[Updated Dec. 17, 2012, to reflect current research on fires in the Amazon and globally.]
For millennia, people have set fires to clear land for cultivation, pastures or hunting; so-called slash-and-burn agriculture is still common across much of tropical Africa, Asia and South America. It has been a useful strategy–but it is now becoming problematic. A new Earth Institute documentary shot in the Peruvian Amazon shows how.
Growing population, fragmentation of forests and warming climate are making the surface more prone to ever-larger escaped fires. These harm ecosystems and human infrastructure, cause health problems, and send up spirals of carbon and soot that may encourage even more warming of the atmosphere–and thus feed back into more fires. The documentary follows scientists investigating this global pattern on a personal scale: chasing down, and entering, fires set by farmers in Peru’s Ucayali River region. The aim of the multidisciplinary Fires in Western Amazon project is to figure out how fires get started; why some spread why others are contained; and what the future may hold. The project is funded by the U.S. National Science Foundation. (Click to Walk through a live blaze; to watch Peruvian farmers fighting a fire; or to see an interview with the project leader.)
Globally, as much as 5 million square kilometers–an area more than half the size of the United States–burns in a given year, according to a 2007 review by European, Canadian and African researchers. A 2012 study in the journal Environmental Health Perspectives estimates that wildfires, peat fires and controlled burns now kill 339,000 people each year, mainly by poisoning the air. The greatest number of deaths–some 157,000–are in sub-Saharan Africa. Southeast Asia ranks second, at 110,000.
Some fires come from natural causes such as lightning, but most are set by people, accidentally or on purpose. For small farmers, it is a convenient way to clear overgrown areas and release nutrients from standing vegetation back into the soil, says Miguel Pinedo-Vasquez, a native of the Peruvian Amazon,now an ecologist at the Earth Institute’s Center for Environmental Research and Conservation and co-leader of the fire project.
In many regions, rising temperatures and resulting declines in moisture may be helping drive more fires out of control. In addition, forests are being chopped into fragments, and the resulting lands more intensively occupied by humans. The results: a steady drumbeat of record fire seasons, including the catastrophic fires burning across much of the American West in summer 2012. New studies suggest these may be only the start for that region; one 2012 study projects that the area burned by U.S. wildfires, driven by warmer, drier conditions, will double by 2050. A 2010 study by the NASA Goddard Institute for Space Studies found that wildfires were common in previous centuries, but declined in the 20th century, with advances in firefighting technology. However, it predicts that they will soon resurge by as much as 35 percent, mainly due to temperature and precipitation shifts, as well as changing land use patterns. Another 2012 study, in the journal Ecosphere, predicts an increase especially in vast areas of the higher latitudes, but foresees decreases in the tropics. Some scientists think an increase is already underway: witness recent giant fires in Indonesia, Russia, Greece, Australia. A February 2012 study in the journal Geophysical Research Letters finds that the 2010 Russian heat wave that helped spark many fires was within the range of natural variability–but that human-induced climate change had tripled the chance of such a heat wave hitting. With fires sweeping the U.S. Southwest, officials such Tom Tidwell, director of the U.S. Forest Service, predict that it will probably get worse. Texas has had the hottest year on record, and changing climate has been blamed there for amplifying unprecedented drought and resulting wildfires that have destroyed thousands of homes and farms. Even large swaths of normally damp, fireproof northern tundra has been catching fire, as plants there dry out with hotter summers; this releases large amounts of carbon. A May 2011 report compiled for the United Nations says we may be headed for an age of “mega-fires” that will exceed all attempts at control.
A pair of 2011 studies in the journal Science suggest that fires, combined with changing climate and drier conditions in some places, could even be the trigger for quickly and permanently converting large swaths of earth’s forests into grasslands. Past conventional wisdom has been that such large-scale landscape changes take place only gradually with climate variations, and can shift back and forth. But the studies say that forests and grasslands are alternative long-term stable states, kept in place by strong relationships between vegetation and precipitation, and between seasonal rainfall and grasses. Once grasses are established, there is a very strong feedback loop between flammable grasses and fires that keeps trees from coming back.
Climate models disagree on whether the Amazon will dry out–but it did suffer the two biggest droughts of the past century in 2005 and 2010. A 2011 study in the journal Geophysical Research Letters led by the Earth Institute’s International Research Institute for Climate and Society showed how future droughts can be predicted months in advance by measuring seasonal temperature changes over the Atlantic Ocean–but that will not by itself prevent fires.
More immediately, the greater problem may be surging deforestation across the region. Particularly in the area around frontier city of Pucallpa, Peru, where the current study is taking place, migrants from the Andes are converting once-humid forests that previously contained only small, transitory farms into a checkerboard of permanent cultivation, abandoned fields and brushy second growth. This is a much more flammable arrangement, and puts the new infrastructure at risk. Many people from rural areas are now moving to newly booming Amazonian cities, and absentee landlords are using fires on massive scales to convert forests into pasture, and planting nonnative grasses that need fire to remain productive. The results are fires that escape and burn ever-growing areas, the exhaustion of soils, and the disappearance of native trees, plants and animals. Many of these problems are documented in a 2012 study by western Amazon fires study group, which appeared in the Proceedings of the National Academy of Sciences.
Development in Peru and neighboring Brazil is moving a further step: industrial-scale farms that grow oil palms, corn and other crops for international export, largely for conversion to biofuels. These big operations, which are replacing small farms, are managed not with fire, but with fertilizers, pesticides and machines; and once established, they are not as susceptible to fire as traditional farms. So, it is possible that escaped fires may eventually decline, whatever the climate does. On the other hand, the crops will in the end be burnt–not where they were raised, but in the gas tanks of faraway trucks, cars and other engines of modern living.