* Greenhouse gas CO2 will act as a fertiliser-Nature study
* Boost to Amazon growth exceeds damage from temperatures
By Environment Correspondent Alister Doyle
OSLO, Feb 6 The Amazon rainforest is less
vulnerable to die off because of global warming than widely
believed because the greenhouse gas carbon dioxide also acts as
an airborne fertiliser, a study showed on Wednesday.
The boost to growth from CO2, the main gas from burning
fossil fuels blamed for causing climate change, was likely to
exceed damaging effects of rising temperatures this century such
as drought, it said.
"I am no longer so worried about a catastrophic die-back due
to CO2-induced climate change," Professor Peter Cox of the
University of Exeter in England told Reuters of the study he led
in the journal Nature. "In that sense it's good news."
Cox was also the main author of a much-quoted study in 2000
that projected that the Amazon rainforest might dry out from
about 2050 and die off because of warming. Others have since
suggested fires could transform much the forest into savannah.
Plants soak up carbon dioxide from the atmosphere and use it
as an ingredient to grow leaves, branches and roots. Stored
carbon gets released back to the atmosphere when plants rot or
A retreat of the Amazon forests, releasing vast stores of
carbon, could in turn aggravate global warming that is projected
to cause more floods, more powerful storms and raise world sea
levels by melting ice sheets.
"CO2 fertilisation will beat the negative effect of climate
change so that forests will continue to accumulate carbon
throughout the 21st century," Cox said of the findings with
other British-based researchers.
ROOT AND BRANCH
The scientists said the study was a step forward because it
used models comparing forest growth with variations in the
rising levels of carbon dioxide in the atmosphere.
It estimated that the damaging effects of warming would
cause the release of 53 billion tonnes of carbon stored in lands
throughout the tropics, much of it in the Amazon, for every
single degree Celsius (1.8F) of temperature rise.
The benefits of CO2 fertilisation exceeded those losses in
most scenarios, which ranged up to a 319 billion tonne net gain
of stored carbon over the 21st century. About 500 to 1,000
billion tonnes of carbon are stored in land in the tropics.
Climate change would be more damaging for the Amazon if
greenhouse gases other than CO2, such as ozone or methane which
do not have a fertilising effect, take a bigger role, the study
It did not factor in damaging effects from deforestation,
mostly burning to clear land for farms, that is blamed for
perhaps 17 percent of world greenhouse gas emissions from human
Brazil has sharply reduced forest losses in recent years.
But predictions of a die-back in coming decades had led some
people to conclude that there was no point safeguarding trees.
"Some people argued bizarrely that it would be better to
chop them down and use them now," Cox said, adding that the new
findings meant that reasoning was no longer valid.
By underlining the importance of trees for soaking up CO2,
the study could also bolster slow-paced efforts to create a
market mechanism to reward nations for preserving tropical
forests as part of U.N. negotiations on a new treaty to slow
climate change, due to be agreed by the end of 2015.
(Editing by Robin Pomeroy)