The study was published on Monday in the Proceedings of the National Academy of Sciences.
The aircraft measurements, which include more of Alaska and were taken from 2012 to 2014, suggest that the boreal forest covering much of the southern half of the state remains a net storehouse of carbon dioxide. But the amounts stored are more than offset by the increasing tundra emissions, the researchers conclude.
Steven C. Wofsy, a Harvard professor and an author of the paper, said the findings suggested that the state was becoming a source of carbon dioxide. “But it doesn’t prove that yet,” he said.
Warmer temperatures can lead to more plant growth, which would increase the takeup of carbon dioxide from the atmosphere through photosynthesis. Scientists have reported that this “greening” of the Arctic is occurring as temperatures increase.
But as this study shows, by delaying freeze-up, warming may also allow processes that release carbon dioxide to continue longer.
Arctic and near-Arctic soils contain as much or more carbon, in the form of dead vegetation that has accumulated for centuries, than is currently in the atmosphere. By adding some of that carbon back into the atmosphere, a shift from sink to source could intensify warming, potentially leading to even more emissions.