How close are we to the temperature tipping point of the terrestrial biosphere?

The temperature dependence of global photosynthesis and respiration determine land carbon sink strength. While the land sink currently mitigates similar to 30% of anthropogenic carbon emissions, it is unclear whether this ecosystem service will persist and, more specifically, what hard temperature limits, if any, regulate carbon uptake. Here, we use the largest continuous carbon flux monitoring network to construct the first observationally derived temperature response curves for global land carbon uptake. We show that the mean temperature of the warmest quarter (3-month period) passed the thermal maximum for photosynthesis during the past decade. At higher temperatures, respiration rates continue to rise in contrast to sharply declining rates of photosynthesis. Under business-as-usual emissions, this divergence elicits a near halving of the land sink strength by as early as 2040.

Automated summary

The temperature dependence of global photosynthesis and respiration influences the strength of land carbon sink, with the average temperature of the warmest quarter exceeding the thermal maximum for photosynthesis over the past decade, leading to a potential halving of land sink strength in the future.