Clean air could kill the Amazon, researchers say

Michael Kahn, Reuters 7 May 08;

LONDON (Reuters) - Cleaner air due to reduced coal burning could help destroy the Amazon this century, according to a finding published on Wednesday that highlights the complex challenges of global climate change.

The study in the journal Nature identified a link between reduced sulphur dioxide emissions from coal burning and increased sea surface temperatures in the tropical North Atlantic that boosts the drought risk in the Amazon rainforest.

With the rainforest already threatened by development, higher global temperatures could tip the balance, they said.

"Generally pollution is a bad thing but in this case improving the air may have ironically led to a drying of the Amazon," said Peter Cox, a researcher at the University of Exeter in Britain, who led the study.

"It shows you have to deal with greenhouse gases."

The Amazon -- the world's largest tropical rainforest -- plays a critical role in the global climate system because it contains about one tenth of the total carbon stored in land ecosystems.

The researchers used a climate-carbon model to simulate the impacts of future climate change on the Amazon and compared it to data from a 2005 drought that devastated a large chunk of the rainforest.

They estimated that by 2025 a drought on the same scale could happen every other year and by 2060 such a crisis could hit nine out of every ten years -- enough to turn the rainforest into savannah grassland, Cox said.

In the pre-industrial age, the Amazon was less vulnerable. But higher temperatures and destruction of the forest make droughts far more likely than in the past, the researchers said.

"The Amazon is said to be the lungs of the planet," Cox said in a telephone interview. "You don't want to damage it."

The researchers believe that efforts to clean up sulphate aerosol particles from coal burning at power stations in the 1970s and 1980s helps to explain the threat.

The pollution predominately in the northern hemisphere had limited warming in the tropical north Atlantic, keeping the Amazon wetter than it normally would have been.

But with that protection evaporating due to cleaner air and as greenhouse gases fuel global warming, the rainforest now faces a deadly drought risk, the researchers said.

"Reduced sulphur emissions in North America and Europe will see tropical rain bands move northwards as the north Atlantic warms, resulting in a sharp increase in the risk of Amazonian drought," Chris Huntingford, a researcher at Britain's Centre for Hydrology and Ecology said.

The findings highlight the need to deal not only with greenhouse gas emissions but also with the direct destruction of the rainforests as well, the researchers said.

They said 20 percent of global carbon dioxide emissions stem from burning of trees to build new homes and roads as development pushes farther into the delicate region, they added.

"You can argue there is a greater urgency to deal with the deforestation issue in our model," he said. (Reporting by Michael Kahn; Editing by Maggie Fox and Giles Elgood)

Cleaner air to worsen droughts in Amazon: study
Yahoo News 7 May 08;

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 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 percent 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.