The study this story is based on is available online: http://bit.ly/iEvLhh

A new study concludes that models may be predicting releases of atmospheric carbon dioxide that are either too high or too low, depending on the region, because they don’t adequately reflect variable temperatures that can affect the amount of carbon released from soil.

The study points out that many global models make estimates of greenhouse gas emissions from soils based on “average” projected temperatures. But temperatures vary widely from those averages. That variability, along with complex biological processes, makes the issue far more complicated.

Researchers said that climate projections, in general, don’t effectively incorporate into their calculations a major component of global warming – the enormous amounts of carbon found in dead, decaying organic matter, which represent up to three times the amount of carbon in the Earth’s live vegetation.

The study was just published in the journal Biogeosciences by scientists from the College of Forestry at Oregon State University and other institutions.

“We’ve done a pretty good job of determining how much carbon is getting absorbed by growing trees and  vegetation, how much is coming in,” said Mark Harmon, professor and holder of the Richardson Chair in Forest Science at OSU, and one of the world’s leading experts on the effect of decomposition on the Earth’s carbon cycle.

“However, we know much less about how carbon is released to the atmosphere through the process of decomposition, how much is going out,” he said. “This is half of the equation, and there’s just a huge amount we don’t know about it.”

These findings don’t change the fact that atmospheric carbon dioxide and other greenhouse gas levels are increasing and global warming is a reality, Harmon said. But they do suggest that some of the projections, particularly those made by older models that incorporate even less variability into their analysis, may be flawed.

“This work is important because it brings attention to a component of climate change that was often ignored in the past,” said Carlos Sierra, previously an OSU doctoral student, lead author on the study and now a researcher with the Max-Planck-Institute for Biogeochemistry in Germany. “We can make better projections if we add changes in temperature variability to the equation.”

Researchers have understood, and have been concerned for some time, that warmer temperatures will speed up the rate of decomposition of stored organic matter in soils, a process that ordinarily is slow. This faster rate of decomposition, in turn, could further increase carbon released to the atmosphere and cause even greater global warming.

“This feedback loop is one of our biggest worries with global warming, simply because the amount of carbon stored in soil is so huge,” Harmon said. “Increased release of that soil carbon could offset much of what we’re trying to accomplish with increased growth of live vegetation in forests. And this is a special concern in northern latitudes.”