A 300-year record of environmental perchlorate, reconstructed from high- resolution analysis of a central Greenland ice core, shows that perchlorate levels in the post-1980 atmosphere were two-to-three times those of the pre-1980 environment. The record demonstrates that the Industrial Revolution and other human activities, which emitted large quantities of pollutants and contaminants, did not significantly impact environmental perchlorate, as perchlorate levels remained stable throughout the eighteenth, nineteenth, and much of the twentieth centuries. The increased levels since 1980 likely result from enhanced atmospheric perchlorate production.  The enhancement is probably influenced by the emission of organic chlorine compounds in the last several decades.  Brief (a few years) high concentration episodes appear frequently over an apparently stable and low background (~1 ng kg‒1).  Several such episodes coincide in time with large explosive volcanic eruptions including the 1912 Novarupta/Katmai eruption in Alaska. It appears that atmospheric perchlorate production is impacted by large eruptions in both high and low latitudes.