Tropical forest soil warmed in experiments to levels consistent with end-of-century temperature projections released 55 percent more CO2 than control plots, exposing a previously underestimated source of greenhouse gas emissions, researchers reported on Wednesday.

Photo taken on August 5, 2018 shows the Rhone Glacier covered with white blankets near the Furka Pass in Switzerland. The Rhone Glacier is protected by special white blankets to prevent it from further melting as a result of global warming. Photo: Xinhua

Before humanity began loading the atmosphere with carbon pollution by burning fossil fuels, the input and outflow of CO2 into soil - one key element in Earth's complex carbon cycle - remained roughly in balance. 

Gases emitted by deadwood and decaying leaves, in other words, were canceled out by microorganisms that feed on such matter. But climate change has begun to upset that balance, according to a new study, published in Nature.

"Carbon held in tropical soils is more sensitive to warming than previously recognized," lead author Andrew Nottingham, a researcher at the University of Edinburgh's School of Geosciences, told AFP.  

"Even a small increase in respiration from tropical forest soils could have a large effect on atmospheric CO2 concentrations, with consequences for global climate."

The quantity of carbon cycling each year through soils worldwide is up to 10 times greater than human-generated greenhouse gas emissions.

Just a one-percent imbalance - with more carbon going out than in - "would equal about 10 percent of global anthropogenic [man-made] carbon emissions," noted Eric Davidson, a researcher at the University of Maryland Center for Environmental Science.

Earth's average surface temperature has risen just over 1 C above preindustrial levels, enough to boost the severity of droughts, heat waves and superstorms made more destructive by rising seas.