Ancient pathogens that have been preserved in northern Russia’s permafrost for millennia could reawaken as global temperatures rise, scientists warn, potentially putting humanity at risk of never-before-seen diseases. Jean-Michel Claverie, a virologist and emeritus professor at the Aix-Marseille University School of Medicine, is one of the few scientists worldwide who has studied “zombie viruses” in the Siberian permafrost. He warned they could be present in Russia’s frozen soil in a “very large number and diversity.”