Ancient permafrost submerged in the Arctic Ocean is releasing methane gas into the atmosphere at rates comparable to previous estimates for all the world’s oceans combined, researchers say. This underwater permafrost represents a large but previously overlooked source of methane, and experts say that similar but more widespread emissions of the gas could have dramatic effects on global warming in the future.

The discovery creates “an urgent need” for further research to understand the methane release and its possible impact, researchers say in the new issue of Science.