Amazon Rainforest Tipping Point

A Vicious Circle

The hot, wet Amazon normally evaporates vast amounts of water, which rise high into the air as if in an invisible chimney. This draws in the wet north-East trade winds, which have picked up moisture from the Atlantic. This in turn controls the temperature of the ocean; as the trade winds pick up the moisture, the warm water that is left gets saltier and sinks. Deforestation disrupts the cycle by weakening the Amazonian evaporation which drives the whole process. One result is that the hot water in the Atlantic stays on the surface and fuels the hurricanes. Another is that less moisture arrives on the trade winds, intensifying drought in the forest. (reference)

Vast plumes of smoke from forest fires and agricultural burning are common in the tropics. Satellite evidence shows that these plumes reduce rainfall production and create huge rain-shadows over downwind areas. Rainforests return water to the atmosphere by transpiration from leaves. This is perhaps the most important regional ecosystem service, providing valuable moisture to downwind regions. Large-scale conversion of rainforest to pasture or cropland has the potential to undermine this service. (reference)

So far about a fifth of the Amazonian rainforest has been razed completely. Another 22 per cent has been harmed by logging, allowing the sun to penetrate to the forest floor drying it out. And if you add these two figures, the total is growing perilously close to 50 per cent, a threshold that current models predict as the tipping point that marks the death of the Amazon. These models did not predict this to occur before2050. However, the latest estimates indicate that the tipping point is indeed imminent.

The Amazon rainforest is the largest store of magnificent biodiversity on the planet, yet huge acreage continues to be destroyed by humans every year, both illegally and legally, due to agriculture, mining, cattle ranching, burning, and logging for timber. The Amazon River and its tributaries, teeming with life, and the beautiful creatures who live in the coastal and forest areas around these waters, are also threatened by proposed hydroelectric dams.

Incredibly, tropical rainforests are so fantastically rich with life, that although only 6% of the Earth’s surface is covered by rainforest, this 6% contains 50% of the world’s species. And, the Amazon rainforest which spans Brazil, Ecuador, Colombia, Suriname, Peru, French Guiana, Bolivia, Guyana and Venezuela remains the single largest area of rainforest in the world. In fact, the Amazon contains over half of the world’s total rainforest. (reference)

The picture on the right provides an aerial view of sediment run-off caused by massive deforestation. This entire area has been stripped bare of forest, so there are no longer any plants, bushes or tree roots to hold soil...which runs off into rivers and streams, killing marine life, even after the animals on land have been killed due to deforestation.

Aerial View of Sediment Run-off Caused by Massive Amazon Deforestation.

Until 2005, the only method used to monitor the progress of deforestation was the Amazon deforestation estimate project (PRODES, the Portuguese acronym), an annual analysis of around 200 high-resolution images taken of the Amazon region by the NASA Landsat satellite, supplemented by other satellite data when there are problems of cloud cover. By comparing vegetation cover within each image with those of the previous year, it is possible to get a pretty accurate estimate of the deforestation that has taken place in those 12 months. (reference)

The problem with this system was that by the time the complex analysis of each year's deforestation was complete, the damage has long since been done. It could therefore only be used as a historical record and of little use in aiding the authorities to chase after illegal deforesters. So in 2005 a new system was introduced as part of the Lula government's Amazon Deforestation Action Plan. The detection of deforestation in real time (DETER) system is designed to complement rather than replace PRODES. As the name suggests, the idea is to get data back quickly, using different satellites that generate much more frequent images, albeit at a lower resolution. Analysis from the DETER system is available every two weeks or so, and given the vastness of the Amazon region, the theory is that this should give the authorities valuable information about new areas of deforestation and guidance on where they should be concentrating their enforcement efforts.

The dynamics of deforestation in the Amazon are complex. he process tends to follow a distinct pattern: first a rainforest area is logged for its valuable lumber, then burned for cattle grazing, and as the land becomes exhausted, it is plowed up for crops such as soybeans. What is undoubtedly true is that the number of cattle in the Amazon has increased dramatically in recent years. The number of cattle in the Amazon region had reached 74 million in 2007, outnumbering people by more than three to one. Cattle numbers in the Amazon had grown 46 percent in just three years and the region had accounted for virtually the entire increase in the size of the Brazilian cattle herd between 2003 and 2006.

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Climate tipping points: Amazon Rainforest, Arctic Sea-Ice, Atlantic Thermohaline Circulation, Greenland Ice Sheet, Sahara/Sahel