Air bubbles confirm permafrost CO2 release
Permafrost melt Bubbles of air trapped in ice long ago are helping paint a clearer picture of what may happen to atmospheric carbon dioxide levels in the future if climate change melts the northern hemisphere's permafrost, scientists say.
An international team set out to answer a long-standing question about why carbon dioxide levels have changed so much as the Earth has cycled between cooler and warmer intervals in the distant past.
The Earth's climate has moved from these cold and warm phases (known as glacial and interglacial periods) several times, with the last glacial period ending about 15,000 years ago.
"During all the interglacial periods, we've had atmospheric carbon dioxide levels of about 280 parts per million, and during the glacial periods it's been down to about 180 or 160," says Harrison.
"Our real problem has been understanding where the carbon comes from that is released into the atmosphere during that warming process."
To answer this question, the researchers looked at the proportions of different forms of oxygen in bubbles of air trapped in ice during these time periods.
"There are different forms of oxygen, and as that oxygen in the carbon dioxide molecules is being moved around between different sources, you get different proportions of those different forms," Harrison says. "You can use that change to tell you where the carbon dioxide is coming from."
Combining this information with climate models, the researchers concluded that the extra carbon dioxide was being released from vegetation, particularly tundra and cold steppes, which are very rich in carbon.
"These plants were stocking carbon in the soil, and when the climate started warming at the end of the glacial period, that carbon was released into the atmosphere," Harrison says.
Scientists know that there is carbon locked up in permafrost and permafrost soils at high northern latitudes today. They also expect that as the climate warms in the future, that carbon is going to be released and increase the amount of carbon dioxide in the atmosphere.
But without being able to explain exactly the natural carbon dioxide changes in the past, they have been hesitant about projecting exactly what the impact might be. "You do wonder if there are things you don't understand about the system," Harrison says.
"Essentially what this paper is saying is that we now have a much better understanding of what was happening in the past through the use of these modelling tools and these measurements."
The new findings will help scientists develop more accurate models of what will happen to atmospheric carbon levels as the permafrost melts.
"We are really beginning to understand the natural variations in carbon dioxide much better than we did before. In terms of projecting what might happen in the future we now have more confidence in our ability to do that."