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In 1975, the Brazilian scientist Enéas Salati made an astonishing discovery: the Amazon rainforest doesn’t just receive an unusual level of precipitation but actually creates half its own rainfall. The moisture contained in air masses crossing the Amazon basin, he showed, cycles through five or six phases of precipitation and evaporation before it reaches the high wall of the Andes Mountains. There, it rises, cools, and rains down one last time in a mighty deluge that suffuses the Amazon River system with water.
Previously, scientists had regarded vegetation largely as a consequence of climate. Forests, they believed, responded to their climatic environments but didn’t actively shape them. Salati showed to what extent plants and soil hold water and distribute it across large, evaporative surfaces—leaves, in particular—powering a hydrologic cycle that sustains the rainforest climate. His findings raised the possibility that deforestation might eventually degrade the hydrologic cycle to such an extent that the region’s climate would change. And in the decades after his study, as development and deforestation ravaged huge swaths of the jungle, scientists concluded that there is in fact a tipping point after which the Amazon will no longer generate sufficient rainfall to maintain forest cover in much of its southern and eastern regions.
That tipping point is now at hand. Approximately 20 percent of the Brazilian Amazon has been stripped of its trees, and the Brazilian government’s recent rollback of rainforest-protection laws and programs has accelerated the pace of environmental destruction. Between July 2018 and July 2019, deforestation in the Brazilian Amazon soared to an 11-year high—wiping out a total of 3,789 square miles of forest, an area larger than Yellowstone National Park in the United States. But the problem goes beyond Brazil. Colombia, Peru, Venezuela, and other countries that extend into the Amazon have deforestation problems, as well. Unless governments across South America join together to protect the vast rainforest ecosystem, its southern and eastern regions will eventually turn into a grassland savanna. The result will be a tremendous loss of biodiversity and economic potential that will undercut agriculture and power production across much of South America and upend the lives of millions of people.
The Amazon River basin spans six countries and covers more than a third of the South American continent. It contains roughly 20 percent of the world’s river water and generates electricity and irrigates crops across much of South America. With the exception of Chile, every South American country benefits directly from the Amazon’s moisture. Its unique hydrology makes central Brazilian agriculture possible and helps keep the lights on from São Paulo to Rio de Janeiro.
But over the past five decades, deforestation has destabilized the unique ecosystem that underpins this prosperity. Most development plans for the Amazon were drawn up when the region’s hydrologic cycle was still poorly understood. More often than not, such plans were designed to extend the reach of government into the Amazon and didn’t take into account the region’s ecological needs. Consider, for example, the Belém-Brasília Highway, the first road from the northeastern coast of Brazil to the country’s capital in the interior, which was completed in 1960. The roadway’s planners didn’t expect that impoverished Brazilians from the arid northeast and the populous south would colonize the roadside, tearing down the forest in search of short-term economic opportunities. But come they did, building settlements and ranches and swelling the populations of cities in the Amazon, such as Araguaína and Imperatriz. In the 1980s, history repeated itself: after the completion of BR-364—the highway connecting the southern state of São Paulo to the northwestern state of Acre—hundreds of thousands of migrants settled along the route in the state of Rondônia, which has since been substantially deforested. The problem has repeated itself with every highway project since.
Large-scale hydropower projects have also damaged the Amazon River basin’s ecology. The region’s rivers carry huge sediment loads from the Andes Mountains. Conventional dam designs block those flows, stripping the water of nutrients and harming riverine flora and fauna. Dams further disrupt the hydrologic cycle by turning large tracts of forest into reservoirs.
But by far the most disruptive developments have been human settlements. Made possible by the network of roads and highways constructed over the last 60 years, cities now dot much of the Amazonian heartland. Most are small and densely populated, but some, such as Manaus and Belém, are large even by non-Amazonian standards. People have also settled in rural areas of the Amazon basin to raise livestock and cultivate soybeans and other crops. These agriculturists and ranchers often cut down trees or burn them to enable planting or grazing. Under Brazilian law, landowners can legally clear up to 20 percent of their forested land, but many disregard the law and clear much more than that. Between 1990 and 2005, around 80 percent of deforestation in the Brazilian Amazon was attributable to ranching.
South American governments must reconsider their approach to development in the Amazon. Infrastructure projects, for instance, would be more effective and sustainable if they embraced the traditional and less expensive transport system of the region—the rivers. Ships can travel from Brazil’s northeastern Atlantic coast all the way to Peru and Colombia on the Amazon and its tributaries. Some of the rivers may need minor adjustments to make them navigable, but they require far less investment than do roads and can ferry comparable numbers of people. Additional highway systems, to the extent that they are necessary, should be elevated above the jungle so that they can’t be easily colonized in the way that previous road developments have been. Elevated highways would be more expensive to construct but far less costly to maintain, resulting in net savings over time.
Governments must also rethink their hydropower projects. Instead of building additional conventional dams, they should opt for run-of-river designs—such as the Teles Pires dam in Brazil—that let sediments flow freely and don’t interrupt the migration of river life. Solar power could also fulfill some of the energy needs currently met by hydropower; the sun is strong enough at the equator to generate power even on cloudy days. Solar farms could be built atop already deforested areas, eliminating the need to clear additional forestlands. At the same time, governments could promote the use of rooftop solar panels in rainforest cities and towns, enabling the Amazon to meet most of its internal energy needs from solar power alone.
Forest cover in Brazil is especially important, since the hydrologic cycle starts in that country.
Finally, South American governments must adopt a more sustainable approach to the settlement of the rainforest. While far from perfect, the city of Manaus in the Brazilian state of Amazonas is a useful model: the city of 2.5 million people is sustained largely by industries that don’t draw on raw materials from the forest. As a result, Manaus’s economy has been able to grow even as the rate of deforestation in the state of Amazonas has declined.
But sustainable development projects can go only so far. The hydrologic cycle won’t stabilize until forest cover returns to sizable portions of the Amazon River basin. (Forest cover in Brazil is especially important, since the hydrologic cycle starts in that country.) As a result, governments in the region will have to reforest significant tracts of land. Brazil made meaningful reforestation pledges as part of the 2016 Paris agreement on climate change—concessions that, if implemented, could help shore up the region’s weakened hydrological cycle.
One policy that could help bring the region’s fragile ecosystem back into equilibrium would involve reforesting three acres of land for every one acre that is cleared for (legal or illegal) development. A three-to-one ratio is necessary, as climate scientist Carlos Nobre and I have argued, because deforested land contributes relatively little to the hydrologic cycle and makes only a small contribution during the early stages of reforestation. Such a policy would allow for limited legal deforestation at the same time that governments increase forest cover, fortifying the hydrologic cycle so that the Amazon can continue to feed and power much of South America.
Unfortunately, some governments in the region are doing the opposite, accelerating the pace of deforestation and doing little to replenish the jungle. Brazilian President Jair Bolsonaro, in particular, has pursued outmoded development initiatives. In late 2019, Bolsonaro announced a measure that would grant legal land titles to irregular occupants in the Amazon, enabling them to get bank credit on their properties and to reside without fear of eviction. Without amendments to prevent additional land from being cleared, however, this policy will only reward past illegal behavior and incentivize further deforestation.
As the country whose share of the Amazon basin is the largest, Brazil must lead the charge to protect the rainforest ecosystem. The country is well positioned to do so, with one of the best scientific establishments in the world. And to a far greater extent than Bolivia or Ecuador, Brazil boasts a population that is largely conscious of and concerned about the environment. The Brazilian government should capitalize on popular support for environmental initiatives to pursue a policy of forest stewardship. Where Brazil leads, other countries in the region will follow.