Threat: Massive sheets of ice are breaking off the southern continent and floating out to sea. About 75 percent more ice was lost in 2006 than a decade earlier.
Consequence: As it melts, Antarctica's ice raises oceans worldwide, and there's a lot of it left to go: The continent's ice sheet averages over 7,000 feet thick.
Threat: The islands that inspired Darwin's theory of evolution draw some 120,000 tourists per year—and all sorts of traffic, development, and related activity. Invasive species, including feral goats, also threaten unique native wildlife.
Solutions: Tourists are carefully monitored and allowed at just a handful of sites throughout the islands. Unwelcome species are tracked and eradicated whenever possible.
The Everglades, Florida
Threat: The marshes, lakes, swamps, and pinelands that cover a vast stretch of southern Florida have been shaped by human hands for decades. Canals and levees add to the threats posed by encroaching urban development and agriculture.
Solution: The Comprehensive Everglades Restoration Plan, begun in 2000, is the biggest restoration project in history. At a cost of $10 billion so far, it attempts to control floods and also protect priceless native ecosystems.
Threat: Hemingway called the peak's snows "as wide as all the world." But that glacial cap could vanish completely in 15 years.
Consequence: Ice cores taken from the glaciers provide a unique climate record. If they melt, a natural scientific archive will be goneforever.
The Virungas, East Africa
Threat: In the jungles on these volcanic peaks, poaching and warfare stalk the rare mountain gorilla.
Solution: Carefully regulated gorilla tourism in Rwanda and Uganda has turned conservation into a cash crop.
Threat: A combination of ground subsidence and increasingly severe storms already floods this unique architectural treasure dozens of times a year. Rising sea levels could finish the job.
Solution: The Italian government hopes a $7 billion system of movable floodgates nicknamed "Moses," to be finished in 2012, will keep the hungry sea at bay long enough to find a more permanent solution.