Air trapped in ancient Greenland ice has yielded some good, but not great, news about the future on a warming planet, according to a new study.

Wetlands were responsible for a substantial increase in the potent greenhouse gas methane in the atmosphere at the end of the last ice age about 11,600 years ago, the study shows.

The finding is cast as “good news” for the planet because it indicates methane clathrates, an even greater source of methane, remained stable in ocean sediments and permafrost.

“The amount of carbon locked up in methane clathrates is about equal to all the fossil fuels combined, so all of oil, gas, and coal,” study lead author Vasilii Petrenko of the University of Colorado at Boulder told me.

The release of even a small fraction of that methane could supercharge greenhouse warming, he added, which has been a source of worry for the scientific community.

“Our study doesn’t seem to support that. The evidence is suggesting that when the Earth warms, clathrates do not release a lot of methane to the atmosphere and that is really good news,” he said.

In the study, Petrekno and colleagues examined the levels of carbon 14 in methane trapped in an ancient ice sheet in Greenland. The levels were consistent with methane from wetlands, not seafloor deposits.

The results are published this week in the journal Science.

The study suggests that wetlands will release more methane as the planet warms, however, which is of particular concern in the rapidly warming Arctic and subarctic regions.

“There is some evidence in recent methane concentration data that this is already happening as a matter of fact,” Petrenko said.

The amount of methane that can be released from wetlands just isn’t nearly as much as from clathrates locked up in the seafloor and permafrost, he noted.

“We are looking at a lesser of two evils.”