Researchers Take Closer Look at Link Between Permafrost Thaw and Greenhouse Gases

In a new study published in the journal Nature Climate Change, researchers explain in greater detail than ever before how the thawing of the world's permafrost may result in a substantial release of carbon dioxide into the atmosphere, and that crucial in predicting the overall effect of the process is the soil's water content.

Knowing this, the researchers argue, may lead to more accurate climate models in the future.

Permafrost, soil or rock that remains frozen all year round, occurs where the warmer summer months fail to penetrate the ground enough to thaw it. And while the depth to which this frozen encasement reaches can vary widely, scientists warn that overall it's thinning at both poles -- and quickly.

Just how much carbon is trapped in the ever-frozen soils of the world isn't entirely clear, though one study published in 2009 estimates it holds roughly 1,700 billion tons, or roughly twice the total amount of carbon currently in the air.

What scientists are sure about, though, is that as the ice thaws, microbial activity picks up, resulting in a large amount of carbon respired into the atmosphere as CO2 and, though to a lesser degree, methane.

As this happens, a positive feedback loop is created as rising greenhouse gases lead to even more thawing of permafrost.

Despite this imposing threat, the rate at which CO2 is released from permafrost has long remained poorly documented, making it one of the most glaring uncertainties in current climate models.

Knowing that current estimates are based on measurements taken over periods of just a few months, a team of Danish researchers decided to study the process over the course of 12 years.

"From a climate change perspective, it makes a huge difference whether it takes 10 or 100 years to release, e.g., half the permafrost carbon pool," study lead Bo Elberling said, explaining that they were able to show that "the supply of oxygen in connection with drainage or drying is essential for a rapid release of carbon dioxide into the atmosphere."

Also important is the future water content in the soil if climate models are to accurately predict the effect of permafrost thawing, Elberling points out. If the permafrost remains water-saturated after thawing, carbon decomposition rate will be very low, and the release of carbon dioxide will be staggered over a period of several hundred years along with methane, which is produced in waterlogged conditions.

"It is thought-provoking that microorganisms are behind the entire problem -- microorganisms which break down the carbon pool and which are apparently already present in the permafrost," Elberling said. "One of the critical decisive factors -- the water content -- is in the same way linked to the original high content of ice in most permafrost samples."

Based on this and their observations, Elberlin concludes that "Yes, the temperature is increasing, and the permafrost is thawing, but it is, still, the characteristics of the permafrost which determine the long-term release of carbon dioxide."