This talk examines the history of environmental data systems in the context of the current US administration’s assault on environmental science. Tracking and understanding environmental change requires scientific memory, aka “long data”: consistent, reliable sampling over long periods. Weather observations can become climate data, for example — but only if carefully curated and adjusted to account for changes in instrumentation and data analysis methods. Environmental knowledge institutions therefore depend on an ongoing truce among scientific and political actors. For at least 25 years, climate denialism and deregulatory movements have sought to destabilize this truce, which nevertheless has held until recently. Since 2017, however, climate change deniers and non-scientist ideologues have been appointed to lead key American knowledge institutions. These leaders, and the White House itself, view certain environmental data systems as targets, which they may yet succeed in crippling or completely dismantling. These developments threaten the continuity of the “long data” vital to tracking climate change and other environmental disruptions, with significant consequences for both domestic and international security.