Human disruption of the climate is the greatest threat ever to our national parks. This report focuses primarily on 25 national parks that we identify as having the greatest vulnerabilities to human-caused climate change. They face 11 different types of risks. A loss of ice and snow is one of the most obvious impacts of a changing climate. Glaciers are melting in our national parks, a handful of which contain the vast majority of the nation’s glaciers. In many national parks, snow-covered mountains contribute to some of the most spectacular scenery in the nation. But higher temperatures, less snowfall, and earlier snowmelt are already leading to declines in mountain snowpack across the West. With less snow, fewer visitors will be able to see snow-capped mountains in parks. Opportunities for cross-country skiing, snowshoeing, and other winter activities in parks also will be reduced. (See pages 7-10.) For a summary of how losses of ice and snow, and other impacts, are already underway in national parks, see the next page. Parks in the West and along the Great Lakes face a loss of water. In the West, a changed climate will reduce water availability, especially in the summer. The Colorado Plateau, home to our largest concentration of national parks, is expected to get particularly hotter and drier. In Zion National Park, reductions in river flows could change how the Virgin River is continuing to shape Zion Canyon. Water levels of the Great Lakes are likely to fall, affecting ecosystems and recreation in Great Lakes parks. (See pages 11-14.) The 74 national parks on our coasts face higher seas and stronger coastal storms. Depending on future emissions of heat-trapping gases, seas are expected to rise from about 2.3 feet to 3 or 4 feet by century’s end. Nearly all of Everglades, Biscayne, and Dry Tortugas national parks and Ellis Island National Monument are less than that above the current sea level. All four parks could be lost to rising seas, representing the first-ever losses