Many national parks in the west areas of America are among the United States, most treasured natural spaces．From Yellowstone to Yosemite, US national parks stand as monuments to Americans, love of nature and our spiritual connection to the land．They are unparalleled sources of beauty and recreation—but for how much longer Twelve US national parks are at serious risk from the increasing effects of global war ruing and the greenhouse effect, according to a report from the National Resources Defense Council (NRDC) and The Rocky Mountain Climate Organization titled, Losing Ground: Western National Park Enered by Climate Disruption.
The report shows how global warming in the dry American West, where temperatures have risen twice as fast as in the eastern United States over the past 50 years, is destroying wildlife habitat, putting specie at risk of extinction, and transforming the landscapes and scenic beauty Americans love．If current trend continue, the report says the glaciers (冰川) in Glacier National Park could all be melted by 2030, along with many of the glaciers and ice caves in the North Cascades National Park, which includes 60 percent o all glacier-covered land in the United States outside Alaska．Within a few years, snow-covered peaks in many parks could be bare of snow throughout the summer, forests, mountain meadows and wildflowers will be sharply reduced; while droughts, wildfires, erosion and floods will increase.
The reports shows the fragile and complex connections that make up natural ecosystems, and how a serious environmental impact from global warming in one area of a national park can begin a chain reaction with devastating effects．For example, as global warming lessens the extreme cold that normally keep mountain bark beetles in check, they are multiplying and infesting whitebark pines (白皮松)—a high altitude species that was previously outside their range—and threatening the trees with extinction．Whitebark pines are an important source of food for gray bears, and their loss would drive the bears into more populated areas in search of food, creating another serious risk to their long term survival.
The building of the national parks in the United States indicates that ______ .