http://www.guardian.co.uk/environment/2009/mar/11/amazon-global-warming-trees
‧ Scientists say 4C rise would kill 85% of the Amazon rainforest
‧ Even modest temperature rise would see 20-40% loss within 100 years
David Adam in Copenhagen
guardian.co.uk, Wednesday 11 March 2009 14.34 GMT
Article history
http://tinyurl.com/47u6bgu (jpg)
Data from Nasa's Terra and Aqua satellites are helping scientists to map the
rate at which plant life on Earth absorbs carbon out of the atmosphere
Global warming will wreck attempts to save the Amazon rainforest, according
to a devastating new study which predicts that one-third of its trees will be
killed by even modest temperature rises.
The research, by some of Britain's leading experts on climate change, shows
that even severe cuts in deforestation and carbon emissions will fail to save
the emblematic South American jungle, the destruction of which has become a
powerful symbol of human impact on the planet. Up to 85% of the forest could
be lost if spiralling greenhouse gas emissions are not brought under control,
the experts said. But even under the most optimistic climate change
scenarios, the destruction of large parts of the forest is "irreversible".
Link to this audio
Vicky Pope, of the Met Office's Hadley Centre, which carried out the study,
said: "The impacts of climate change on the Amazon are much worse than we
thought. As temperatures rise quickly over the coming century the damage to
the forest won't be obvious straight away, but we could be storing up trouble
for the future."
Tim Lenton, a climate expert at the University of East Anglia, called the
study, presented at a global warming conference in Copenhagen today , a
"bombshell". He said: "When I was young I thought chopping down the trees
would destroy the forest but now it seems that climate change will deliver
the killer blow."
The study, which has been submitted to the journal Nature Geoscience, used
computer models to investigate how the Amazon would respond to future
temperature rises.
It found that a 2C rise above pre-industrial levels, widely considered the
best case global warming scenario and the target for ambitious international
plans to curb emissions, would still see 20-40% of the Amazon die off within
100 years. A 3C rise would see 75% of the forest destroyed by drought over
the following century, while a 4C rise would kill 85%. "The forest as we know
it would effectively be gone," Pope said.
Experts had previously predicted that global warming could cause significant
"die-back" of the Amazon. The new research is the first to quantify the
long-term effect.
Chris Jones, who led the research, told the conference: "A temperature rise
of anything over 1C commits you to some future loss of Amazon forest. Even
the commonly quoted 2C target already commits us to 20-40% loss. On any kind
of pragmatic timescale, I think we should see loss of the Amazon forest as
irreversible."
Peter Cox, professor of climate system dynamics at the University of Exeter,
said the effects would be felt around the world. "Ecologically it would be a
catastrophe and it would be taking a huge chance with our own climate. The
tropics are drivers of the world's weather systems and killing the Amazon is
likely to change them forever. We don't know exactly what would happen but we
could expect more extreme weather." Massive Amazon loss would also amplify
global warming "significantly" he said.
"Destroying the Amazon would also turn what is a significant carbon sink into
a significant source."
Jones said the study showed that tree growth in high latitudes, such as
Siberia, would increase, but would be unlikely to compensate for the carbon
stocks lost from the Amazon. Even with drastic cuts in emissions in the next
decade, scientists say that there will only be around a 50% chance of keeping
global temperatures rises below 2C.
This best-case emissions scenario is based on emissions peaking in 2015 and
quickly changing from an increase of 2-3% per year to a decrease of 3% per
year. For every 10 years this action is delayed, the most likely temperature
rise increases by 0.5C.
Environmental campaigners said they were alarmed by the predictions. "With a
rise of over 2C you begin to see a large-scale change to savannah," said
Beatrix Richards, head of forest policy and trade at WWF UK. "You also lose
major ecosystem services, such as keeping carbon levels stable, providing
indigenous people with goods and services, and balancing rainfall patterns
globally from the US grain belt to as far away as Kazakhstan. A 4C [rise] is
a nightmare scenario that would move us into uncharted territory."
"People have known about the links between climate and forests for some time,
but the alarming thing now is the level of certainty because real world
observations are feeding into the computer models," said Tony Juniper, an
environmental campaigner and Green party candidate. "There really is no time
for delay. Governments must cooperate to cut industrial emissions while at
the same time halting deforestation, otherwise we'll have a mass extinction
and a global warming catastrophe."
A separate study from the Met Office shows that, if temperatures do reach 2C,
then there is a one-in-three chance they would stay that high for at least
100 years, whatever action was taken on carbon pollution.
The results were announced on the second day of a key climate science meeting
in Copenhagen, which is intended to spur politicians into taking action to
cut carbon pollution. It comes ahead of a UN summit in December, also in
Copenhagen, where officials will try to agree a new global deal on climate to
replace the Kyoto protocol. The results from the meeting will be published in
the summer as a supplement to the 2007 report of the Intergovernmental Panel
on Climate Change.
Positive feedback
Amazon dieback is one of the key positive feedbacks brought about by global
warming. These are typically runaway processes in which global temperature
rises lead to further releases of CO2 , which in turn brings about more
global warming. In the Amazon this happens on a more localised scale but the
result, increased forest death, also releases carbon into the atmosphere.
Experts predict that higher worldwide temperatures will reduce rainfall in
the Amazon region, which will cause widespread local drought. With less water
and tree growth, "homegrown" rainfall produced by the forest will reduce as
well, as it depends on water passed into the atmosphere above the forests by
the trees. The cycle continues, with even less rain causing more drought, and
so on.
With no water, the root systems collapse and the trees fall over. The parched
forest becomes tinderbox dry and more susceptible to fire, which can spread
to destroy the still-healthy patches of forest.
Other positive feedback effects expected by scientists, are releases of
carbon stored in frozen arctic ecosystems and an increase in the sun's energy
absorbed by the planet as ice melts.
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 114.44.21.39
※ 編輯: Dranoel 來自: 114.44.21.39 (02/05 14:16)