As climate change continues to warm the world’s polar regions, the gas trapped below the surface of the ice and permafrost is released at an increasing rate. According to a report from the Washington Post, a recent study from researchers at San Diego State University have reached a startling realization; the rate at which this gas has been released in recent years has been grossly underestimated by climate researchers.

Permafrost in the Arctic is soil that has never been in a state other than frozen solid; it contains large quantities of organic material that have more or less been preserved since the soil first formed thousands of years ago. As permafrost thaws, so does this ancient organic material. As it decomposes, it emits unfathomable quantities of methane.

Scientists are just starting to wrap their heads around how much methane is actually being released as the Arctic permafrost thaws. The majority of recent permafrost research has focused on how it behaves during the warmer summer months in the Arctic, but the recent paper published in the Proceedings of the National Academy of Science examined how much methane is being released into the atmosphere during the cold season. Spoiler alert: it’s more than anyone previously suspected.

According to lead author Donatella Zona, assistant professor from San Diego State University, “The cold period in general is the time of the year that is warming the fastest in these arctic ecosystems. Really, if we’re thinking about the future of climate change, we need to understand if this time of the year is important.”

Along with a group of almost 20 other scientists, Zona collected data from five different monitoring sites in Alaska between June 2013 and January 2015. They also examined data collected by aircraft over the same time period. The study found that during the cold season, methane emissions were shockingly significant. Emissions from September to May made up almost half of the methane emissions from the monitoring sites over the entire year.

Methane emissions from permafrost are an example of a positive feedback loop. As the temperature warms in the Arctic, the ice melts faster and releases more methane. As more methane is released into the atmosphere, more solar radiation is trapped, which leads to further warming. If researchers can’t find a way to slow the warming of Arctic permafrost, the climate consequences may be dire.

A press release from NASA’s Jet Propulsion Laboratory outlining the details of the study can be found here.