From: Editor, ENN
Published October 22, 2013 09:52 AM

Amazon at more risk for dieback than previously thought

With habitat destruction trends and interaction with climate change, things are not looking good for the Amazon rainforest. According to a new study, the southern portion of the Amazon rainforest is at a much higher risk of dieback due to stronger seasonal drying than projections made by the climate models used in the latest report by the Intergovernmental Panel on Climate Change (IPCC).

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One of the biggest culprits? Drought.

Using ground-based rainfall measurements from the past three decades, a research team led by Rong Fu, professor at The University of Texas at Austin's Jackson School of Geosciences, found that since 1979, the dry season in southern Amazonia has lasted about a week longer per decade. At the same time, the annual fire season has become longer. The researchers say the most likely explanation for the lengthening dry season is global warming.

"The dry season over the southern Amazon is already marginal for maintaining rainforest," says Fu. "At some point, if it becomes too long, the rainforest will reach a tipping point."

If severe enough, the loss of rainforest could cause the release of large volumes of the greenhouse gas carbon dioxide into the atmosphere. It could also disrupt plant and animal communities in one of the regions of highest biodiversity in the world.

The new results contrast with forecasts made by climate models used by the IPCC. Even under future scenarios in which atmospheric greenhouse gases rise dramatically, the models project the dry season in the southern Amazon to be only a few to 10 days longer by the end of the century, and therefore the risk of climate change-induced rainforest dieback should be relatively low.

"The length of the dry season in the southern Amazon is the most important climate condition controlling the rainforest," says Fu. "If the dry season is too long, the rainforest will not survive."

The Amazon rainforest normally removes the greenhouse gas carbon dioxide from the atmosphere, but during a severe drought in 2005, it released 1 petagram of carbon (about one-tenth of annual human emissions) to the atmosphere. Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate of recent decades, the Amazon drought of 2005 could become the norm rather than the exception by the end of this century.

The report appears this week in the journal Proceedings of the National Academy of Sciences.

Read more at the University of Texas.

South America vegetation map image via Shutterstock. 

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