Hebrew University study: plants absorb more CO2 by saving water, not by adapting to heat

An international study led by Prof. José M. Grünzweig of the Hebrew University of Jerusalem has found that the world's vegetation has been absorbing more carbon dioxide mainly because plants are growing more leaves and using water more efficiently, not because they are adapting to higher temperatures. The work, published in the journal One Earth and announced on June 3, 2026, was carried out with Dr. Chongyang Xu of the Hebrew University's Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Prof. Dan Yakir of the Weizmann Institute of Science, Prof. Hongyan Liu of Peking University and colleagues in several other countries.

Plants take up roughly a quarter of the carbon dioxide released by human activity each year, making them one of the planet's most important brakes on global warming. Many climate models assume that ecosystems keep pace with warming by shifting the temperature at which photosynthesis works best. To test this, the team combined ground-based carbon measurements with satellite observations covering 2000 to 2019.

They found that the maximum amount of carbon that land ecosystems can absorb did rise over those two decades, but the optimal temperature for photosynthesis barely moved, especially in dry and cold regions. Changes in that optimal temperature explained less than 20 percent of the global increase. Instead, the main drivers were expanding leaf cover and greater water-use efficiency, meaning plants captured more carbon for each unit of water they lost. This pattern held even in humid tropical and temperate regions. In arid areas, uptake grew largely because canopies expanded, helped in some places by ecological restoration programs.

The authors say climate models that rely mainly on temperature responses may misjudge how much carbon the land will absorb in the future, particularly as droughts become more frequent, and that carbon-offset projects should account more carefully for water availability. Grünzweig stressed that the findings do not reduce the need to cut emissions, but they show that plants have more than one way to keep helping.