Amazon more resilient to climate change
2013-02-06 21:22
Oslo - The Amazon rainforest is less vulnerable to die
off because of global warming than widely believed because the greenhouse gas CO²
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 CO² 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 are burnt.
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 CO²
in the atmosphere.
It estimated that the damaging effects of warming would
cause the release of 53 billion tons of carbon stored in lands throughout the
tropics, much of it in the Amazon, for every single degree Celsius of
temperature rise.
The benefits of CO² fertilisation exceeded those losses
in most scenarios, which ranged up to a 319 billion ton net gain of stored
carbon over the 21st century.
About 500 to 1 000 billion tons 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 said.
It did not factor in damaging effects from deforestation,
mostly burning to clear land for farms, which is blamed for perhaps 17% of
world greenhouse gas emissions from human activities.
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 UN negotiations on a
new treaty to slow climate change, due to be agreed by the end of 2015.
