Climate change models have underestimated the amount of carbon dioxide that will be emitted from thawing permafrost by as much as 14 percent, according to a new study published in the journal Geophysical Research Letters.
The research incorporates a key pathway for CO2 to enter the atmosphere that is missing from other models: when carbon from thawing permafrost is flushed into waterways and converted to CO2 by sunlight.
Scientists estimate there are about 1,500 billion metric tons of carbon locked away in Arctic permafrost, and that 5 to 15 percent of this carbon could be emitted as carbon dioxide by 2100 — enough to increase global temperatures 0.3 to 0.4 degrees Celsius. But these estimates do not include the CO2 that forms when permafrost carbon escapes into Arctic lakes and rivers and is oxidized by ultraviolet and visible light, a process known as photomineralization.
Researchers at the University of Michigan studied organic carbon from six different Arctic locations and found that substantial carbon dioxide emissions could be released through photomineralization — enough to raise permafrost-related CO2 emissions by 14 percent.
“Only recently have global climate models included greenhouse gases from thawing permafrost soils. But none of them contain this feedback pathway,” Rose Cory, an environmental scientist at the University of Michigan who helped to lead the research, said in a statement.
Scientists have previously been cautious about including photomineralization in their models because it can be difficult to measure exactly how sunlight interacts with soil carbon. But Cory and her colleagues developed a new tool that uses LED lights to measure the impacts of different wavelengths of light on organic carbon. They were then able to determine how light exposure affects the amount of soil carbon converted to CO2 emissions, as well as other factors that might accelerate the reaction. For example, the research team also found that the amount of iron in the soil plays an important role in the photomineralization process.
“What we have long suspected is that iron catalyzes this sunlight-driven process, and that’s exactly what our results show,” Cory said in a statement. “As the total amount of iron increases, the amount of carbon dioxide increases.”