When even the South Pole gets tourists, the remotest regions on Earth can seem accessible to anyone with a credit card. Yet the world's tropical rain forests remain places of profound mystery. Scientists estimate that millions of the species that live within these lush expanses have yet to be observed and classified by biological taxonomists. At the same time, organizations that work to protect the rights of indigenous peoples attest that some tribes living deep within rain forests have had little-if any-contact with the outside world.

The remoteness of the rain forests, however, has not proved sufficient protection from a number of formidable encroaching forces: Oil exploration; deforestation fueled by the world's hunger for cheap soybean and palm oils, timber, and beef; and the effects of global warming all threaten the future of these diverse and invaluable natural resources.

As the race to stop global warming gains speed, billions of people around the world who have never set foot under a tropical canopy may soon find that they, too, are more dependent on rain forests than they might have realized-and not just for cheap commodities. Stopping or at least slowing deforestation can in turn help lessen the pace of the rise in global temperatures. Indeed, saving the rain forests is no longer just about preserving habitats for the endangered red-backed squirrel monkey and its canopy-dwelling brethren. It could mean saving the habitat that the rest of us live in, too.

The effort to preserve the world's remaining tropical rain forests spans across countries and continents-from the Amazon Basin (including parts of Brazil, Ecuador, Peru, and Bolivia) to Indonesia and Malaysia (especially the island of Borneo), as well as Papua New Guinea, the Democratic Republic of Congo, and Cameroon. Here's a glimpse of what's at stake.

How much of the tropical rain forest is already gone?
About 15 percent of the land on Earth was once covered by tropical rain forest. Today more than half of that has already been lost, with just 7 percent of the terrestrial Earth still under a rain-forest canopy, according to data from the World Wildlife Fund.

Alas, that doesn't mean that the remaining rain forest is pristine habitat. A recent analysis of satellite photos of the Brazilian Amazon by ecologists at Stanford University revealed that the forest there had suffered selective logging (a procedure in which commercially valuable trees are individually extracted) at twice the rate scientists had previously predicted. If such logging is done illegally and unsustainably (as it is in many cases), it can leave the remaining forest less biologically productive, more vulnerable to wildfires, and marred by roads, all factors that lead to further environmental degradation.

Global warming as well is starting to change the forests. To take just one example: Scientists have observed large trees in the Amazon growing at a faster rate over the past two decades, while smaller trees have begun to lag. Their hypothesis is that the increased amount of carbon dioxide (CO2) in the atmosphere is essentially fertilizing the rain forest. In the increasing competition for sunlight, water, and nutrients in the soil, the big trees are winning, while the small trees are losing out. Such subtle changes in the forests' ecology could disrupt their fragile balance, endangering rare plants and animals.

What are the greatest threats to rain forests today?
The chief threat is the clearing of land-either by burning or by clear-cutting-in order to grow crops to produce soybean oil and palm oil. Soybean oil, the world's most widely used edible oil, is found in margarine, shortening, and meat substitutes. Palm oil, the world's second most popular edible oil, is used in cookies, crackers, toothpaste, bread, and ice cream.

In 2006, soy production overtook cattle ranching and logging as the greatest cause of rain-forest destruction in the Amazon. In that same year, agribusiness giants Cargill and Archer Daniels Midland agreed to a moratorium on buying soybeans from recently deforested areas for two years, while trying to work out a conservation deal with the Brazilian government and environmental groups. But the negotiations aren't going so well; this spring, Brazilian federal agents shut down a Cargill soy-export terminal.

In Malaysia and Indonesia, which produce 83 percent of the world's palm oil, growers are finding new demand for their crops-ironically, from the world's automobile drivers, many of whom are seeking "green" alternatives to fossil fuels. Conservationists have dubbed biofuel derived from palm-oil "deforestation diesel," because they don't want to see more rain forests lost to make way to grow crops for this supposedly green fuel.

What lives in the rain forest?
The rain forest is the most diverse habitat on Earth. Some 50 percent of the 1.8 million known species in the world live in tropical rain forests, including such charismatic Amazonian critters as the red howler monkey, the jaguar, and the world's largest rodent, the capybara.

But what's truly staggering is the number of still-unclassified species that scientists suspect lurk there. In early '80s, entomologist Terry Erwin of the Smithsonian Institution found 1,200 different kinds of insects living on just 19 specimens of a single tree species in the tropical forest in Panama-leading him to the controversial estimation that the world at large may contain as many as 30 million species. Today, estimates of the number of species on Earth range widely from 10 million to 100 million, including bacteria and fungi, with many of those making their home in rain forests.

Who depends on rain forests?
Indirectly, we all depend on them. But for the 50 million or so indigenous people who live in tropical rain forests around the world, the connection is much more vital and direct: They rely on the forests for virtually all their food, fuel, and shelter. As recently as May 2007, a tribe whose 87 members have had very little contact with the outside world was located in a remote part of the Brazilian Amazon. The indigenous-rights group Survival International estimates that there may be as many as 100 similar tribes around the world-many of them in Papua New Guinea and Brazil-whose members choose to remain separate from the rest of civilization.

