Yet the paper shows that the consequences of that methane molecule will last for more than a millennium, causing the the seas to rise higher and higher all the time. That’s because sea-level rise is not only caused by extra water, but by hotter water. As the oceans absorb heat, they expand—and it takes a very long time for this heat to leave.

“The ocean remembers, and that’s really the key message,” says Susan Solomon, an author of the paper and a professor of atmospheric science at the Massachusetts Institute of Technology. “The sea takes a very, very long time to cool down once you’ve heated it up.”

Solomon is a luminary in the field of atmospheric sciences: She led the first Antarctic expedition to study the hole in the ozone layer, and she was among the first to identify how that hole actually formed.

Her and her colleagues’ current finding comes at an unfortunate time: Evidence increasingly suggests that the planet’s methane problem is only getting worse. Last month, an international group of researchers presented a new analysis showing that methane emissions increased after 2007 and began surging in 2014 and 2015. Scientists aren’t yet sure whether melting permafrost, the worldwide growth in natural-gas fracking, or some other source are responsible for the sudden upswing.

The study informs an ongoing discussion among people who care about global warming. Some people advocate for reducing emissions of CO₂, the most abundant greenhouse gas. Carbon dioxide lasts for centuries in the atmosphere, and will be responsible for most of climate change’s ill effects.

But in the short term, carbon dioxide will be aided by “short-lived greenhouse gases,” like methane, nitrous oxide, and the synthetic chemicals called halocarbons. These don’t last longer than a century in the atmosphere, but they can trap much more heat than CO₂. Some think we should tackle them first.

“Our study shows we need to mitigate both as soon as possible. There are no trade-offs,” says Kirsten Zickfeld, an author of the new paper and a professor at Simon Fraser University.

She cited recent research that showed that the heat trapped by gases like methane lasted far longer than 10 years. “There’s this misconception that as we stop emitting these gases, the climate effects will actually go away,” she told me. But that’s not true. Short-lived greenhouse gases, she says, “must be mitigated as soon as possible if future warming and sea-level rise are to be mitigated.”

In their study, Solomon, Zickfeld, and their co-author Dan Gilford projected what would happen if methane emissions accelerated to 2050, and then dropped off entirely. They found that though much of the methane had left the atmosphere relatively quickly, its trapped heat was still causing inches of sea-level rise in 2900.

If emissions of carbon dioxide, nitrous oxide, and methane are all allowed to accelerate to 2050, they could cause three feet of sea-level rise by 2900 through thermal expansion alone. Though they ended their model that year, it showed that the seas would still be rising.