So much of the world is covered with roads, houses, buildings and crops that America's wilderness areas and national parks have become scientific laboratories that show how the natural world is changing and offer lessons for policy makers. For example, scientists in Glacier National Park, in the northwestern state of Montana, are adding evidence to the debate over global warming. They say the park's glaciers are melting away.
Glaciers are huge chunks of ice so heavy that they move slowly downhill, crunching, pounding and shaping the landscape as they go. But that may no longer happen here in northwest Montana, where glaciers were once so big Congress preserved the place as Glacier National Park.
"We're looking out across the park toward one of the larger remaining glaciers, Jackson Glacier," Brian Peck of the Sierra Club says.
He leans on a park road sign and surveys the ice field glistening in front of him. "Like all the glaciers up here, even though it's one of the bigger ones, it's shrunk probably two-thirds since 1850," Mr. Peck says.
In 1850, there were 150 glaciers in the park. A century later, there were only 37, and there are even fewer today, according to Glacier National Park ecologist Daniel Fagre. As he gathers data for a new inventory of the remaining glaciers, he blames global warming for their disappearance.
"They are not getting enough snow during the winter to keep feeding the ice that is melting in the summer," Mr. Fagre says.
That is changing the nature of Glacier National Park, and affecting the plants and animals that live here.
"We're going to eventually lose our alpine tundra areas, they're going to fill in with trees - these have much of the plant biodiversity for this park. This is the upper area where a lot of those flowers that are charismatic are, where people like to take pictures. It's also where the big horn sheep reside. They are not good at eating trees, so big horn sheep habitat will go down," he says.
Grizzly bear habitat will diminish too, as mountaintops grow warmer. Park wildlife biologist Kate Kendell explains that each summer, army cutworm moths fly to alpine meadows where grizzly bears feast on them.
"They can consume up to 40,000 moths a day on these sites which is 20,000 calories. It's a big deal for these bears and the army cutworm moths are there because they cannot tolerate high temperatures of the lower elevations during the summer, so those could be affected by some sort of climate change," she says.
Outside the park, people will be affected by the warming of the planet as well. Scientists predict oceans could rise between 23 and 46 centimeters over the next century, drowning small, inhabited Pacific Islands. Even communities far from the world's oceans could disappear. Ecologist Daniel Fagre warns that if glaciers melt away, some mountain villages in Asia will eventually go dry.
"There are places in the Himalayas where all of the water sources come from glaciers and melting glaciers. And there are irrigation systems, entire valleys with a number of towns in them, will have no water source, because it's a very arid area," he says.
He says this isn't the first time the earth has experienced global warming. "But what is different about this is, it is so rapid. So we are seeing a change in just a few decades that used to take hundreds of years," Mr. Fagre says.
That means plants, animals and even people have little time to adapt to all the changes. And perhaps even less time to try to reverse them.