Amazon deforestation and global warming

The Amazon rainforest, sometimes called “the lungs of the world,” plays a key role in global climate, and it supports a diverse population of species, many of which exist nowhere else on Earth. Loss of Amazonian forest lands through both human clearing and drought has significant effects on climate regulation and Earth’s biodiversity.

Background

The Amazon rainforest occupies more than 2,300,000 square miles (5,957,00 square kilometers) of land in South America. About 60 percent is located in Brazil, with the rest spread across parts of Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname, and French Guiana. The rainforest has long been subject to deforestation from human activity, including loggers harvesting valuable tree species, farmers and ranchers expanding their agricultural operations, and mining companies seeking new resources. The pace of such activity began to increase sharply in the late twentieth century and remained strong in the early twenty-first century, generating growing concern from environmentalists.

Between 1970 and 2013, the total area of rainforest in Brazil shrank from 4,100,000 square kilometers to 3,341,908 square kilometers. The rate of annual rainforest clearing was at times slowed by international pressure and domestic conservation efforts, but continued to fluctuate over the years, often spiking as increased global demand for beef, soybeans, and ethanol encouraged the expansion of Brazilian agriculture. Changes in government policy also impacted deforestation rates. For instance, under the administration of Brazilian president Jair Bolsonaro (2019–23), deforestation of the Amazon in the country surged, whereas Bolsonaro's successor, President Luiz Inácio Lula da Silva, emphasized efforts to protect the rainforest.

A forest of this magnitude affects the world climate in numerous ways. On a regional level, dense vegetation supports higher temperatures, higher rainfall, less runoff, and lower daily and seasonal temperature fluctuations. In the long term, high global temperatures favor forests. On a geologic time scale, the warmest periods have coincided with the greatest extent of rainforest, whereas much of the area later occupied by the Amazon rainforest was savanna during the height of the last Pleistocene glaciation.

Plants extract carbon dioxide (CO₂) from the atmosphere via photosynthesis. An expanding forest acts as a carbon sink, removing CO₂ from the air and sequestering carbon in its woody parts. A mature forest is in equilibrium, emitting as much carbon through animal consumption and decomposition as it fixes through photosynthesis. Clearing or burning forests releases CO₂ into the atmosphere. If tree trunks are converted to lumber, and the land is subsequently used to grow crops, the net carbon release may be relatively small, but if the wood products are burned, and the land developed, the release can be considerable. Additionally, the clearing of forests destroys unique habitats and threatens biodiversity. The relationship between deforestation and climate change is complex, with both phenomena feeding into each other and intersecting with other environmental issues.

Contribution of Global Warming to Amazon Deforestation

Global climate change can affect a forest profoundly. Although warm temperatures, in general, favor rain forests, shifts in patterns of prevailing winds brought about by small changes in oceanic temperatures may bring drought to regions accustomed to high rainfall and flooding to formerly arid regions. Although such perturbations are common in the geologic record and the Earth’s biota has repeatedly shown a rapid response, the rate of recovery is slow on a human time scale. Additionally, the prospect of anthropogenic climate change—that caused by human activity—is considered differently than natural fluctuations in climate, long- or short-term.

Increasing atmospheric CO₂ may actually stimulate forest growth in the tropics. High carbon dioxide levels favor rapid growth of trees, which tend to crowd out understory species, leaving fewer niches for animal species, particularly insects dependent on specific food plants. In the short term, such highly productive forests may be commercially desirable for lumber production, but ecological diversity and sustainability suffer.

Cycles of the El Niño-Southern Oscillation (ENSO) cause large natural fluctuations in rainfall in the Amazon basin. During the unusually severe drought of 2005–6, some scientists predicted that tree species would die off and natural fires would destroy significant areas of forest, creating a climate feedback loop that would turn much of the Amazon into a savanna. The forest appears to be unexpectedly resilient, however. During a drought year, deep-rooted trees remain green, and they even grow faster than normal, owing to the absence of cloud cover. Still, longer-term drying trends are considered an ongoing threat to the Amazon and other rain forests.

Some efforts to address environmental problems elsewhere in the world have been noted to contribute to Amazon deforestation. Strenuous conservation efforts in the developed world, unaccompanied by a reduction in wood-product consumption, increase logging pressure in places like Brazil. The United States’ drive to produce and deploy corn-based ethanol opened the way for rapid growth in Brazil’s soybean production. Brazil is also a leading producer and exporter of ethanol derived from sugarcane. These crops are rarely planted directly on cleared jungle land, but cattle ranchers displaced by soybeans and sugarcane migrate to the Amazon, clearing forests for their herds.

