By Chris Lang
A recent paper in the journal Environment: Science and Policy for Sustainable Development predicts that vast areas of the Amazon could reach a tipping point as soon as 2064. Needless to say, this is bad news.
The Amazon tipping point occurs when the rainforest can no longer support itself, for example when the forest needs four years to recover from drought but droughts happen every year.
The paper, titled, “Collision Course: Development Pushes Amazonia Toward Its Tipping Point,” is written by Robert Walker, a professor at the University of Florida. Walker describes himself as a quantitative economic geographer, whose research focusses on land cover change processes, especially tropical deforestation.
Walker writes,
A tipping point transgression would be disastrous for more than a tropical forest and its dependent ecosystems. Dependent human systems also would suffer greatly, and these systems lie not just within the Basin’s boundaries but also far beyond them.
Amazon tipping point
Since the Brazilian Amazon was opened up in the 1970s, about 20% has been deforested. Walker notes that Brazil managed to reduce deforestation between 2004 and 2012. But he adds that,
A generalized collapse of environmental governance in Brazil and other Amazonian nations has renewed public concerns about the fate of the forest. These concerns — recently intensified by Amazonian fires in the summer of 2019 — have put the focus on regional climate changes capable of inducing a “tipping point” beyond which the moist forest transitions to a tropical savanna. This could happen in a number of ways but would probably include some combination of changes in average annual precipitation and dry-season intensity.
Hydroclimate
The hydroclimate has also changed, with more rain falling in the wet season, and less in the dry season. The number of dry days has increased in both seasons. Since the 1980s, the dry season has lengthened. Severe droughts and floods are more frequent.
Between 2000 and 2012, the amount of rainfall has declined in the south and southeast of Brazil’s Amazon by one quarter. In the southeastern Amazon, in the same period, temperatures increased by more than 1.0°C.
Walker writes that,
Because its precipitation comes primarily from local convection, southern Amazonia’s rainfall is highly sensitive to land cover change, making it potentially more vulnerable to tipping point dynamics than elsewhere in the Basin.
Atmospheric rivers
Tropical forests act as moisture pumps, Walker tells UPI. “The forest recycles moisture, which supports regional rainfall. If you continue to destroy the forest, the rainfall amount drops … and eventually, you wreck the pump.”
He explains in his “Collision Course” paper that soybean farming in particular reduces evapotranspiration compared to native vegetation, leading to less rainfall. Conversion of the cerrado, to the east of the Amazon, to soybean plantations has reduced evapotranspiration and therefore reduced moisture transport into the Amazon Basin.
Moisture from the Amazon is transported in an “atmospheric river” into central South America. 23% of the rainfall in the La Plata River Basin comes from the Amazon.
Atmospheric rivers are crucial for agriculture and people living in southern Brazil, Paraguay, Uruguay, and northern Argentina. Atmospheric rivers recharge the Guarani Aquifer, and sustain the Pantanal wetlands.
Fire
Ranchers and farmers use fire is used to clear fields and pastures. The fires in 2019 highlighted the risks of the Amazon reaching a tipping point.
Undisturbed rainforests are humid and resistant to fire. But deforestation make rainforests vulnerable to fire. Logging roads make the problem worse. During droughts, agricultural fires can burn through nearby forest. Trees are killed and provide fuel for future fires. “In essence,” Walker writes, “fire produces fire in a positive feedback loop intensified by deforestation and drought.”
Infrastructure
Walker highlights the role of infrastructure development in the threat to the Amazon rainforest, in particular the Initiative for the Integration of the Regional Infrastructure of South America launched in 2000. The Initiative includes more than 300 projects, with a total budget of more than US$37 billion. The projects include large dams, industrial waterways, roads, ports, and energy and communications links. Walker points out the tipping points in the Amazon will likely be accelerated by infrastructure development.
Walker concludes by pointing out that it is not “just nature” that is threatened by an Amazon tipping point:
A tipping point transgression in Amazonia involves much more than the ecological consequences of forest destruction. To begin with, water security will falter for the 35 million who call the Basin home. This is hardly the full story, because moisture originating here provides much of the continent’s rainfall and river flow, which means that tens of millions of people in other parts of South America will grow thirsty and hungry if the Amazonian nations fail to stop a tipping point transgression, thereby allowing the south bound atmospheric rivers to run dry. The crowning irony is that the Initiative for the Integration of the Regional Infrastructure of South America regards the triborder region shared by Bolivia, Brazil, and Peru as critical to the continental plan. Unfortunately, forests in this southwestern corner of Amazonia are also critical to maintaining atmospheric moisture flow to the continent’s populous south. Thus, the development of Amazonia now lies on a collision course not only with the interests of conservation but also with the welfare of the very people it is meant to benefit.