• 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, guardian.co.uk 11 Mar 09;
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".
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.
Climate change transforming rainforests into major carbon emitters, warn scientists
Although carbon dioxide encourages growth trees die younger, claims researcher
Oliver Tickell, guardian.co.uk 11 Mar 09
Drought, rising temperatures and deforestation are causing tropical forests to change from carbon sinks into a major carbon emitter, warn scientists from the UK and Australia.
Climate modellers had assumed, the scientists said, that rising levels of CO2 in the atmosphere would increase the growth of trees because CO2 can encourage plants to grow, and in turn absorb more of the greenhouse gas. However, the models are said to have left out one key factor: trees also die younger as their metabolic rate is increased.
"Most carbon is in living trees, and tree mortality is not included in the models," said David Hilbert of research organisation CSIRO at the Climate Congress in Copenhagen. "Trees grow faster with higher temperatures, but mortality goes up too. So despite higher tree growth and higher turnover of biomass, rainforests in a warmer climate have a reduced carbon storage capacity."
The results are based on detailed observations of 117 rainforests sites around the world, with the effect most marked in Africa. The implications could be highly significant, said Hilbert. Every degree centigrade of temperature increase, he has calculated, will result in 14 tonnes of carbon emissions per hectare of rainforest, equating to 24.5 gigatonnes (Gt) of carbon worldwide – two and a half times the world carbon emissions in 2007.
At a warming rate of 0.05C per year, forests will produce 1.2Gt a year of carbon, more than they are currently absorbing as a sink (about 1Gt a year).
Simon Lewis of Leeds University said the warning is based on a study of emissions from the Amazon during the drought year of 2007, which showed that the world's biggest tropical forest emitted a colossal 1.4Gt of carbon over the year, about 1% of its embodied carbon content. "The Amazon was transformed from a carbon sink into a major carbon source," he said. "This was partly a result of depressed growth, but more importantly of a mortality increase. The forest may bounce back if this drought was a one-off event, but the worry is if these droughts occur more frequently or are more severe."
He added that the threat of forest fires also needs to be taken into account: "People will burn tropical forests if they can get them alight to clear land for agriculture, and in remote areas these fires can go badly out of control. Under warmer, drier conditions the fires will light more easily and burn more forest over a longer period of time." The Australian forest fires last month, which claimed more than 180 lives, were estimated to have released millions of tonnes of carbon dioxide into the atmosphere.
According to Lewis, tropical forests have served as a "free" carbon sink without our knowledge, soaking up about 1Gt of carbon a year to offset human emissions, thanks in part to the carbon fertilisation effect. "We cannot, however, count on this sink working forever," he said. Hilbert's observations of rising tree mortality under higher temperatures, combined with Lewis's measurements of rapid carbon emissions from the Amazon under drought conditions, show that
this important free sink will quickly turn into a carbon source once significant climate change takes effect.
The key policy at this stage, added Lewis, must be to protect forests from industrial logging and deforestation.
Amazon rainforest at risk of ecological 'catastrophe'
Climate change could kill the Amazon rainforest even if deforestation and emissions are curbed, scientists at the Met Office fear.
Richard Alleyne, The Telegraph 12 Ma r09;
Even small rises in temperature could destroy large swathes of the jungle, they believe.
Changing rainfall patterns already under way could leave up to three quarters of the forest dry and withered by the middle of the next century.
The result would not only be an ecological "catastrophe" but could also turn the global weather system on its head, the researchers said.
The findings were presented to the climate summit in Copenhagen by scientists at the Met Office’s Hadley Centre in Exeter, which specialises in climate prediction and research.
The team has calculated that if, as widely anticipated, the world’s average temperature rises by 2 degrees Celsius (3.6 degrees Fahrenheit) from the pre-industrial levels of around 14C (57F) by the middle of the century, then between 20 and 40 per cent of the Amazon’s trees will disappear.
If the more pessimistic predictions of a 3 degree C rise are correct, then as much as 75 per cent of the forest will be destroyed by 2150.
The process, once started, could take hundreds of years to reverse.
Even the most modest predictions of a 1 degree C rise will see some irreversible damage to the tree coverage.
Dr Chris Jones, co-author of the study, said: "On any level of pragmatic timescale we should see any loss of the Amazon forest as irreversible.
