Scientists: new study does not disprove climate change threat to Amazon

Jeremy Hance
March 19, 2010

Scientists' write that press release based on study was "misleading and inaccurate".

Recently, Boston University issued a press release on a scientific study regarding the Amazon's resilience to drought. The press release claimed that the study had debunked the Intergovernmental Panel on Climate Change's (IPCC) theory that climate change could turn approximately 40 percent of the Amazon into savanna due to declining rainfall. The story was picked up both by mass media, environmental news sites (including mongabay.com), and climate deniers' blogs. However, nineteen of the world's top Amazonian experts have issued a written response stating that the press release from Boston University was "misleading and inaccurate".

The study in question, published in Geophysical Research Letters, showed that the forests' level of 'greenness' had not changed during the 2005 year drought (see mongabay.com's original coverage of the study and press release: Amazon confusion: new research shows forest is resilient to drought, but is this the whole picture?). However it was not the study, but the press release, entitled 'New study debunks myths about Amazon rain forests', that has disturbed some of the world's most notable Amazon experts.

Forest clearing in the Amazon: Mato Grosso, Brazil. Photo by Rhett A. Butler.
"[The press release] claims that the study 'debunks myths about Amazon rainforests', which is simply not true," the experts' letter reads. "First, there is no myth. Rather, there are multiple, consistent lines of evidence from ground—based studies published in the peer—reviewed literature that Amazon forests are, indeed, very susceptible to drought stress. Second, nothing is debunked by the new study. The new study contributes to our understanding of interpretations of data retrieved from satellites, but it does not prove or disprove anything about what is really happening on the ground."

The researchers add that while the BU press release was inaccurate, the study it reports on has added "to our knowledge of Amazon forests". While a previous study had shown that the Amazon may have actually benefited from the 2005 drought, i.e. the forest was 'greener' than usual, the new study found no change in the forests 'greenness'.

However, the impact of drought should not only be measured by forest 'greenness'. To prove this the letters' experts cite a recent study that found a "large surge" in tree mortality in 2005 that was consistent with the results of two experiments showing tree mortality after rain reductions.

"These studies, published in some of the best peer—reviewed science journals, provide several consistent lines of evidence that the forests of the Amazon Basin are susceptible to small reductions in rainfall," the experts conclude, adding that drought also increases the susceptibility of the Amazonian rainforest to fire, citing fires in 2005 and in 1998 during another drought. Unlike temperate forests, fire is a rare occurrence in rainforests unless started by humans or, in this case, caused by rare droughts.

The scientists also used the letter to defend the findings of the 2007 IPCC report, which stated that 40 percent of the Amazon could become savanna due to climate change-exacerbated drought conditions.

"While the IPCC statement could be criticized for citing a review paper rather than original research papers, the main conclusion of the IPCC statement—that Amazonian forests are very susceptible to reductions in rainfall—remains our best understanding of the data available at the time of the IPCC report and also today," the letter reads.

Furthermore, the researchers note that while the IPCC report cites gray literature—a WWF report—rather than a research paper, the WWF report did not just pull its information out of thin air, but from research published in the peer-reviewed journal Nature.

The scientists say that the fact that climate change could 'flip' large portions of the Amazon, approximately 40 percent, into savannah, was not only accurately reflecting the research of the time, but "has been reinforced by new studies."

The letter is signed by: Daniel Nepstad, Woods Hole Research Center, USA, and Instituto de Pesquisa Ambiental da Amazonia, Brazil; Ane Alencar, Instituto de Pesquisa Ambiental da Amazonia, Brazil, and University of Florida, USA; Greg Asner, Carnegie Institute of Science, USA; Alessandro Baccini, Woods Hole Research Center, USA; Paulo Brando, Instituto de Pesquisa Ambiental da Amazonia, Brazil, & University of Florida, USA; Foster Brown, Woods Hole Research Center, USA & Universidade Federal do Acre, Brazil; Mercedes Bustamante, Universidade de Brasilia, Brazil; Eric Davidson, Woods Hole Research Center, USA; Scott Goetz, Woods Hole Research Center, USA; Richard Houghton, Woods Hole Research, USA; Michael Keller, National Ecological Observatory Network, USA; Simon Lewis, Leeds University, UK; Thomas Lovejoy, Heinz Center for Science, Economics and the Environment, USA; Patrick Meir, University of Edinburgh, UK; Paulo Moutinho, Instituto de Pesquisa Ambiental da Amazonia, Brazil, and Woods Hole Research Center, USA; Carlos Nobre, Centro de Previsao de Tempo e Clima—CPTEC, Brazil; Scott Ollinger, University of New Hampshire, USA; Oliver Phillips, Leeds University, UK; George Woodwell, Woods Hole Research Center, USA.

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Jeremy Hance
mongabay.com (March 19, 2010).

Scientists: new study does not disprove climate change threat to Amazon.