Dramatic increase in ecosystem respiration causes record-breaking atmospheric CO2 growth rate in 2024

2024 is the hottest year on record, accompanied by extreme precipitation, droughts and fires. The global atmospheric CO2 growth rate (CGR) in 2024 reached a historic high of 3.73 ppm yr-1, significantly surpassing the previous record set during the 2015/16 El Niño event. Here, we investigate the causes and underlying mechanisms of the 2024 record-high CGR by combining satellite-based atmospheric inversions and estimates of gross primary production (GPP) and fire emissions. We find that the record-high CGR was due to large reductions in the land CO2 sink. This was dominated by a dramatic increase in total ecosystem respiration (TER), which occurred primarily in grass and shrub lands, owing to hot-wet conditions and increased autotrophic respiration associated with increased GPP. Given the projected increase in the frequency and intensity of compound pluvial-hot extremes under warming, changes in TER will become more drastic and cause positive feedback to climate warming. This study underscores that ecosystem respiration will increasingly govern the interannual variability of the land sink and atmospheric CGR in the future.