Climate Change and the Amazon Rainforest
Global climate change is happening now. The United Nations Framework Convention on Climate Change[PP1] (UNFCCC) defines climate change as a change in climate attributable directly or indirectly to human activity, and that occurs in addition to natural processes of climate variability observed over comparable periods of time. When released into the atmosphere through the burning of fossil fuels, deforestation, and other human practices, carbon dioxide and other greenhouse gases like methane absorb infrared radiation from the sun, trapping heat in Earth's atmosphere and altering the global atmosphere. Major and immediate impacts of climate change include increased flooding, storms, drought, and food insecurity, according to a recent World Bank report.
While skeptics argue that no evidence for "anthropogenic" or human-caused climate change exists, a report [S2] released by the Intergovernmental Panel on Climate Change in 2007 – the major conclusions of which have been validated by numerous follow-up studies – maintains that there is "unequivocal" evidence that global temperatures are indeed on the rise and that this phenomenon is "very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations."
The Amazon Basin and Climate Stability
Protecting the Amazon basin, which contains the largest tropical rainforest on the planet, is critical to our planet's climate stability. The rainforest serves as one of Earth's largest reservoirs of carbon dioxide, helping regulate global climate patterns through the sequestration and storage carbon dioxide in above-ground biomass and soil. By absorbing about 20 percent of the atmospheric carbon emitted by the burning of fossil fuels, the world's tropical rainforests can help mitigate climate change substantially.
As the source of one-fifth of all fresh water on the planet, the Amazon Basin's hydrological system plays a critical function in regulating the global and regional climate. Water condensation, evaporation, and transpiration over the Amazon are key drivers of the global atmospheric circulation, affecting precipitation across South America and much of the Northern Hemisphere. Among the regions directly linked to the Amazon by a complex weather system is the Rio de la Plata basin of southeastern South America, one of the most important agricultural zones on the planet. Recent climate models indicate that deforestation has also had the effect of reducing precipitation as far afield as the lower Midwest of the United States.
The Amazon's important contributions to global weather, however, are at risk as well. The Amazon serves as a carbon sink only so long as the rainforest absorbs more carbon dioxide than it releases which could soon change if patterns continue.
Worst-case Scenario: The Amazon Tipping Point
Human-induced climate change, if left unchecked, may soon cause the Amazon to emit more carbon into the atmosphere than it absorbs. Scientists predict this change could occur as Amazonian forests become less able to absorb atmospheric carbon as climate warming slows down plant growth in the region and causes trees to die more rapidly. Such was the case in 2005, when a prolonged drought in the Amazon released close to one billion tons of carbon dioxide into the atmosphere, more than it simultaneously removed through absorption.
As global temperatures rise, the Amazon could become caught in a potentially calamitous feedback loop. In this vicious cycle, warmer oceanic waters will continue to dry out the basin, which in turn will release more carbon into the atmosphere. Warmer temperatures and a dryer forest will also increase forest fires, emitting more carbon and driving the process.
In a February 2010 report[PP3] , the World Bank estimated that the "tipping point" for the Amazon could be approximately 20% deforestation. If reached, this threshold could trigger a dramatic die-back of the Amazon rainforest. With 17% to 18% of the Amazon already deforested, another similar amount degraded, forest fires running rampant, and global temperatures already on the rise, the Amazon ecosystem could face ecological collapse sooner than previously expected.
The World Bank report concludes: "There are four major, non-linear, positive-feedback responses to global warming with the potential to create major disruptions in global climate. These are the slowing of the North Atlantic Thermohaline Circulation, the breakup of the West Antarctic Ice Sheet, methane emissions from melting permafrost, and Amazon forest dieback. Of the four, only Amazon forest dieback can to some extent be mitigated by deliberate intervention at a global scale through the reduction in greenhouse gas emissions combined with efforts to avoid further deforestation."
This threat of a downward spiral calls for immediate and meaningful action to halt deforestation and climate change.