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Following a pair of recent studies that exposed man-made and climate-caused deterioration at those two iconic American attractions, environmentalists are raising new concerns about the future health of all 58 U.S. national parks in a time marked by barren budgets, rising energy cravings and warming skies.http://today.msnbc.msn.com/id/38883753/ns/travel-active_travel/

By Bill Briggs -- MSNBC.com Contributor

Environmental Sustainability
population growth