The prospect of collapse is forcing a profound change in environmental thinking. Not long ago, those who lobbied for the rain forests did so on the earnest but limited argument that biodiversity was at risk. Conservation groups raised funds to rescue imperiled species, like the jaguar or the blue macaw, and pressured governments to stop razing ecological “hot spots.” Climate change has widened the focus. The ecological hot spot today is the biosphere. “The loss of biodiversity and the composition of landscapes are important, but as symptoms, not determinants of life on this planet,” says Nepstad. “It’s the big cycles that are running the show, and that’s where the rain forests come in.”
Too much carbon in the air could also pose a double threat. At first, the forests may flourish; since plants need carbon to grow, processing it into life-giving sugars and chemicals through photosynthesis, the extra dose of CO2 will jolt them into overdrive. “But the forest cannot expand forever,” says Scott Lewis, a scientist at Leeds University. Eventually, the overworked machinery of trees will fail, along with the nutrients in the soils. Trees sated with carbon also tend to shut down their stomates, tiny pores on the leaves that take in CO2 and exhale oxygen and water vapor— leading to even drier forests.
The experts will surely continue to quibble over the details, but no one doubts anymore that keeping the planet habitable will be a lot easier with the rain forests than without them.