A significant threat to these peoples are the roads created by illegal logging and oil exploration, which bring a tide of colonists into previously inaccessible sections of the forest. These newcomers not only damage the land by not living sustainably but also bring diseases previously unknown to the isolated tribes.

The rain forest also regulates rainfall and protects watersheds important to many millions more who live outside it. When the forest cover is destroyed, the rain carries soil, agricultural chemicals, and garbage into rivers, polluting drinking water. What's more, large numbers of people die every year in tropical countries because of flooding and mudslides due to deforestation.

For many of the world's poor, the forest is also a kind of insurance policy. Some 40 percent of homes around the world are still heated by firewood, according to M. Sanjayan, lead scientist at the Nature Conservancy. "For a poor person living on the edge of a forest, that forest is their safety net," he says. "That's their Social Security check."

What do rain forests have to do with global warming?
Think of a healthy forest as a giant carbon sink. Leaves suck up carbon dioxide from the atmosphere through photosynthesis, converting the carbon into wood and other biomass, while releasing oxygen. But when a rain forest is burned to clear the land for agriculture or cattle ranching, much of the carbon that had been sequestered is released back into the atmosphere, contributing to global warming.

How big a problem is it?
In the next 24 hours, deforestation will release as much CO2 into the atmosphere as 8 million people flying from London to New York, according to Cool Earth, an organization working to preserve the rain forests and so fight climate change.

Each year deforestation, much of it inflicted on rain forests, accounts for almost 20 percent of all the greenhouse gases caused by human activity. That makes it second only to power generation as the world's largest human-caused source of greenhouse gas emissions. Deforestation is a bigger source of these gases than driving cars and air travel combined. In fact, if deforestation continues unabated at its current rate, over the next five years it will generate emissions greater than what will have been produced by all aircraft from the beginning of flight through 2025, according to the Global Canopy Programme, a consortium of rain-forest scientists from around the world.

Indonesia is the third largest emitter of greenhouse gases in the world (behind China and the United States), with a whopping 85 percent of those emissions coming from deforestation. In Brazil, loss of forests accounts for some 70 percent of greenhouse gas emissions, making that country the fourth largest emitter.

What can the rest of the world do about it?
Many developing countries see global warming as a problem caused by rich, industrialized nations-which, incidentally already cut down their own forests years ago and now scold poorer countries for destroying theirs. Scientists with the Global Canopy Programme believe that the best hope for saving the remaining rain forests is to create financial incentives for developing countries to do so, through international climate treaties.

"Curiously, climate change may end up giving these forests their best chance for survival," says Andrew Mitchell, executive director of Global Canopy. "Those countries wise enough to have retained their forests could find themselves the owners of the new billion-dollar ecosystem industries of the future." Under current treaties, such as the Kyoto Protocol, this hasn't happened yet, as forests have been left out of the greenhouse gas reduction schemes.

However, there are some projects, spearheaded by non-governmental organizations, that aim to protect forests in the name of fighting climate change. The Nature Conservancy, working with the government of Bolivia, has raised money from three U.S. energy companies to help preserve 1.5 million acres of rain forest in Noel Kempff Mercado National Park. The project is expected to avert the release of 17.8 million tons of carbon into the atmosphere by the prevention of logging and the conversion of land to agricultural uses. Cool Earth, a new organization endorsed by former British Prime Minister Tony Blair, encourages individuals and businesses to sponsor acres of rain forest in Brazil and Ecuador to fight climate change, and then to "visit" their patch of forest through Google Maps. The group's aim: price deforestation out of the market.

What else can consumers in developed nations do?
Whenever you buy sawn timber or products made from tropical wood, look for the Forest Stewardship Council label, which guarantees that the wood was harvested sustainably, without harming ecosystems or local communities. Home Depot now tracks individual trees with a bar code all the way from timber in the forest to processed lumber in the showroom. "It reduces the amount of illegal logging," says the Nature Conservancy's Sanjayan. "I guarantee if there is more consumer interest, more companies will do it."

It's harder to know where your soy- and palm-oil-based products come from, but some companies, such as the Body Shop and Unilever, are seeking out more sustainable alternatives. And when shopping for environmentally friendly food products such as coffee and chocolate, look for the Rainforest Alliance's green frog seal.

Can visiting a rain forest help?
Yes, but it depends on how you do it. Eco-travelers who flock to rain forests to see red-and-green macaws congregating at a clay lick, or to marvel at a caiman basking on a sandbar, create a big incentive for tropical countries to conserve rain forests.

But while vacationers prove with their dollars that a protected forest rich with native wildlife has economic value, not all lodges and tours are created equal. Before you book, be sure to research their environmental policies. The Rainforest Alliance suggests asking these ten questions before you make a reservation for a rain forest adventure.

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