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Accurately predicting the responses of gross primary productivity (GPP) to warming is essential for constraining the global carbon cycle and its feedback to climate change. GPP increases with temperature but declines beyond a threshold, known as the ecosystem optimum temperature ( T o p t e c o ). A realistic representation of T o p t e c o is therefore crucial for reliable projections of GPP and terrestrial carbon uptake. However, whether current Earth system models (ESMs) capture T o p t e c o remains unclear. Here, we evaluated ESMs' representation of T o p t e c o and its temporal trends using ground observations and remote-sensing products from 1982 to 2013. We found that ESMs overestimated or failed to capture T o p t e c o across 60.3% of ecosystems, especially in arid regions, due to misrepresented water limitations and vegetation structure changes under high temperatures. Furthermore, ESMs underestimated the observed temporal increase in T o p t e c o , indicating their limited capacity to replicate ecosystem temperature acclimation. These findings reveal significant uncertainties in GPP projections and offer critical insights to improve carbon-climate feedback predictions.
Wang et al. (Tue,) studied this question.