Billions of tons of CO2 could be released from tropical soils

Tropical forest soils are more sensitive to climate change than previously realized. As a result, billions of tons of CO2 could be released into the atmosphere, according to a study from the University of Edinburgh. 

Tropical forests store one-third of the world’s carbon, and the researchers said that CO2 emissions from soils in these forests could increase dramatically if temperatures continue to rise in line with current predictions.

A field experiment conducted in Panama indicates that soil carbon  emissions will increase by 55 percent if average global temperatures rise by four degrees Celsius.

“The results demonstrate the high sensitivity of these ecosystems to warming,” said study lead author Dr. Andrew Nottingham. “It should be a wake-up call for us to take action to mitigate climate change and preserve tropical forests, which are one of the most important components in Earth’s carbon cycle.”

Carbon is released from soils during microbial activity and decomposition. The amount of CO2 that could be emitted from tropical soils is potentially so large that it would trigger additional global warming in a reinforcing feedback loop.

Previous studies have shown that rising temperatures threaten to release carbon locked away in frozen soils, such as Arctic permafrost. Prior to this study, however, tropical soils were thought to be more resilient to climate change.

The research team conducted a large-scale experiment in a tropical forest on Barro Colorado Island in the Panama Canal. 

The experts built heating devices and buried them one meter into the soil. The system was fitted with heating cables and a thermostat. For two years, the equipment kept the experimental areas four degrees warmer than the surrounding soil.

The findings show that, from every single hectare of tropical forest, up to eight extra tons of soil carbon will be released in the form of CO2 each year as temperatures rise.

While the researchers expect that the rate of emissions will eventually decline in the experimentally warmed soils, they do not yet know how long this will take. The long-term impact of soil warming on climate change is also unclear.

The team will continue the experiment – the Soil Warming Experiment in Lowland Tropical Rainforest (SWELTR) – to better understand how tropical forests are responding to global warming.

Study co-author Professor Patrick Meir concluded that the carbon emissions from warming tropical forest soils are much higher than expected, which shows that there is a need to re-examine current predictions.

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer