To estimate the magnitude of climate change anticipated for Canada's 38 National Parks (NPs) and Park Reserves, seasonal temperature and precipitation scenarios were constructed for 2050 and 2090 using the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled model (CGCM1). For each park, we assessed impacts on physical systems, species, ecosystems and people. Important, widespread changes relate to marine and freshwater hydrology, glacial balance, waning permafrost, increased natural disturbance, shorter ice season, northern and upward altitudinal species and biome shifts, and changed visitation patterns. Other changes are regional (e.g., combined East coast subsidence and sea level rise increase coastal erosion and deposition, whereas, on the Pacific coast, tectonic uplift negates sea level rise). Further predictions concern individual parks (e.g., Unique fens of Bruce Peninsular NP will migrate lakewards with lowered water levels, but structural regulation of Lake Huron for navigation and power generation would destroy the fens). Knowledge gaps are the most important findings. For example: we could not form conclusions about glacial mass balance, or its effects on rivers and fjords. Likewise, for the East Coast Labrador Current we could neither estimate temperature and salinity effects of extra iceberg formation, nor the further effects on marine food chains, and breeding park seabirds. We recommend 1) Research on specific large knowledge gaps; 2) Climate change information exchange with protected area agencies in other northern countries; and 3) incorporating climate uncertainty into park plans and management. We discuss options for a new park management philosophy in the face of massive change and uncertainty.