A multinational research group led by atmospheric scientists at Colorado State University has uncovered new information regarding the Earth’s carbon dioxide sources and sinks, according to a report in today’s Nature journal. Among other results, the researchers conclude that North America may not be absorbing as much carbon dioxide as previously reported.
Sixteen leading research teams in carbon transport modeling from the United States, Germany, France, United Kingdom, Japan and Australia are participating in the TransCom 3 project. The group is completing a three-year study aimed at helping to resolve a controversy concerning the mysterious removal of a large amount of carbon dioxide from the Earth’s atmosphere known as the missing sink.
In recent years, the missing sink has partially offset the large amount of carbon dioxide – the dominant contributor to global warming – emitted into the Earth’s atmosphere.
"Something on land in the Northern Hemisphere is sucking up carbon," said Kevin Gurney, lead author of the paper and a research associate at Colorado State. "This missing sink is not a new phenomenon, but where it is and how it works has long remained a mystery. Unraveling this mystery is essential if we are to reliably predict future levels of carbon dioxide build-up and the resultant global warming."
The TransCom 3 research team agrees with previous reports that there is a large carbon dioxide sink on land in the Northern Hemisphere. However, contrary to a recent, widely cited study, the group does not believe the sink is entirely in North America.
"Our research found carbon uptake over the Northern Hemisphere continents distributed relatively evenly across North America, Europe and temperate Asia," said A. Scott Denning, assistant professor of atmospheric science at Colorado State and coordinator of the TransCom 3 project. "We found the North American sink approximately 60 percent of the size suggested in the earlier study, as well as other large carbon sinks in Europe and Asia."
TransCom 3 also concluded that the southern ocean, long considered by oceanographers to be a massive carbon sink, is not as large as what has been suggested. According to the study, the ocean is taking up less carbon dioxide, and landmass, specifically in the Northern Hemisphere, is absorbing more than previously thought.
The research team additionally forwarded two conclusions that could improve future research into carbon dioxide sources and absorption. First, prioritizing where and how to make more measurements needs to be a priority when studying the tropics due to a lack of data in those areas. Second, for more accurately studying the Northern Hemisphere, efforts need to be focused on improving scientific air-flow transport models.
"If, for example, the goal is to improve the understanding of sinks in the northern continents, where the majority of us live, then the most important thing to do is to put resources toward improving air-flow models," said Denning. "However, even if you had really good models in the tropics, you would still be out of luck because of the lack of data."
TransCom 3 combined a database of CO2 measurements at 76 sites throughout the world with global wind information to determine where carbon dioxide comes from and where it is absorbed. Through inverse modeling and a unique, unified scientific approach, the group was able to map the sources and sinks of carbon dioxide in 22 regions: 11 on land and 11 at sea.
"What is so encouraging about these results is how robust they are to many of the assumptions used," said Gurney. "By enlisting the cooperation of the worldwide carbon-modeling community, the project was less sensitive to details that plague other studies."