Global warming is threatening to ruin many of America's most treasured national parks, including Yosemite, Yellowstone and Death Valley, environmental groups have warned. The risks include more forest fires, retreating snow lines, disappearing glaciers and the displacing of rare animal species.
"Rising temperatures, drought, wildfires and diminished snowfalls endanger wildlife and threaten hiking, fishing and other recreational activities," said Theo Spencer of the National Resources Defence Council. "Imagine Glacier Park without glaciers or Yellowstone without any grizzly bears."
The report, published jointly by the Defence Council and the Rocky Mountain Climate Organisation, lists 12 parks considered to be in greatest jeopardy from rising temperatures. All are in the western United States where average temperatures have risen twice as fast as elsewhere in the country.
By focusing on the dangers for the parks, the authors are hoping to recruit more members of the public into putting pressure on the US government to act on global warming. Most of the US is in the grip of an intense heat wave just as all the national parks are jammed for the summer holiday season.
Meanwhile, researchers at the National Climatic Data Centre in North Carolina recently reported that the first six months of this year were the hottest on record since 1895.
"If we continue to increase our emissions of heat-trapping gases, a disrupted climate will cause the greatest damage to our national parks ever," said Stephen Saunders, a co-author of the report and president of the Rocky Mountain Climate Organisation.
Among the dire predictions contained in the report, is the vision of familiar snowy peaks vanishing during the summer months from Mount Rainier National Park while lakes and streams in the Grand Teton and Rocky Mountain parks might soon dry up, frustrating fishermen and kayakers and driving animals in search of water elsewhere.
The report, which relies on global warming models and analyses from scientists at institutions such as the US Geological Survey and Nasa, suggests even the Joshua tree may be eliminated from Joshua Tree National Park and all the glaciers will be gone from Glacier National Park by 2030. At risk from rising sea levels are coastal parks such as the Golden Gate National Recreation Area in San Francisco.
"This is an across-the-board alarm that some of our most special places really are at risk," said Mr Spencer. "We need federal efforts to limit global warming pollution across the board. It's as simple as that."
Yosemite
Where is it? California
Annual number of visitors: 3.3 million
Famous for? Sequoias, mountains, waterfalls
How is it being affected? Main threat is forest fires. The acreage burned will rise by 50 per cent by 2050, thanks to rising temperatures and deepening drought. Meanwhile, Yosemite's glaciers are melting. They have already shrunk by between 31 per cent and 78 per cent in the past 100 years. Animals believed to be at risk include the diminutive pika, an alpine relative of the rabbit. Hikers used to see pikas at 7,500ft or above. Now they cannot be seen below 9,500ft as rising temperatures force them up the slopes. Soon, they will run out of mountain.
Worst case scenario? Alpine wildlife threatened, woodland destroyed by forest fires, glacial meltdown.
Glacier
Where is it? Montana
Annual number of visitors: 1.9 million
Famous for? Wildlife, spectacular deep valley glaciers, hanging valleys and glacial ridges
How is it being affected? Left to their own devices, glaciers shrink and expand over thousands of years. But recently, rising temperatures have sharply accelerated the melting process. All the ice formations in the park are now shrinking at an unprecedented rate. In 1968, there were 68 glaciers in the park. Today there are just 27. The park's signature turquoise lakes, yellow glacier lilies and alpine tundra will disappear with them. Visitor numbers are already dwindling; the park was once popular with cross-country skiers all year round.
Worst case scenario? Scientists expect all the glaciers in the park to have melted by 2030.
Grand Teton
Where is it? Wyoming
Annual number of visitors: 2.5 million
Famous for? Spectacular mountain scenery and wildlife ranging from bison to bald eagles
How is it being affected? Grand Teton National Park is one of America's busiest parks. Its popularity, however, is one of its drawbacks. The elk, moose, bison, grizzly bears, and hundreds of other species who thrive in this wild and desolate country, are having to compete for space and are drifting further afield in search of new pastures. As in Yellowstone (see above) climate change is allowing termites and insects to have an impact on many species of trees, posing a real threat to the sources of food on which the park's wildlife depends.
Worst case scenario? Wildlife extinction, overcrowding and changes in vegetation.
Glen Canyon
Where is it? Utah and Arizona
Annual number of visitors: 1.9 million
Famous for? Desert canyons, red limestone rock, watersports, rattlesnakes
How is it being affected? Years of drought caused the man-made Lake Powell to drop from full to 30 per cent capacity in 2005. Water levels could plummet by a further 30 per cent if climate change takes hold. As snow melts faster and rain falls in the place of snow, peak river flows could make white water rafting and kayaking too dangerous.
Worst case scenario? Drought, depleted tourist numbers.
Yellowstone
Where is it? Wyoming, Montana and Idaho
Annual number of visitors: 2.5-3 million
Famous for? Geothermal features and wildlife, including the largest population of grizzly bears in the US and the world's largest geyser. A third of Americans have visited Yellowstone.
