation can mitigate such heat-related losses remains unclear," and they thus proceed to present some much-needed clarity on this subject.

What was done
Butler and Huybers empirically demonstrated how maize is locally adapted to hot temperatures across a subset of 1,013 US counties, after which they used this spatial adaptation "as a surrogate for future adaptation," noting that "US corn hybrids have a product half-life of about 4 years, suggesting sufficiently rapid turnover to adapt to decadal changes in climate."

What was learned
With the help of this adaptation phenomenon, the two researchers determined that (1) "losses to average US maize yields from a 2°C warming would be reduced from 14% to only 6%," and that (2) "loss in net production is wholly averted." As for a few specifics on the matter, they indicate that under the 2°C warming scenario, "Minnesota stands to increase yields by 11%; the yield losses from northern Ohio west to northern Missouri are nearly eliminated; and North Carolina, Georgia and east Texas reduce losses from 49% without adaptation to 39% with it."

What it means
In the concluding paragraph of their report, Butler and Huybers write that "losses to US maize yield from increased temperature," such as those suggested by Schlenker and Roberts (2006, 2009), "are almost certainly overestimated if adaptation is not accounted for." But if it is a part of the analysis, their work suggests that there could well be no net loss in productivity across the entire corn-production region.

References
Battisti, D.S. and Naylor, R.L. 2009. Historical warnings of future food insecurity with unprecedented seasonal heat. Science 323: 240-244.

Easterling, W., Aggarwal, P., Batima, P., Brander, K., Erda, L., Howden, M., Kirilenko, A., Morton, J., Soussana, J.-F., Schmidhuber, S. and Tubiello, F. 2007. Food, fibre and forest products. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. and Hanson, C.E. (Eds.). Cambridge University Press, Cambridge, United Kingdom, pp. 273-313.

Lobell, D.B., Banziger, M., Magorokosho, C. and Vivek, B. 2011. Nonlinear heat effects on African maize as evidenced by historical yield trials. Nature Climate Change 1: 42-45.

Lobell, D.B. and Field, C.B. 2007. Global scale climate-crop yield relationships and the impacts of recent warming. Environmental Research Letters 2: 10.1088/1748-9326/2/1/014002.

Roberts, M. and Schlenker, W. 2011. In: Libecap, G. and Steckel, R. (Eds.) The Economics of Climate Change, Adaptations Past and Present. University of Chicago Press, Chicago, Illinois, USA, pp. 225-252.

Schlenker, W. and Roberts, M.J. 2006. Nonlinear effects of weather on corn yields. Review of Agricultural Economics 28: 391-398.

Schlenker, W. and Roberts, M.J. 2009. Nonlinear temperature effects indicate severe damage to U.S. crop yields under climate change. Proceedings of the National Academies of Science USA 106: 15,594-15,598.