When scientists looked closely at larch forests in northern China and ecosystems across the globe, they found something that rewrites what we thought we knew about how nature responds to a warming world. An international team led by Prof. José M. Grünzweig of the Hebrew University of Jerusalem has discovered that plants are not adapting to climate change the way researchers expected—and that shift changes everything about how we predict whether Earth's natural carbon sinks can keep pace with warming.
For decades, climate scientists assumed that as the planet warmed, plants would evolve to photosynthesize best at higher temperatures, a kind of biological tune-up to match the new conditions. If plants succeeded in raising their temperature sweet spot, the logic went, ecosystems would continue absorbing carbon dioxide at rates that could help slow climate change. Land ecosystems are crucial to this equation: they already absorb roughly a quarter of all carbon dioxide released by human activities each year, making them one of Earth's most important natural defenses against warming.
The research, published in One Earth and conducted with collaborators from Peking University and the Weizmann Institute of Science, examined two decades of global data—both ground-based carbon measurements and satellite observations from 2000 to 2019. What the team found was a striking mismatch between what the models predicted and what actually happened. While ecosystems worldwide increased their maximum rates of carbon uptake over the past two decades, the optimal temperature for photosynthesis barely changed, especially in arid and cold regions. Temperature adaptation accounted for less than 20 percent of the global increase in carbon uptake. Something else was driving the change.
That something else turned out to be water and leaves. Plants grew larger canopies and used water far more efficiently, absorbing more carbon dioxide for every drop of water they consumed. This water-use efficiency was the dominant factor everywhere—not just in dry regions but in humid tropical, temperate, and cold environments too. In drier areas, canopy growth emerged as the critical lever shaping how ecosystems respond to warming. Dr. Chongyang Xu noted that the findings were surprising precisely because arid regions showed little evidence of adapting to rising temperatures, yet their carbon uptake continued increasing, driven largely by canopy expansion and ecological restoration programs in some areas.
The implications are profound. Current climate models focus heavily on temperature as the primary driver of ecosystem response. But this research reveals that water management and structural growth—how plants build their canopies—matter far more than scientists recognized. As Prof. Grünzweig explained, "Our study shows that water plays a much bigger role than previously recognized. Understanding how plants use water and build their canopy will be critical for predicting the future of Earth's natural carbon dioxide absorption."
This reorientation matters urgently. As temperatures rise and droughts become more frequent, predicting whether ecosystems will continue absorbing carbon depends less on assuming plants will simply adapt to heat and much more on understanding water availability and growth dynamics. The findings suggest that future climate models must look beyond temperature alone—a fundamental recalibration that could reshape how scientists forecast whether natural carbon sinks will remain strong enough to help stabilize the climate in the decades ahead.