Risk of Amazon Rainforest Dieback Higher Than Predicted: Dangers of Climate Change

The Amazon Rainforest is one of the most species rich locations in the world. Now, though, scientists have discovered that this ecological hotspot may be facing new dangers from climate change. It turns out that the southern portion of this rainforest is at a much higher risk of dieback due to stronger seasonal drying than predicted in the past. If severe enough, this drying could release large volumes of greenhouse gas carbon dioxide into the atmosphere and disrupt one of the regions with the highest biodiversity on Earth.

In order to learn exactly how climate change might impact the Amazon rainforest, the researchers used ground-based rainfall measurements from the past three decades. They 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 also become longer. This could have major implications for the region.

More surprising, though, is the fact that these new findings fly in the face of 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. Yet it turns out that isn't the case; it looks like it will be far longer.

So what might be causing this longer dry season? The most likely reason behind these drier conditions is human-caused greenhouse warming, which inhibits rainfall in two ways. First, it makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above. Second, it blocks cold front incursions from outside the tropics that could trigger rainfall.

"The length of the dry season in the southern Amazon is the most important climate conditions controlling the rainforest," said Rong Fu, one of the researchers, in a news release. "If the dry season is too long, the rainforest will not survive."

As climate change continues to sweep the globe, it's more important than ever to understand exactly how it will affect biodiverse areas such as the Amazon. Learning how dry seasons might affect the region could allow conservationists target keys areas to protect. In addition, it shows exactly how great the impact of climate change can really be.

The findings are published in the journal Proceedings of the National Academy of Sciences.