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.
"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)
