Atop this country's continental divide sits an outlook called la ventana, "the window" in Spanish. On clear days, visitors can see the Pacific Ocean to the west; by taking a few steps in the other direction, they can gaze at the foothills descending to the Caribbean plain to the east. A nearly constant easterly wind blows. The moisture it brings condenses at this near mile-high altitude, forming a thick mist that blankets the forest of gnarled, moss-covered trees.
Awestruck visitors inevitably use "fairy tale" to describe the view. But the enchantment belies a rapidly changing ecosystem. In the past 30 years, the weather here has changed. Average temperatures are higher. The clouds that define the forest now form farther up the mountain. More days pass without rain. And sometime between 1987 and 1988, the hottest year on record until then, two small inhabitants found only on this mountain – the golden toad and the Monteverde harlequin frog – disappeared.
One veteran scientist here calls it the first extinction caused by global warming.
Clad in khakis with a shaved head that only accentuates his striking white eyebrows, American ecologist Alan Pounds has walked Monteverde's trails for 26 years. He likes to joke: Should he enter a zero in his notebook ledger next to sightings for "golden toad"? But when he talks about what he's seen, he grows solemn.
"It's not the same place as it was before," says Dr. Pounds, the scientist-in-residence here at the Monteverde Cloud Forest Preserve. "It's disheartening to walk in the forest and know that you're not going to see harlequin frogs or golden toads.... We should be asking, 'Well, who's next?' "
The world saw a 1.4 degree F. increase in average temperatures during the past century. Two-thirds of that increase – 1 degree – occurred in the past 30 years. The vast majority of scientists say that human-emitted greenhouse gases are responsible for this warming trend. The Intergovernmental Panel on Climate Change (IPCC) predicts that even if some efforts are made to combat global warming, temperatures will rise another 5 degrees F. worldwide by century's end. If humanity does nothing, temperatures could rise 10 degrees F. or more.
As the globe warms, scientists foresee today's ecozones – distinct bands of habitat defined by temperature and rainfall – moving away from the equator and toward the poles, or upward toward the peaks in mountainous regions. In theory, wildlife could move along with these sliding zones. In fact, many species have already shifted from their former habitats.
But in a fragmented landscape with wildlife populations already weakened by other stresses – and with such a rapid rate of change – scientists worry that many plants and animals won't be able to adjust. Cities, cultivated fields, and other human obstacles may prove impassible for species run ragged by habitat loss and pollution.
Some 25 percent of all known species – plant and animal – could succumb to these combined stresses by century's end, according to the IPCC. So many species disappearing so quickly hasn't happened since an asteroid slammed into Earth 65 million years ago.
With mass extinctions in the making, scientists are scrambling for ways to lessen global warming's impact. They suggest giving wildlife space to adjust with "biological corridors," highways of nature that connect wilderness areas up mountains and across latitudes. They propose intentionally moving those species that may not be able to adjust fast enough. And they advocate captive breeding – or banking – of those species in immediate danger of disappearing.
The motives behind these efforts are not just altruistic. Losing any species could mean losing proteins and enzymes found nowhere else – substances of potential value to pharmaceutical companies. But in a broader sense, humans rely on functioning ecosystems for what scientists call "ecosystem services": Fresh water comes from forest-covered mountaintops, fish from healthy seas. Losing wildlife means pushing these systems closer to collapse.
"Ultimately you'll have ecosystems that just disassemble," says Thomas Lovejoy, president of the Heinz Center for Science, Economics, and the Environment in Washington, D.C. "And we've never lived in a world like that."
Many species have survived huge changes in Earth's climate over millions of years, leading some people to ask why species won't be able to simply adapt again.
But this time the warming is different, says Jack Williams, an assistant professor of geography at the University of Wisconsin at Madison.
All of human history has taken place during an "interglacial," a relatively warm period in Earth's climate cycle. Humans think that current conditions are the norm. But in fact, ice age conditions have persisted during 80 percent of the time since the most recent ice age cycle began 1.8 million years ago; only 10 to 20 percent of that time has been "normal," Dr. Williams says.
Because Earth is already in a warm period, still higher temperatures may push some wildlife off the map. "You can't just pick them up and plop them somewhere else," Williams says. "These climate zones will actually disappear from the entire globe by the end of the century."