Clean air could kill the Amazon, researchers say

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By Michael Kahn

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.

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"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)