As carbon dioxide in the atmosphere increases, the soil releases ever more of two other potent greenhouse gases, new research has found.
An international team of researchers carried out a meta-analysis of data covering a variety of different environments - from forests to rice paddies - to examine how an increase in carbon dioxide affects the release of methane and nitrous oxide.
"Until now, there was no consensus on this topic, because results varied from one study to the next," says Professor Craig Osenberg of the University of Florida.
"However, two strong patterns emerged when we analysed all the data: firstly more CO2 boosted soil emissions of nitrous oxide in all the ecosystems, and secondly, in rice paddies and wetlands, extra CO2 caused soils to release more methane."
The increase is caused by specialised microscopic organisms in soil which respire the chemicals nitrate and carbon dioxide. They also produce methane, a greenhouse gas 25 times more powerful than carbon dioxide, and nitrous oxide, 300 times more potent than carbon dioxide.
Increased CO2 in the atmosphere reduces plant water use and makes soils wetter, reducing the availability of oxygen in soil and favoring the microorganisms.
It also makes plants grow faster, and the extra plant growth supplies soil microorganisms with extra energy, pumping up their metabolism. This pheomenon partically counteracts the mechanism whereby increased plant growth mops up more CO2.
"This feedback to our changing atmosphere means that nature is not as efficient in slowing global warming as we previously thought," says Dr Kees Jan van Groenigen of Trinity College Dublin.