Revision with unchanged content. Tourism is one of the largest industries in the world, and since it is directly affected by weather, it is dependent upon weather and climate, particularly the length and quality of the outdoor recreation season for nature-based tourism. Indirectly, the natural biophysical resources that outdoor tourism is based upon can also be altered by climate. Thus, climate change has the potential to affect nature-based tourism that takes place in national parks and other protected areas. This study applies a single variable regression analysis technique to empirically evaluate the affects of climate change on the quantity and seasonal patterns of visitation to United States national parks under a range of climate change scenarios for the 2020s, 2050s, and 2080s. Changes in visitation patterns could lead to the need for substantial management changes in certain United States national parks as revenue collected from user fees and operational costs are altered. The results of the study will be particularly useful to the United States National Park Service and other regional and park managers to plan for visitation changes that might occur as climate change continues over the 21st century.