Trapped in all that permafrost is an estimated 30 billion tons of carbon. It’s an unfathomable amount, Kirkwood says. With global warming, the permafrost is thawing, threatening to release a “carbon bomb” of heat-trapping methane gas into the atmosphere. But there’s something else lurking in the permafrost that has the potential to be more immediately dangerous to the people and wildlife living in the area: mercury.