Warming increases ecosystem carbon emissions – but only with sufficient rain

The emissions of carbon dioxide from ecosystems are known to be higher in warmer climates. Therefore, global warming can speed up emissions, causing a stronger greenhouse effect that worsens climatic changes. But only in sufficiently moist environments where plants and soil organisms are not limited by water availability, as shown in a Nature Ecology & Evolution article with four co-authors from Stockholm University. 

“All organisms need water to live and both plants and soil microorganisms lower their metabolism in dry conditions. As a result, ecosystems release less carbon dioxide when soils are dry”, said co-author Stefano Manzoni, associate professor at the Department of Physical Geography, Stockholm University. 
 
So far, most research focused on temperature — and for good reasons, as warmer conditions increase metabolic rates and thus emissions. The new study in Nature Ecology & Evolution highlights the critical role of water in this feedback loop. It demonstrates for the first time the existence of precipitation thresholds for keeping the soil sufficiently moist to sustain the positive feedback from enhanced ecosystem metabolism. Below the thresholds, metabolic rates will not anymore speed up by further warming and worsen climate change. These threshold values vary across the world’s climate zones, since more precipitation is needed in warm regions to keep the ecosystem moist. This is why the water cycle is central to determine how much carbon dioxide is emitted.
 
This finding has major implications since precipitation may fall short of the threshold in considerable world regions, which then might be less sensitive to warming because water becomes the most limiting factor. 
 
“To refine our understanding of where and when water becomes limiting, as well as the net impact on carbon dioxide emissions, we need to focus our research efforts on hydroclimate and future water cycle changes,” concludes co-author Jerker Jarsjö, professor at the Department of Physical Geography, Stockholm University.  
 
The study

The study, “Water limitation regulates positive feedback of increased ecosystem respiration,” published August 7 in Nature Ecology & Evolution, was led by Jin Zhang, a PhD student at Dalian University of Technology who conducted this research while visiting the Department of Physical Geography at Stockholm University. 
DOI: 10.1038/s41559-024-02501-w
 
Contact information

Stefano Manzoni stefano.manzoni@natgeo.su.se +46-8-674 78 02
Gia Destouni georgia.destouni@natgeo.su.se +46-8-16 47 85
Gustaf Hugelius gustaf.hugelius@natgeo.su.se +46-8-674 78 73
Jerker Jarsjö jerker.jarsjo@natgeo.su.se +46-8-16 49 58