Hotter tropical droughts and potential transition of tropical forests to long-term carbon sources

Determine whether a new regime of hotter droughts in tropical regions will induce a sustained shift in tree mortality that converts tropical forest ecosystems from net carbon sinks into long-term net sources of atmospheric CO2, thereby undermining their climate mitigation role.

Background

The paper reports an exceptional weakening of the global land carbon sink in 2023, driven by extreme heat, widespread drought, severe fires in boreal forests, and a late-year tropical source associated with a developing El Niño. In the tropics, the Amazon experienced an extreme drought in mid-to-late 2023, contributing substantially to the global land sink decline.

While past extreme droughts (e.g., 2015–2016 El Niño) often showed relatively rapid recovery of tropical forest biomass, the paper notes decreasing resilience in the Amazon. Against the backdrop of record warmth and indications of rising drought intensity, the authors explicitly raise the unresolved question of whether a new, hotter drought regime could shift tree mortality dynamics enough to convert tropical forests from net carbon sinks into long-term carbon sources.