Ecosystem CO₂ uptake: Prolonged after-effects of an extremely warm year. Earth's terrestrial ecosystems strongly modulate levels of CO₂ in the atmosphere through seasonal changes in net plant productivity (CO₂ absorbance) and soil microbial respiration (CO₂ release). It has been known for decades that these processes respond to seasonal shifts in climate, especially temperature, resulting in the zig-zag form of the global CO₂ curve, but the data necessary to quantify impacts of a single climate variable at interannual timescales have been lacking. A four-year study using intact tallgrass prairie ecosystems in controlled environment chambers (like the one on the cover, showing plant communities a few weeks after summer mowing) now provides some of the missing data. The results show that one anomalously warm year reduces net ecosystem CO₂ exchange for that year and the year after. Carbon sequestration in ecosystems exposed to high temperatures for a year is a third of that in controls. These findings suggest that more frequent anomalously warm years, a possible consequence of rising anthropogenic CO₂ levels, could lead to a sustained decrease in CO₂ uptake by terrestrial ecosystems. Cover photo: J. Arnone [Letter p. 383; www.nature.com/podcast]