Warming temperatures lead to reduced summer carbon sequestration in the U.S. Corn Belt

The response of highly productive croplands at northern mid-latitudes to climate change is a primary source of uncertainty in the global carbon cycle, and a concern for future food production. We present a decadal time series (2007 to 2019) of hourly CO₂ concentration measured at a very tall tower in the United States Corn Belt. Analyses of this record, with other long-term data in the region, reveal that warming has had a positive impact on net CO₂ uptake during the early crop growth stage, but has reduced net CO₂ uptake in both croplands and natural ecosystems during the peak growing season. Future increase in summer temperature is projected to reduce annual CO₂ sequestration in the Corn Belt by 10–20%. These findings highlight the dynamic control of warming on cropland CO₂ exchange and crop yields and challenge the paradigm that warming will continue to favor CO₂ sequestration in northern mid-latitude ecosystems.