​Terrestrial ecosystems are the main cause of interannual variations in the carbon cycle. Why, then, do they seem to be driven by the tropical temperature when looking at the global scale and by water resources when looking at the local scale?

In a systematic modelling approach, climate scientists have analyzed the effects of temperature and precipitation on carbon exchange between the atmosphere and the terrestrial biosphere, from small areas up to the global surface of the Earth.

Photosynthesis and the respiration of plants and microorganisms are driven by water availability and these effects partially compensate each other. Yet, on a larger scale, the influence of water decreases, since exceptional drought in one part of the world is often compensated by exceptional precipitation in another.

This study points to the need for a better understanding of how climate variables change across different space scales. The simple relationship observed today between temperature and the global land carbon sink should be treated with caution, and should not be used to make long-term predictions. According to the scientists, the water cycle could become a critical factor for the terrestrial carbon sink on a global scale.