Cleaner air to worsen droughts
2008-05-08 12:45
Paris - Curbing a notorious form of industrial pollution may ironically harm Amazonia, one of the world's natural treasures and a key buffer against global warming, a study released on Wednesday has found.
Its authors see a strong link between a decrease in sulphur dioxide emissions from coal-fired power plants and a rise in sea temperature in the northern Atlantic that was blamed for wreaking a devastating drought in western Amazonia in 2005.
University of Exeter professor Peter Cox and colleagues created a computer model to simulate the impact of aerosols - airborne particles that, like sulphur dioxide, are also spewed out by fossil-fuel power plants - on Amazonia's climate.
The aerosols, while a bad pollutant, indirectly ease the problem of global warming as they reflect sunlight, making it bounce back into space rather than warm the Earth's surface.
In the 1970s and 1980s, according to Cox's model, high concentrations of aerosols over the highly industrialised northern hemisphere had the effect of buffering the impact of global warming on north Atlantic surface waters, which led to more rain over Amazonia.
But tighter curbs on sulphur dioxide emissions from power plants led to a reduction in aerosol levels, causing these Atlantic waters to warm. This changed patterns of precipitation, leading to the 2005 drought.
Projecting into the 21st century, the study estimates that by 2025 a drought on the same scale as in 2005 could happen every other year.
By 2060, forests would be starved for rainfall nine out of every 10 years, says the study, published in the British journal Nature.
What happens in Amazonia affects not just the region, but the entire world's climate system. Its rainforests contain a tenth of all the CO2 stored on Earth's land surfaces.
The loss of vegetation, through deforestation and drought, could have a dramatic impact on global warming, scientists have warned.
The study's findings point up the complicated interplay of factors involved in climate change.
"To improve air quality and safeguard public health, we must continue to reduce aerosol pollution, but our study suggests that these needs to be accompanied by urgent reductions in carbon dioxide emissions to minimise the risk of Amazon forest dieback," said Cox.
The UN's Intergovernmental Panel for Climate Change (IPCC) last year warned that rising global temperatures could transform much of South America's rain forests into semi-arid savannah-like areas within five decades.
Deforestation - caused by logging, agriculture and development - in the tropics accounts for up to 20% of global emissions of carbon dioxide, making it the second largest driver of global warming after the burning of fossil fuels.
Amazonia accounts for nearly half of those emissions.