Miller Magazine Issue: 152 August 2022

62 COVER STORY MILLER / AUGUST 2022 part of the Agricultural Model Intercomparison and Improve- ment Project (AgMIP), an international partnership coordinated by Columbia University. The crop models simulate on a large scale how crops grow and respond to environmental condi- tions such as temperature, rainfall and atmospheric carbon di- oxide, which are provided by the climate models. Each crop species’ behavior is based on their real life biological respons- es studied in indoor and outdoor lab experiments. In the end, the team created about 240 global climate-crop model simula- tions for each crop. By using multiple climate and crop models in various combinations, the researchers were more confident in their results. “What we're doing is driving crop simulations that are ef- fectively growing virtual crops day-by-day, powered by a su- percomputer, and then looking at the year-by-year and de- cade-by-decade change in each location of the world,” said Alex Ruane, co-director of the GISS Climate Impacts Group and a co-author of the study. The team looked at changes to long-term average crop yields and introduced a new estimate for when climate change im- pacts “emerge” as a discernable signal from the usual, historical- ly known variability in crop yields. Soybean and rice projections showed a decline in some regions but at the global scale the dif- ferent models still disagree on the overall impacts from climate change. For corn and wheat, the climate effect was much clear- er, with most of the model results pointing in the same direction. Corn is grown all over the world, and large quantities are produced in countries nearer the equator. North and Cen- tral America, West Africa, Central Asia, Brazil, and China will potentially see their corn yields decline in the coming years and beyond as average temperatures rise across these breadbasket regions, putting more stress on the plants. Wheat, which grows best in temperate climates, may see a broader area where it can be grown as temperatures rise, including the Northern United States and Canada, North China Plains, Central Asia, Southern Australia, and East Afri- ca, but these gains may level off mid-century. Temperature is not the only factor the models consider when simulating future crop yields. Higher levels of car- bon dioxide in the atmosphere have a positive effect on photosynthesis and water retention, increasing crop yields, though often at a cost to nutrition. This effect happens more so for wheat than corn, which is more accurately captured in the current generation of models. Rising global tempera- tures also are linked with changes in rainfall patterns, and the frequency and duration of heat waves and droughts, which can affect crop health and productivity. Higher tem- peratures also affect the length of growing seasons and ac- celerate crop maturity. “You can think of plants as collecting sunlight over the course of the growing season,” said Ruane. “They're col-