POSTED 6 APRIL 2006
Bye-bye amazing Amazonia?
Among Earth's "vital organs," the tropical rainforests have always played a special role. Home to unparalleled human and biological diversity and the source of mammoth rivers, rainforests have been an international cause for decades. Nowhere has the concern about rainforest deforestation been greater than in the Amazon basin of South America, site of the largest rainforest of them all.
Farmers, miners, and ranchers have flooded to the basin, and every year, fires consume more territory. In 2005, 17 percent (650,000 square kilometers) of the Brazilian Amazon was deforested, says Carlos Souza, a Brazilian remote-sensing expert.
Now, a new set of maps of roads, fires, agriculture, cities, and other disturbances to the Brazilian rainforest, show that the human impact now affects about 50 percent of the forest -- far more than the amount deforested. "This was the first comprehensive set of indicators compiled and looked at together," says Ruth Nogeuron, who worked with Souza on a new mapping project for Imazon and the World Resources Institute (WRI).
Plenty of mapping projects have looked at fires, the expansion of agriculture, and deforestation, but the recent project aimed to identify not deforestation so much as the preconditions for deforestation, Souza told us. "Once you already have deforestation, it's too late. With these indicators showing where the pressure is, and what are the reasons for it, we can prioritize the creation of new protected areas."
The maps could slow deforestation by showing where and how it's happening, Souza told The Why Files. "Local people don't perceive the problem, because they don't have a good sense of where the development is, where the frontier is. When they see the maps, they become supportive of the government policy" to establish conservation areas. The government has placed 40 percent of the Amazon under some form of protection, although some of this protection seems better on paper than it is in reality.
A study published last week in Nature predicted that 40 percent of the Amazon will be deforested by 2050, if present trends continue (see "Modeling Conservation..." in the bibliography). Beyond the destruction of biodiversity, scientists are starting to explore how such massive deforestation could change the climate.
Rainforest trees recycle water back to the atmosphere, where it generally forms clouds and more rain, so cutting trees could reduce rainfall and cause more water to reach the ocean through rivers. That seems to be happening. "We have seen a 30 percent increase in the flooded part of the Amazon due to vegetation removal," said Jonathan Foley of the University of Wisconsin-Madison.
Original photos: NASA's Goddard Space Flight Center
Deforestation may also reduce rainfall by depriving clouds of nuclei where water droplets can form. Vegetation makes volatile organic compounds called terpenes that form these nuclei, Kevin Noone of Stockholm University told AAAS, so "There is a feedback loop between vegetation and a condition necessary for the vegetation."
The downstream effects of deforestation could extend far beyond South America, said Noone, the executive director of the International Geosphere Biosphere Program. IGBP is an interdisciplinary project to understand global change in terms of atmosphere, ocean and land -- no trivial task IOHO (in our humble opinion).
Computer climate models show major rainfall reductions in the Western Hemisphere, and possibly further away, Noone said. "Teleconnection is something we need to analyze and understand in describing how we perturb the Earth system."
And deforestation could directly accelerate global warming, noted Carlos Nobre, director of the Brazilian Centre for Weather Forecasting and Climate Studies. "A complete forest die-back would, as a start, pump about 100 billion tons of carbon into the atmosphere, increasing global warming," Nobre wrote us. (Current human activities pump about 6.1 billion tons of carbon into the atmosphere each year.)
Photo: World Resources Institute
Brazilian scientists are also concerned about the type of tipping point we have already mentioned. Northeast Brazil is a large hunk of land bordering the Amazon where conditions are already dry, but could be moving drier, Nobre said.
The current status of climate and environment in Amazonia is not the only possible one, Nobre says. In the dry season, deep-rooted trees retain water and nutrients, which is why forest can survive in seasonally dry areas. But increased fires, accelerated by global warming, could result in a "second equilibrium state," he warns. Global warming is expected to warm Amazonia by 3 degrees to 5 degrees C by 2070 to 2100, which could kill off 43 percent of 69 tree species by the end of the century. "This indicates severe vulnerability of the Amazon ecosystem to biosphere change. It could shift to a second equilibrium state, with much less forest and much more savanna," Nobre said.
A similar change occurred in the Sahara 6000 years ago, he added. "It appears that vegetation-atmosphere interactions played a central role for the rapid change from a more vegetated state to the current barren land," over hundreds of years.
While we're talking Brazil, a highly unusual hurricane brewed up in the South Atlantic in March, 2004. A recent study (see "The First South Atlantic Hurricane..." in the bibliography) blamed global warming for this unsettling storm.
Vegetation and land use affect the atmosphere in Amazonia. How else do our vast farms change the Earth?
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive