Nature lovers flock to our national parks to experience the natural beauty and fresh air of the great outdoors. But according to the National Parks Conservation Association, some of Americas most iconic landscapes are under threat from air pollution and climate change. These threats can weaken the health of plants and animals and can permanently harm ecosystems. Pollution can also affect visitors health and enjoyment. In a new report, the NPCA has revealed the most polluted national parks in the U.S.

　　Topping the list of the most polluted parks in the U.S. are four parks in California: Sequoia Kings, Joshua Tree, Mojave and Yosemite. The pollution at Sequoia Kings raises significant concerns about visibility, health and nature. Joshua Tree and Mojave both have consistently unhealthy air that is harmful to visitors and rangers. All four California parks face climate change threats from wildfires, drought and invasive species. Oil and gas, agricultural operations and vehicle traffic across the Golden State result in poor visibility and dirty air.

　　"With stunning mountains, caverns, forests, foothills and 2,000-plus-year-old sequoias towering overhead, the Land of Giants might seem invincible. In truth, these majestic parks, and the plants and wildlife, which rely on them, face the unique and devastating consequences from human-caused air pollution and climate change," the report said.

　　According to the report, 97 percent of national parks suffer from significant or unsatisfactory air pollution levels and 98 percent suffer from haze pollution. The other U.S. parks on the top ten most polluted list are Carlsbad Caverns National Park in New Mexico, Death Valley National Park in California, Indiana Dunes National Park in Indiana, Guadalupe Mountains National Park in Texas, Rocky Mountain National Park in Colorado and White Sands National Park in New Mexico.

　　"Air pollution and climate change remain some of the most serious threats to the health of our parks todayand the problems they cause include weakening the health of plants and animals, permanently harming ecosystems and negatively affecting visitors health and enjoyment," the report said.

　　Read the full report here.