James Painter, BBC News 16 Feb 09;
A study by a group of UK-based scientists suggests that the Amazon rainforest may be less vulnerable to severe drying as a result of global warming than previously thought.
However, the scientists warn that the rapid degradation of the rainforest known as "dieback" caused by human-induced climate change remains a "distinct possibility" this century.
For the first time, the scientists compared the simulations of 19 global climate models with real-life climate observations. Their work is published in the Proceedings of the National Academy of Sciences (PNAS) journal.
Their main conclusions are that:
• almost all the climate models underestimated the current amount of Amazonian rainfall, because they are unable to capture the peculiarity of the geography of South America.
• sections of rainforest in the eastern part of the Amazon, which is currently wet all year round, are likely to become "seasonal forests" which have a wet and a dry season.
• but there will probably still be enough rainfall during the year not to turn it into savannah (dry, flat grassland).
• the Western part of Amazonia is likely to keep a climate and pattern of rainfall conductive to maintaining a rainforest, although the drier margins in the north and south may not.
Other projections, including those of the UN Intergovernmental Panel on Climate Change, have suggested that the eastern part of the Amazon could gradually be replaced by savannah.
This new study warns that even though these seasonal forests may be more resilient to occasional drought, they will be more vulnerable to fires.
Parts of the eastern region of rainforest will become tinderboxes, the study says, if deforestation, logging and the widespread use of fire is not controlled.
Last year, the dieback of the Amazonian rainforest was described by a group of international scientists as one of the nine potential "tipping points" in the Earth's climate system that lead to changes that can be sudden and dramatic rather than gradual.
This new study warns that the best way of minimising the risk of Amazon dieback was to control global greenhouse gas emissions. But it adds that government action is also needed.
"Forest protection within this area could play a major role in minimising the prospects of major dieback, whilst also contributing to tackling global climate change," said lead author Professor Yadvinder Malhi from the Environmental Change Institute at the University of Oxford.
"Forest cover can help to maintain local rainfall in the dry season, limit the spread of fires and stop surface temperatures rising too high."
Conserving tropical rainforests is seen by many as a promising way of reducing greenhouse gas emissions. Deforestation is estimated to be responsible for nearly 20% of such emissions every year.
Last August the Brazilian government launched an international fund to protect the rainforest and help to combat climate change, which intends to raise more than US$20bn (£14bn) by 2021.
The government also aims to reduce deforestation by 70% over the next 10 years.
"Even with sufficient funds and will power, the implementation of biosphere management on such a scale will be a substantial challenge," say the authors of the new study.
"Understanding the social, political and economic context will be critically important."