Finally, decreasing levels of sulfur dioxide resulting from more stringent pollution controls in Europe and North America were implicated in Brazil’s devastating 2005 drought. This effect, the subject of a May 2008 article in Nature, was the first firm scientific evidence of the importance of sulfur dioxide emissions in canceling the greenhouse effect of carbon dioxide.

Contribution of Deforestation to Global Warming

The effects of Amazonian deforestation on world species diversity are more immediately visible and much more highly publicized than its large-scale climatic effects, as loss of the forest may lead to the extinction of thousands of species. Nonetheless, even if only carbon dioxide emissions are considered, the deforestation’s climatic effect is immense. Slash burning following logging may account for as much as half of Brazil’s carbon contribution to the atmosphere, estimated in the tens of millions of tons, though the nation has made efforts to reduce its emissions.

A 2015 study found Amazon deforestation was directly responsible for 1.5 percent of the total rise in carbon dioxide measured since the middle of the nineteenth century, though the related atmospheric carbon dioxide increase was low compared to sources such as fossil fuels. This and other studies made use of computer models to estimate changes in the forest over decades, as the most accurate satellite imagery allowing such measurements became available only around the turn of the twenty-first century.

Some of the released carbon is recaptured when land is used for crops or pastureland. However, indiscriminate logging combined with a drier and more uncertain climate due to global warming may ultimately convert large areas of the Amazon to semiarid grassland of minimal value as a carbon sink. This scenario, which appeared to many to be imminent during the 2005–6 drought, is now thought to be avoidable through feasible management schemes, some of which are already being implemented. However, economic and political factors pose challenges to such efforts.

Context

It is tempting to view environmental threats en masse and to assume that a policy that ameliorates one ecological disaster will have a correspondingly benign effect on others. The interactions between global warming and the deforestation of the Amazon rainforest demonstrate that this is not always the case. The forest has shown itself to be more resilient to drought than many scientists anticipated, though it remains highly threatened. The principal immediate, global-warming-related threat to the Amazon rainforest appears to be the rapid expansion of Brazilian agriculture in response to rising world demand for biofuels. Models for controlling this expansion so as to encourage efficient land use and sustainability favor large agricultural businesses over individual farmers and pay inadequate attention to preserving biodiversity, posing a new set of environmental problems.

No discussion of a global-warming issue is complete without mention of population issues. The populations of Brazil and other countries bordering on the Amazon grew at a rapid rate into the early twenty-first century. Despite the overall low level of energy consumption in the area, this population growth increases human impact on the environment exponentially. The Amazon ecosystem is apparently robust enough to withstand present levels of global carbon emissions, but unless exponential trends are reversed, the grim scenario of the degradation of rainforest to savanna looms in the future. The Brazilian National Space Research Institute, for example, warned that warming trends project to eventually turn as much as 30 to 60 percent of the Amazon rainforest into dry savanna.

Key Concepts

• carbon sink: an entity that absorbs and stores carbon, thereby removing CO₂ from the atmosphere
• rain forest: a tropical area dominated by evergreen trees whose leaves form a continuous canopy and that receives at least 254 centimeters of rain per year
• savanna: grassland with scattered trees, characteristic of tropical areas with seasonal rainfall on the order of 50 centimeters per year

Bibliography

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Cox, Peter M., et al. “Increasing Risk of Amazonian Drought Due to Decreasing Aerosol Pollution.” Nature, vol. 453, no. 1, 2008, pp. 212–215.

Gash, John H. C. Amazonian Deforestation and Climate. John Wiley, 1996.

Intergovernmental Panel on Climate Change. Climate Change, 2007—Impacts, Adaptation, and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by Martin Parry et al., Cambridge University Press, 2007.

London, Mark. The Last Forest: The Amazon in the Age of Globalization. Random House, 2007.

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Philips, Tom. "Amazon Deforestation Surges to 12-Year High under Bolsonaro." The Guardian, 30 Nov. 2020, www.theguardian.com/environment/2020/dec/01/amazon-deforestation-surges-to-12-year-high-under-bolsonaro. Accessed 12 Dec. 2024.

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Spring, Jake. "Exclusive: Brazil Launches First Anti-Deforestation Raids under Lula Bid to Protect Amazon." Reuters, 22 Jan. 2023, www.reuters.com/world/americas/first-brazil-logging-raids-under-lula-aim-curb-amazon-deforestation-2023-01-19/. Accessed 12 Dec. 2024.

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