n Alaska’s Brooks Range, rivers once clear enough to drink from now run orange and hazy with toxic metals. As warming thaws formerly frozen ground, it sets off a chemical chain reaction that is poisoning fish and wreaking havoc on ecosystems.

As the planet warms, a layer of permafrost — permanently frozen Arctic soil that locked away minerals for millennia — is beginning to thaw. Water and oxygen creep into the newly exposed soil, triggering the breakdown of sulfide-rich rocks, and creating sulfuric acid that leaches naturally occurring metals like iron, cadmium, and aluminum from rocks into the river.

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