Person: Butler, Ethan E.
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Butler
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Ethan E.
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Butler, Ethan E.
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Publication Cooling of US Midwest summer temperature extremes from cropland intensification(Nature Publishing Group, 2015) Mueller, Nathaniel; Butler, Ethan E.; McKinnon, Karen Aline; Rhines, Andrew Nelson; Tingley, Martin; Holbrook, Noel; Huybers, PeterHigh temperature extremes during the growing season can reduce agricultural production. At the same time, agricultural practices can modify temperatures by altering the surface energy budget. Here we identify centennial trends towards more favourable growing conditions in the US Midwest, including cooler summer temperature extremes and increased precipitation, and investigate the origins of these shifts. Statistically significant correspondence is found between the cooling pattern and trends in cropland intensification, as well as with trends towards greater irrigated land over a small subset of the domain. Land conversion to cropland, often considered an important influence on historical temperatures, is not significantly associated with cooling. We suggest that agricultural intensification increases the potential for evapotranspiration, leading to cooler temperatures and contributing to increased precipitation. The tendency for greater evapotranspiration on hotter days is consistent with our finding that cooling trends are greatest for the highest temperature percentiles. Temperatures over rainfed croplands show no cooling trend during drought conditions, consistent with evapotranspiration requiring adequate soil moisture, and implying that modern drought events feature greater warming as baseline cooler temperatures revert to historically high extremes.Publication Variations in the sensitivity of US maize yield to extreme temperatures by region and growth phase(IOP Publishing, 2015) Butler, Ethan E.; Huybers, PeterMaize yield is sensitive to high temperatures, and most large scale analyses have used a single, fixed sensitivity to represent this vulnerability over the course of a growing season. Field scale studies, in contrast, highlight how temperature sensitivity varies over the course of development. Here we couple United States Department of Agriculture yield and development data from 1981–2012 with weather station data to resolve temperature sensitivity according to both region and growth interval. On average, temperature sensitivity peaks during silking and grain filling, but there are major regional variations. In Northern states grain filling phases are shorter when temperatures are higher, whereas Southern states show little yield sensitivity and have longer grain filling phases during hotter seasons. This pattern of grain filling sensitivity and duration accords with the whole-season temperature sensitivity in US maize identified in recent studies. Further exploration of grain filling duration and its response to high temperatures may be useful in determining the degree to which maize agriculture can be adapted to a hotter climate.Publication Adaptation of US maize to temperature variations(Nature Publishing Group, 2013) Butler, Ethan E.; Huybers, PeterHigh temperatures are associated with reduced crop yields1, 2, and predictions for future warming3 have raised concerns regarding future productivity and food security4, 5, 6, 7, 8. However, the extent to which adaptation can mitigate such heat-related losses remains unclear9, 10, 11, 12, 13. Here we empirically demonstrate how maize is locally adapted to hot temperatures across US counties. Using this spatial adaptation as a surrogate for future adaptation, we find that losses to average US maize yields from a 2 °C warming would be reduced from 14% to only 6% and that loss in net production is wholly averted. This result does not account for possible changes in temperature variability or water resources, nor does it account for all possible forms of adaptation14, 15, 16, 17, 18, but it does show that adaptation is of first-order importance for predicting future changes in yield. Further research should be undertaken regarding the ability to adapt to a changing climate, including analysis of other crops and regions, the application of more sophisticated models of crop development, and field trials employing artificially increased temperature.Publication American Maize: Climate Change, Adaptation, and Spatio-Temporal Variation in Temperature Sensitivity(2015-04-20) Butler, Ethan E.; Huybers, Peter; Holbrook, N. M.; Mitrovica, Jerry; Schrag, Daniel; Wofsy, StevenAgricultural production is vulnerable to climate change. However, this vulnerability can be reduced by adapting food crops to a hotter climate. Many studies have ignored adaptation when quantifying the effect of climate change on crop yield, which has likely overestimated yield losses. Therefore, it is necessary to quantify agriculture's adaptive potential to climate change. Such work is challenging because there are no historical analogues to current or future warming. In place of such a precedent this work explores the varying sensitivity of maize yield to elevated temperatures through a suite of multiple linear regression models. These models use high resolution yield and crop development data available since 1981 in the United States to account for overlooked features of maize physiology and agricultural management. The results of these models substantially alter estimates of how crops will respond to a warming environment. The studies here illustrate how finer scale details can be incorporated into broader regional models. Temperature sensitivity is found to vary with local climatology indicating that maize cultivars are adapted to their particular environment. Incorporating this historical adaptation into estimates of yield loss substantially reduces the effect of a modest warming. A physiological basis for spatial adaptation is apparent when maize development data are incorporated into the model -- cooler regions accelerate through sensitive development phases faster than hotter areas. The development data also suggest that crop development has been adapted to the seasonal cycle and that a non-trivial portion of the temporal trend in maize yield has resulted from management adjustments. Finally, the importance of spatio-temporal variation in temperature sensitivity is highlighted through case studies of recent years with record-setting yield losses. Spatial and/or temporal variation in temperature sensitivity is necessary to reduce bias in estimates of yield loss in these years. This work builds from previous conclusions regarding the negative effects of hot temperatures, and suggests that while hotter temperatures will harm maize yields there are steps that farmers might take to manage and reduce these losses. Taken together these results quantify how extant adaptation may help to ameliorate yield losses in a hotter future.