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

Authors: YU, ZHONGJIE - UNIVERSITY OF MINNESOTA; GRIFFIS, TIMOTHY - UNIVERSITY OF MINNESOTA; BAKER, JOHN

Submitted to: Communications Earth & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 3/5/2021
Citation: Yu, Z., Griffis, T.J., Baker, J.M. 2021. Warming temperatures lead to reduced summer carbon sequestration in the U.S. Corn Belt. Communications Earth & Environment. 2. Article 53. https://doi.org/10.1038/s43247-021-00123-9.
DOI: https://doi.org/10.1038/s43247-021-00123-9

Interpretive Summary: Changes in the annual seasonal cycle of atmospheric CO2 concentration can provide important information about the way in which the earth is responding to changes in climate. It is generally known that the amplitude of this signal has increased in recent years, and the summer drawdown in the northern hemisphere is also well-documented, suggesting that there has been a positive response of CO2 uptake to warming. However, there is still considerable uncertainty about this response and particularly whether it will continue. We have analyzed a decade-long data set of precision measurements of CO2 concentration made from a tall radio tower in southern Minnesota. By combining these data with measurements made at towers in the neighboring states of Wisconsin and Iowa and applying atmospheric inversion modeling we show that crop production in the U.S. Corn Belt has had a strong and coherent effect on the regional CO2 cycle. Significantly, warming has had a strong positive impact on CO2 uptake early in the growing season, but has reduced uptake in both cropped regions and natural ecosystems during the peak portion of the growing season. This negative impact appears to be amplified by a limitation of water availability, suggesting that these ecosystems are operating at their optimal temperatures, and that further warming may decrease productivity by 2050, reducing the amplitude of the peak by 10% and reducing net CO2 uptake by 11%. These data should be valuable in predicting further impacts of projected changes in climate.

Technical Abstract: The seasonal cycle of atmospheric CO2 provides an integrative measure to probe the terrestrial carbon cycle dynamics and its interactions with climate. The annual amplitude and growing season drawdown of atmospheric CO2 in the northern hemisphere have increased significantly since the 1960s, indicating a warming-driven intensification of net CO2 uptake in northern terrestrial ecosystems. However, gaps remain in our understanding on how CO2 exchange of croplands and natural terrestrial ecosystems at northern temperate latitudes are responding to ongoing and future climate change. Here we present a decadal time series (2007 to 2019) of hourly CO2 concentration measured at a very tall tower within a heterogeneous agricultural landscape in the United States Corn Belt. Combining this decadal record with other long-term CO2 time series and atmospheric inversion products within the region, we show that crop production had a large and spatially coherent imprint on the regional CO2 seasonal cycle. Warming had a positive impact on net CO2 uptake during the early crop growth stage but reduced net CO2 uptake in both croplands and natural ecosystems during the peak growing season. The negative temperature impact was further amplified by limitation on water availability, indicating that these ecosystems are currently operating at their thermal optima of ecosystem productivity. Warming by 2050 tends to attenuate the CO2 seasonal amplitude by 10% and net CO2 uptake by 11% in the Corn Belt. Collectively, these findings suggest that both magnitude and timing of future warming are important in determining net CO2 sequestration in northern mid-latitude ecosystems.