"It is hard to quantify its effect on world climate but it would not be insignificant."
The team believes that the process, known as dieback, will begin when average global temperatures reach around 15C. Weather system changes will mean less rainfall on the jungle which will result in saplings failing to reach maturity while older trees die and wither away.
Once the process begins it will feed on itself as less tree cover will mean less water evaporation to create more rain. Eventually it could have the effect of turning more than a million square miles of the jungle in Brazil into savannah.
The process would be accelerated by logging, which often involves burning down the wood, releasing carbon, to clear it for agriculture.
However, a reduction in logging would help the rainforest to survive changes in climate.
Prof Peter Cox, Met Office professor of climate system dynamics at the University of Exeter, said: "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.
"It would amplify global warming significantly. Just as an example: at the moment deforestation adds about a fifth of the world’s carbon to the atmosphere."
Prof Tim Lenton, professor of earth systems science at the University of East Anglia, called the findings a "bombshell".
He said: "When I was young I thought chopping down the Amazon would destroy the forest, but now it seems that climate change will deliver the killer blow."
Dr Vicky Pope, of the Hadley Centre, said: "This research shows that the impact will be much greater than previously thought. We are storing up enormous trouble.
"The damage won’t be immediately apparent but we could be storing up huge problems for the future. There is a time lag.
"If these higher temperatures are sustained over 100 years or more the effects could be devastating."
Fate of the rainforest is 'irreversible'
A third of the Amazonian 'carbon sink' is doomed whether or not emissions are cut, Copenhagen conference is told
Michael McCarthy, The Independent 12 Mar 09;
The impact of climate change on the Amazon rainforest could be much worse than previously predicted, new research suggests.
Even if emissions were reduced and governments managed to limit temperature rises to 2C – the current aim of international climate policy – between 20 and 40 per cent of the forest could die because of warming, a British scientist told a conference on climate change in Copenhagen yesterday.
Dr Chris Jones, of the Met Office's Hadley Centre for Climate Prediction and Research, said the Amazon may become "committed" to substantial change by rising temperatures long before any such change is apparent elsewhere.
The effect would be caused by the inertia of the Amazon's ecosystem – a phenomenon by which changes take a long time to work through the system to their fullest. This is already known to occur in the oceans, which is why sea level rise is expected to continue for centuries after any stabilisation of global warming.
The discovery that ecosystems can also be committed to large-scale changes means the danger to the natural world from the warming atmosphere may have been underestimated.
A 40 per cent loss of the Amazon rainforest, as well as being a disaster for wildlife and the people of the region, would make climate change worse because it would damage the region's ability to act as a carbon "sink", soaking up the main greenhouse gas, carbon dioxide.
The loss would be in addition to the losses presently caused by deforestation.
Dr Jones said: "Ecosystems do exhibit significant commitment to further change even after you've stabilised the climate. The Amazon forest will be committed to large-scale loss long before any is observable in the real world, so some kind of monitoring system to detect the first signs of Amazon dieback might actually be too late. We need to understand the processes responsible before that."
The computer model used to forecast forest losses showed that commitment to change came in at a temperature rise of about 1 C above the level existing before the industrial revolution in the 18th century.
Currently, global temperatures are about 0.75C above the pre-industrial level. However, scientists believe that large amounts of carbon dioxide emitted in recent years have caused further warming of about 0.6C – meaning that the world is likely to warm at least 1.3C, even if all carbon emissions were stopped immediately.
Asked if this meant Amazon dieback had already started, Dr Jones responded that it probably had. At 1.3C, the commitment to change is not great, but by C it rapidly leaps up to 20 and then 40 per cent loss of forest. At 3C – where the computer simulation shows no dieback might yet be visible – the commitment is a 70 per cent loss of the forest.
Dr Jones said these changes could be reversible only over very long time scales – perhaps hundreds of years. "On any kind of pragmatic time scale, I think we should see loss of the Amazon forest as irreversible," he added.
Despite the long-term term threat of Amazon forest dieback, Vicky Pope, the Hadley Centre's head of climate advice, said it was still important to try to continue to stop deforestation because it was leading to as much emissions being pumped into the atmosphere as the world's transport sector.
