From a 13,000-foot peak of the Andes Mountains in southern Peru, gazing east over the dense rain forests of the Amazon basin, all you see is undulating green—one of the most verdant places on the planet.
It's what you can't see that matters.
The plants are on the run, trying to move to higher ground, where the air is cool enough to support their existence.
"Most of these species are not going to be able to tolerate climate change," says Ken Feeley, a tropical biologist from Florida International University in Miami, "mostly because climate change is happening so fast."
Feeley spoke as we hiked into the jungle with a small group of other scientists—through an area that contains more tree, plant, bird, and animal species than the entire eastern seaboard of the United States.
It is here that an international collective of scientists, called the Andes Biodiversity and Ecosystem Research Group, has mapped one of the largest field grids of its kind for a wide range of climate change studies.
According to a decade of research by Feeley and his colleagues, including tropical biologist Miles Silman of Wake Forest University, tropical species are frantically migrating upslope as they reproduce. But they may not be moving fast enough.
Tropical Andean tree species are shifting roughly 8 to 12 vertical feet (2.5 to 3.5 meters) a year on average—the arboreal equivalent of a dash. Yet for those trees to remain in equilibrium with their preferred temperatures, they need to migrate more than 20 vertical feet a year.
"We are looking at what entire populations of these species are doing in response to climate change," Silman said. "It's fairly spectacular and quick. But it might not be quick enough."
As we hike, I notice a large, bushy schefflera with umbrella-like leaves. It looks just like the one I have in a pot on my porch back home in North Carolina. Silman says it could survive the race. Of 38 species tracked in the 2010 study, schefflera is migrating the fastest, as much as a hundred vertical feet a year. But ficus, another common houseplant native to the tropics, could be doomed. It is migrating less than five vertical feet annually.
Research models by other biologists project that more than 50 percent of tropical species could die off by 2100 or sooner if average temperatures rise by 7 degrees Fahrenheit, as climate experts predict. If the planet warms even more, which is possible, extinctions could reach 90 percent.
"Particle Accelerator of Tropical Biology"
When ice caps melt, it is relatively easy for scientists to describe what is going on—and calving glaciers make for dramatic images. But the tropics are difficult to access, and are less well understood.
For the past decade, however, the Andes Group has been helping to fill the relative research vacuum. The scientists, including co-founder Silman, are from the United Kingdom, the United States, and Peru.
They use an ancient, rock-strewn Incan trail, the Troucha Union, for access to their study field. After ascending a series of switchbacks on a six-hour ride from Cuzco, the trail starts at 13,000 feet in the southernmost part of Manú National Park. It then winds and drops deep into the Amazon basin.
The research plots initially consisted of eight one-hectare squares (110 yards by 110 yards) and now number more than 20. Each of the higher plots is separated by about 800 feet of vertical elevation. Because of the changes in elevation, the temperature between plots differs by about 2 degrees Fahrenheit.
As a result, species change from plot to plot too: Between plot one at 11,320 feet and plot four at 8,860 feet, for example, there is about a 90 percent differentiation in species. There are no species in common between plot one at the top and plot eight at 5,905 feet.
The boundaries—delineated with bright plastic tape—were installed in 2003 by Silman with assistance from a group of hardy Peruvian graduate students. Each of the plots is a chaotic morass of trees covered with epiphytes and vines; some are on sheer slopes with precipitous drop-offs.
"Tropical regions are understudied because they have been mostly inaccessible to science," Greg Asner, a biologist with the Carnegie Institute for Science at Stanford, told me during a conference of the Andes Group in Pisac, a village in Peru's Sacred Valley not far from Machu Picchu. "On the ground, where there is only difficult terrain or rough jungle, it's famously difficult to access."
The Peruvians visit the area several times a year to gather data on the growth patterns of trees inside the taped boundaries; the statistical analyses of that data led to the tree-migration findings.
"Miles's initial vision for the plots as an open-source research tool for our field has really come to fruition,"Brian Enquist, an ecologist and evolutionary biologist from the University of Arizona, told me. "Those plots are to tropical biologists what the particle accelerator has been to physicists."
Many biological and climate studies are underway here. Yadvinder Malhi of Oxford University and Patrick Meir of the University of Edinburgh use the plots to study how carbon is absorbed and converted into plant tissue in the process of photosynthesis. Asner uses infrared lasers to examine the area from a high-tech plane called the Carnegie Airborne Observatory. Other scientists are studying the soil, the insects, the ferns, and the frogs, which are dying off. The San Diego Zoo has been invited to join the Andes Group to study animals in the area.
Small Changes, Big Implications
In two weeks of interviews with biologists—while hiking through the Andes or meeting between lectures in Pisac—I heard dire concerns not only about biodiversity, but also about impacts on natural systems that regulate temperature and weather patterns around the world.
"Small changes in the tropics can have huge ramifications for the entire Earth system," Malhi of Oxford told me. "Changes in rainfall in the Amazon, for example, feed forward to changes in rainfall in North America and Europe and in central Asia."
It's the sheer size and intensity of what happens in the tropics that makes the impact so alarming. Greenhouse gases are absorbed and stored as biomass in the trunks, limbs, and roots of tropical trees. Water pulled from the oceans cycles through the trees and then exits as moisture that turns into the clouds that help cool the Earth or deliver rain.
It's easy to see how degraded or reduced tropical forests could mean less greenhouse gas being absorbed and fewer clouds being produced. Under that scenario, global warming could accelerate, the scientists fear, and less rainfall could make raising crops more difficult where populations are growing the fastest.
The Conservation Challenge
What can be done? Many of the tropical biologists I interviewed in Peru argue that the United States and China, which account for more than 40 percent of greenhouse gases, must implement sweeping policies to reduce those emissions significantly. Plus, the scientists say, poorer countries rich in tropical forests like Peru, Ecuador, and Indonesia will need lucrative financial incentives from wealthy countries to preserve and protect those forests, instead of mining or drilling for the natural resources beneath them.
"If you have so many billion tons of carbon stored in your forests, that becomes an asset like Saudi Arabia's oil money," said Sassan Saatchi, a senior scientist with NASA's Jet Propulsion Laboratory at the California Institute of Technology.
The idea of carbon offsets, promoted by the United Nations since 2009, is promising. But it's been slow to catch on. Ecuador, for example, recently requested $3.6 billion from developed countries to set aside 4,000 square miles of rain forest. Virtually no investors stepped forward. The president of Ecuador pledged to drill for Amazonian oil instead.