The United Nations' climate change panel is facing fresh criticism after new research contradicted the organisation's claims about the devastating effect climate change could have on the Amazon rainforest.
A new study, funded by Nasa, has found that the most serious drought in the Amazon for more than a century had little impact on the rainforest's vegetation.
The findings appear to disprove claims by the Intergovernmental Panel on Climate Change (IPCC) that up to 40% of the Amazon rainforest could react drastically to even a small reduction in rainfall and could see the trees replaced by tropical grassland.
The IPCC has already faced intense criticism for using a report by environmental lobby group WWF as the basis for its claim, which in turn had failed to cite the original source of the research.
Scientists have now spoken out against the 40% figure contained in the IPCC report and say that recent research is suggesting that the rainforest may be more resilient to climate change than had been previously thought.
It comes just days after the UN announced an independent review into the panel's procedures following a series of scandals over its most recent report which was found to contain factual errors and claims which were not based on rigorous scientific research.
The InterAcademy Council, which is the umbrella organisation for the national academies of science around the world, will examine how the IPCC's reports are compiled and communicated.
Dr Jose Marengo, a climate scientist with the Brazilian National Institute for Space Research and a member of the IPCC, said the latest study on the Amazon's response to drought highlighted the variations on the previous claims.
He said: "In 2005, some parts of the Amazon were affected by the drought and others were not. In some regions, dryness was high and the number of fires was high. In other areas, the forest was not affected.
"As part of its standard processes, the IPCC assesses new papers in each assessment cycle. New literature that has appeared since the 2007 report will be reviewed for the next report."
The new study, conducted by researchers at Boston University and published in the scientific journal Geophysical Research Letters, used satellite data of the Amazon rainforest to study the effects of a major drought in 2005 when rainfall fell to the lowest level in living memory.
The drought saw rivers and lakes dry up, causing towns and cities that rely upon water flowing out of the rainforest to suffer severe water shortages.
But the researchers found no major changes in the levels of vegetation and greenery in the forests despite the drought.
They claim this contradicts the statements made in the IPCC's 2007 assessment report on climate change.
It said: "Up to 40 % of the Amazonian forests could react drastically to even a slight reduction in precipitation; this means that the tropical vegetation, hydrology and climate system in South America could change very rapidly to another steady state.
"It is more probably that forests will be replaced by ecosystems that have more resistance to multiple stresses caused by temperature increase, droughts and fires, such as tropical savannahs."
Professor Ranga Myneni, from the climate and vegitation research group at Boston University who was the senior researcher in the new study, criticised the IPCC’s claim that a “even a slight reduction in precipitation” would cause drastic changes in the rainforest.
He said: “There was more than a slight reduction in precipitation during the drought of 2005. It is that particular claim of the IPCC that our analysis rejects.”
Sangram Ganguly, a scientist from the Bay Area Environmental Research Institute in California and one of the researchers who conducted the new study, said: "Our results certainly do not indicate such extreme sensitivity to reductions in rainfall."
Dr Arindam Samanta, the lead author of the study, said: "We found no big differences in the greenness levels of these forests between drought and non-drought years, which suggests that these forests may be more tolerant of droughts than we previously thought."
The IPCC has been left embarrassed after it emerged the panel had quoted unsubstantiated and erroneous claims about the melting of glaciers in the Himalayas and had also used information from student dissertations and magazine articles to compile its report.
The chair of the panel, Rajendra Pachauri has come under mounting pressure to resign following the scandal and questions over his ability to lead the organisation.
Dr Keith Allott, head of climate change at WWF UK, said: "The WWF report from 2000 on the threat of wildfires in Amazon was based on respected sources and peer-reviewed literature available at the time.
"Subsequent peer-reviewed literature has confirmed that the Amazon faces serious risks from climate change. This new study is a welcome addition to the growing body of evidence."
Dr Simon Lewis, an expert on forest die back at Leeds University and a research fellow at the Royal Society, said the Boston University study had helped to clear up debate about how the rainforest responded to short-term drought.
But he added that long-term reductions in rainfall might have a very different impact.
No one was available to respond at the IPCC yesterday.