The Problem: Tropical Deforestation September 26, 2008
The Ecological Imperative
Tropical deforestation is one of humankind’s most urgent ecological security issues. Every acre of deforestation has multiple destabilizing consequences for climate stability. After fossil fuel combustion, deforestation is the largest source of CO2 emissions. The 5-6 gigatons (Gtons) of CO2 emissions from deforestation also cause massive collateral damage.
Tropical deforestation has four discrete negative impacts on Earth’s climate. These four impacts are discussed below individually, although the total impact may be more than simply cumulative.
Deforestation causes 15-20% of global greenhouse gas emissions. It is the 2nd largest source of CO2 emissions after fossil fuel combustion. Tropical deforestation emits an estimated 1.5 Gtons of carbon annually.
While variable across space and time, tropical forests probably absorb around 0.35 Gtons of carbon per year. By doing this CO2 removal, they have provided a strong negative feedback on atmospheric GHG accumulation. Most science suggests the uptake will last into the middle of this century. Cutting, clearing and burning tropical forests destroys theses terrestrial carbon sinks, accelerating the pace of climate change.
A third blow against climate stability is through biophysical feedbacks. The driving force of global atmospheric circulation is the export of heat and energy from the equator to the poles. Tropical forests are a large, albeit diminishing, green swath across the equator, where most incoming solar radiation strikes the Earth. Tropical forests can be thought of as a moist sponge that blankets our planet from the sun’s most intense radiation. For millennium, the biome has modulated the global radiation balance by altering the Earth’s surface albedo. In addition, tropical forests influence fluxes of sensible and latent heat to the atmosphere and the distribution of energy within the climate system. Tropical forests are vital to the stability of current climatic and weather patterns beyond the role they play in the global carbon cycle. By altering planet-wide land surface parameters, tropical deforestation has been shown to alter historical climate at the local, regional, and even global scale.
Natural forests perform a myriad of functions that will help offset some of global warming’s most punishing consequences. Locally, tropical forests help dampen extreme water events such as flooding. Tropical forests help prevent soil erosion. Natural mangrove forests regulate and cool water temperatures along coastlines. Native high-mountain forests provide refuge to species whose historic ranges have shifted or may shift due to global warming. The enormous stores of biodiversity in tropical forests may be valuable as we look for resources to combat diseases with expanded ranges and other symptoms of climate change. Thus, conserving tropical forests is not only a form of climate mitigation, but also is a crucial form of adaptation.
Tropical deforestation destroys more unique species than any other human activity. Tropical deforestation is the leading cause of species extinctions. Most estimates show that tropical deforestation has already resulted in 10,000 to 1,000,000 species extinctions. No other human process comes close to having eradicated so many of evolution’s byproducts. Ironically, if one reads today’s academic literature or popular articles, it would appear that climate change is the most severe threat to biological diversity. While the threat climate change poses to biodiversity is real and serious, it is decades away from being a major driver of species loss. By that time, if deforestation rates continue, much biodiversity will already have been driven extinct.
Tropical Deforestation Is a Dangerous Vector
Tropical forests harbor some of humanity’s nastiest plagues, including HIV, SARS, Ebola, and West Nile virus. Habitat loss, road building, and increased bush meat hunting associated with tropical deforestation have been implicated in lethal disease outbreaks. The US State Department concluded in 2003, that “Human exposure to the deadly Ebola virus is …more likely in areas where logging is underway”. HIV-1 jumped from a subspecies of chimp to man and probably spread along logging roads.
Deforestation causes flooding, leads to warmer waters and other impacts that spread disease. Outbreaks such as cholera, dysentery, hookworm and typhoid are known to thrive in conditions where forests have been cut. Deforestation may also cause the emergence of new diseases this world has yet to know. It is difficult to draw conclusive cause-and-effect pathways between deforestation and disease, but there is plenty of evidence to suggest the two go together. A detailed and readable examination of this topic is Laurie Garrett’s 1994 book, The Coming Plague.
Updated Resources on Tropical Deforestation (September 2008)
Intergovernmental Panel on Climate Change 4th Assessment
The Intergovernmental Panel on Climate Change (IPCC) is the authoritative voice on climate change science (for which they shared the 2008 Nobel Prize). The IPCC’s recent 4th Assessment Report is the latest in a series of synthesis reports. Click on the title above for the most pertinent parts on climate change and tropical forests. You can read the whole chapter, but the most important stuff starts on page 514, section 220.127.116.11.
Food and Agricultural Organization’s State of the World’s Forests
The FAO issues a report on global forest issues every two years. This report contains the latest aggregated data internationally. The 2007 report is kind of wishy-washy, we here at TFG find the 2005 report more useful.
Who Causes Deforestation? Less Rural Farmers, More Corporations
Authors Butler and Laurance show…”In an interval of just 1–2 decades, the nature of tropical forest destruction has changed. Rather than being dominated by rural farmers, tropical deforestation now is substantially driven by major industries and economic globalization.”