How is it being affected? Hotter summers bring pest outbreaks, less snowfall and more intense wildfires, which threaten the iconic American wildlife so many tourists come to see. Although the population of grizzly bears, once endangered, is now slowly on the rise, park researchers say the bears are not out of the woods yet. Rising temperatures have left sources of food such as whitebark pine vulnerable to destructive insects that were previously repelled by cold temperatures. Grizzlies are already venturing further from their territory in an attempt to locate food; encounters with trigger-happy humans are the top threat to the species' survival.
Worst case scenario? More wildfires, melting snow, no more grizzlies.
Death Valley
Where is it? California
Annual number of visitors: 800,000
Famous for? Intense heat, sand dunes, canyons, haunting sunsets, abandoned mining towns
How is it being affected? Death Valley is often held up as an example of what will happen to the rest of the world if we do not heed the warning signs of climate change. But it too will suffer. Death Valley is a sensitive environment that straddles a fault line. Its sub-alpine pine forest will wither, stronger winds will cause more intense sandstorms, blasting geomorphic rock structures and causing frequent volcanic eruptions. The already intense heat will become intolerable, killing what little wildlife inhabits the area.
Worst case scenario? Nothing - not even mountain lions and kangaroo rats - will survive.
Golden Gate
Where is it? California
Annual number of visitors: 13.6 million
Famous for? Sprawling sandy beaches, bison and as a weekend escape for millions of San Franciscans
How is it being affected? The remit for the Golden Gate park, when it was established in 1972 on the outskirts of San Francisco, was to "bring parks to the people". But "the people" will have a battle on their hands if sea levels rise, depriving seven million Bay Area dwellers of cherished broad beaches and sweeping cliffs. A sea level increase of three feet would inundate all the sandy beaches in the Golden Gate National Recreation Area.
Worst case scenario? Erosion of cliff faces and loss of all sandy beaches, used by more than seven million people a year.
Mount Rainier
Where is it? Washington State
Annual number of visitors: 1.2 million
Famous for? Active volcano and 97 per cent designated wilderness
How is it being affected? Established in 1899, Mount Rainier National Park covers a desolate 236,000 acres with an active volcano encased in more than 35 square miles of ice and snow. A decrease in the volume of snowfall due to global warming will lead the park's most visited spot - Paradise Valley, an awe-inspiring expanse of meadows carpeted with brilliantly coloured wildflowers - to disappear. Warmer climes will result in trees dominating the meadows, preventing wild flowers from growing and depriving the area of its magnificent colour.
Worst case scenario? Loss of wildflower meadows and recession of glaciers.
Rocky Mountain
Where is it? Colorado
Annual number of visitors: 2.7 million
Famous for? High mountain passes, climbing, wildlife
How is it being affected? Above the tree line in Colorado, this park boasts the biggest expanse of alpine tundra in the lower 48 states. Very high snowfall, screaming winds and a very short growing season already create an environment too hostile for trees to take root. But with rising temperatures, trees are creeping into the area, spelling an eventual end to the tundra. For every degree of warming, the trees could climb another 250 feet. If average temperatures were to rise by 9C, the tundra, with its unusual flower and birdlife, could be gone altogether.
Worst case scenario? Loss of rare plant and wildlife species, dwindling tourist numbers.
Bandelier
Where is it? New Mexico
Annual number of visitors: 250,000
Famous for? Wildflowers, trees, ice formations, climbing.
How is it being affected? In the searing New Mexico heat, the forests of Bandelier National Park offer precious relief. Rising temperatures could destroy much of the woodland, leaving wildlife and plants exposed. In 2002-03, extreme temperatures helped the natural destruction of vast expanses of the low-elevation forests that ring the park. In one area, 90 per cent of piñon trees died. There are no signs of regrowth. Botanists suspect this may be a repeat of the 1950 drought which killed whole forests of ponderosa trees.
Worst case scenario? Permanent loss of natural forests, woodland and animal life, including Pacific jumping mice.
North Cascades
Where is it? Washington State
Annual number of visitors: 18,500
Famous for? Cascading waterfalls and its status as the most heavily glaciated area in the United States outside of Alaska.
How is it being affected? The glaciers responsible for the park's chiselled peaks and tumbling streams are particularly vulnerable to changes in temperature and precipitation, making them important indicators of climate change. Experts say they are receding fast. Since 1959 they have lost more thanr 80 per cent of their ice, leading to summer streams being reduced by 30 per cent. Already threatened by over-fishing, salmon will be particularly vulnerable as they search for cold water streams.
Worst case scenario? Complete loss of glaciers leading to extinction of river species.
Mesa Verde
Where is it? Colorado
Famous for? More than 4,000 archaeological sites dating from AD600 and the stone "cliff dwellings" of the ancestral Pueblo people.
How is it being affected? More than half of the piñon trees at Mesa Verde National Park died from soaring temperatures between 2000 and 2003. Heat and drought threaten to destroy the habitats of the mountain lions, coyotes and blankets of richly coloured wildflowers that decorate the Colorado Plateau. Extreme temperatures in the arid area threaten to repel visitors, as well as archaeologists studying the site.
Worst case scenario? Baking temperatures, droughts and floods caused by global warming could eradicate plantlife, obliterate historical artefacts and terminate archaeological investigations.