Friday, May 20, 2011

Climate change and deforestation pose risk to Amazon rainforest

May 20, 2011

Deforestation and climate change will likely decimate much of the Amazon rainforest, says a new study by Brazil’s National Institute for Space Research (INPE) and the UK's Met Office Hadley Centre.

Climate change and widespread deforestation is expected to cause warmer and drier conditions overall, reducing the resistance of the rainforest ecosystem to natural and human-caused stressors while increasing the frequency of extreme rainfall events and droughts by the end of this century. While climate models show that higher temperatures resulting from global climate change will threaten the resilience of the Amazon, current deforestation is an immediate concern to the rainforest ecosystem and is likely driving regional changes in climate. Augmented by both global and locally-driven climate change, forest degradation is likely to have serious consequences for the region’s inhabitants, the Amazon’s vast diversity of species, and the global carbon budget.

The INPE-Hadley Centre’s Dangerous Climate Change in Brazil project emphasizes that regional climate change caused by deforestation in the Amazon will almost certainly be amplified by global climate change. But a reduction in deforestation in the Amazon would help mitigate climate change because forests act as sinks for atmospheric carbon, which is stored in forests as vegetation grows, but released into the atmosphere when they are cleared or burned. Reducing deforestation would also boost the resiliency of the Amazon rainforest to stresses related to tree mortality such as wind, fire, and increased temperature from regional warming under climate change.

However, if widespread deforestation continues, the news is bleak. According to the study, if forty percent of the Amazon were to be deforested, the rainforest ecosystem would pass a 'tipping point' that would trigger a feedback loop between forest loss and climate impacts. Warming of three to four degrees Celsius in the Amazon region would likely engage a similar tipping point. Such a point may not be far off.

Climate models predict possible warming in the Amazon between two and nine degrees Celsius by the end of the century. Any warming is expected to decrease rainfall in the Amazon, particularly in eastern Amazonia. Climate model projections for 2080 suggest that if global temperature were to rise 1.8 degrees Celsius, rainfall in the Amazon would decrease by eleven percent. Should world temperature rise to 4.8 degrees Celsius, Amazonian rainfall would decrease 32 percent. Rainfall in the Amazon could decrease 41 percent if global temperature were to rise just over six degrees Celsius.

The sensitive hydraulic cycle of the Amazon could also be at risk if even 30 percent of the forest is cleared. The rainforest recycles up to half of its rainwater, and a positive feedback loop of forest loss and decreased rainfall would threaten the stability of Amazonian ecosystems. Additional warming from climate change would accelerate the process of ecosystem alteration and its warming, drying effects.

Stressors on the Amazon rainforest could impact the whole continent. The Amazon plays a crucial role in regulating the climate of South America through its influence on the regional water cycle; therefore, large-scale deforestation in the rainforest compounded by global climate change could decrease the forest's ability to recycle rainfall and transport moisture to other parts of the continent.

By reducing the Amazon's capacity to absorb carbon, modifying regional water cycles, and increasing soil temperatures, deforestation and climate change could cause the Amazon to die back and be replaced with savannah-like vegetation. Such ecosystem alterations could drive major economic distress in Brazil: more than 70 percent of Brazil’s energy is produced by hydropower, and reduced rainfall related to forest death would limit the electricity supply to industrial areas. Meanwhile, dry conditions would exacerbate wild fires, which would in turn send more carbon into the atmosphere.

Even more worrisome than changes in average temperature and rainfall is the increased likelihood and frequency of extreme weather events related to climate change and regional deforestation. The Amazon has experienced two droughts and record flooding within the last five years. The 2005 and 2010 droughts fit the analysis of some climate models that projected significant drying and warming of the Amazon by the end of the century. The INPE-Hadley Centre study estimates that drought years like 2005 are now a one in twenty year event, but they could be a one in two year event by 2025 and a nine in ten year event by 2060 given current trends of climate alteration. Droughts and floods are part of the natural climate variability of the Amazon, but the risk of severe weather is expected to increase with worsening climate change. The 2005 drought greatly reduced fish yields and had a negative impact on the transportation, agriculture, and hydropower sectors, while a 2009 flood displaced thousands and led to serious public health issues related to water-borne disease.

The Brazilian government has pledged to curb deforestation in the Amazon eighty percent by 2020. Deforestation in the region did fall from 27,000 km2 in 2004 to 6,500 km2 in 2010, but the Brazilian government reported this week that deforestation has increased almost sixfold in the last year. The INPE-Hadley Centre study estimates that if large-scale weather patterns continue to be altered by climate change while deforestation increases the frequency of Amazonian drought, 55 percent of the Amazon will be lost over the next twenty years.

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