Drought affects levels of carbon dioxide in the atmosphere more than was previously thought, because stressed eco-systems absorb less of it, say Swiss, French and British researchers. 

This needs to be taken into account in future climate models, said the federal technology institute ETH ZurichExternal link on Wednesday. 

The researchers from ETH Zurich, the Laboratory of Climate and Environmental Sciences in France and the University of Exeter, UK, publish their findings in the August 30 edition of British science review NatureExternal link.   

Terrestrial ecosystems absorb 30% of human CO2 emissions on average, but during dry spells plants reduce their photosynthesis and thus their absorption of CO2 from the surrounding air, they say. 

For example, in 2015, which was particularly dry, ecosystems absorbed 30% less CO2 from the atmosphere than in a normal year. In 2011, which was wet, the opposite happened, with a slowdown in rising concentrations of CO2. 

The scientists were able to use new satellite observations of water to measure the overall impact of droughts on photosynthesis and ecosystem respiration. 

When there is a major drought in a given region, there is less water mass, and gravity is consequently slightly weaker over that region. Such variations are so small that they are imperceptible to humans. But by measuring them with satellites, scientists are able to estimate large-scale changes in water storage to an accuracy of about four centimetres everywhere on the planet. 

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