Climate change — aka, global warming, which virtually every credible scientist has agreed is mankind’s doing — is most often associated with the melting of ice near our planet’s poles. That ice melt has been speeding up in recent decades and shows no sign of slowing. When that ice melts, it causes sea levels to rise and the sea floor to be pushed deeper, both of which are very bad things if we want to keep living where we’re living. Now, a new potential threat from global warming has emerged, and this time it’s truly toxic.

New research into the composition of the frozen ground in the Arctic has revealed the single largest reserve of mercury on the planet. Mercury, a toxic metal that has been regulated the world over due to its ability to poison wildlife as well as humans, is locked in the Arctic permafrost, and has been safely contained there for the entirety of human civilization. As worldwide temperatures rise, that will change, releasing as much as 15 million gallons of mercury.

The study, which was published in Geophysical Research Letters, utilized core samples from the Arctic permafrost to gauge the level of various materials and elements. What the scientists found was a wealth of mercury that has no rival. The amount of mercury locked in the frozen ground of the Arctic dwarfs all the mercury mankind has ever used by a factor of ten, and is roughly double the estimated amount of mercury that is currently present in the rest of the ground, water, and air of the entire planet.

Scientists already know how harmful mercury can be to life. It can cause severe damage to organs including the brain, and because it builds up in the bodies of animals rather than passing through, it is easily carried up the food chain. The mercury content of fish has been a major health concern for humans for decades, and the higher the fish is on the food chain the more likely it is to be carrying a high concentration of mercury.

Needless to say, the release of millions of gallons of mercury into ocean water from melting permafrost could be catastrophic to sea life and everything that relies on it, including the human race. Now more than ever, it seems our survival depends on keeping the planet from getting any hotter.