Increased maximum carbon release offsets half of the growth trend in annual land carbon sink.

The terrestrial carbon sink has strengthened in recent decades through enhanced maximum CO2 uptake (MCU) and a longer carbon uptake period (CUP), whereas maximum CO2 release (MCR) remains less quantified. Using atmospheric inversion estimates and 16 terrestrial biosphere models, we show that MCU and MCR both increased significantly from 1993 to 2022, with MCU rising faster globally (0.18 ± 0.04 versus 0.07 ± 0.01 g C m-2 yr-1). MCU increases were widespread, whereas MCR increases were strongest at mid- to high latitudes. Enhanced MCU and CUP increased annual net ecosystem productivity by 0.31 ± 0.09 g C m-2 yr-1, but rising MCR offset 44 ± 20% of this gain, leaving a net increase of 0.18 ± 0.06 g C m-2 yr-1. Elevated CO2 dominates long-term increases, while climate variability contributes to spatial heterogeneity. These findings highlight the importance of accounting for carbon release in projections of future terrestrial sink strength.