Once champions of global conservation, the United States and Brazil are now leading a troubling global trend of large-scale rollbacks in environmental policy, putting hundreds of protected areas at risk, a new study suggests. According to the report - perhaps the most comprehensive review to date of the extent of the legal processes also known as protected area downgrading, downsizing and degazettement, or PADDD - the regressive changes seek to legally alter or remove protected status and decrease the size of established natural conservation areas. Protected areas (PAs), which cover nearly 15% of the planet's terrestrial surface, were created with the goal of conserving Earth's natural areas and their resident biodiversity. While not all PADDD events are harmful to biodiversity, including those initiated to accommodate indigenous claims, the majority of recent events, often related to permitting industrial-scale resource extraction, have been harmful. Rachel Golden Kroner and colleagues conducted a comprehensive review of more than 140 years of PADDD events worldwide with specific attention on the U.S. and Amazonia. The results show that nearly 2 million square kilometers of global protected area have been "PADDDed" since 1892 - 78% of which has occurred since the year 2000. In the US alone, 90% of proposed PADDD events have been introduced since 2000, 99% of which were for industrial-scale development. These include the Trump administration's proposed reductions to the Bears Ears and Grand Staircase-Escalante National monuments by 85% and 51%, respectively, as well as the U.S. Congress' recent decision to allow oil and gas development in Arctic PAs. Golden Kroner et al. suggest that these decisions from influential governments could embolden other countries to do the same and seriously threaten PAs worldwide. In a related Perspective, Lisa Naughton-Treves and Margaret Buck Holland discuss when downgrades threaten biodiversity, and when they do not, and the importance of recognizing these processes in PA management.