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Scientists Say 40% of Amazon Rainforest May Become Savanna

In August of last year, fires attributed to Brazilian agribusiness torched massive portions of the Amazon rainforest. The fires were emblematic of the rising destruction of the critical ecoregion and now, a team of scientists says much of that destruction may soon be irreversible. In fact, the scientists say their models show that up to 40% of the Amazon rainforest may cross a “tipping point” and become savanna later this century.

Scientists' model says that up to 40% of the Amazon jungle may soon become savannah.

Staal, A., Fetzer, I., Wang-Erlandsson, L. et al.

The team of scientists, led by environmental scientist, Arie Staal, recently published their findings in the journal, Nature Communications. Staal et al. came to their conclusions based on running simulations in which tropics across Africa, the Americas, Asia, and Australia began with no forests, and then developed them over time. They also ran simulations in which rainforests entirely covered the tropical regions of Earth, and then diminished over time.

In the former simulation category, the scientists watched as forests emerged over time; this, in turn, allowed them to glean the minimum forest cover possible in the tropics. In the latter category, the scientists observed an unstable scenario; one in which the regions that can’t support rainforest lost it thanks to their lack of moisture.

By modeling these two scenarios, the scientists aimed to develop a sense of the Amazon rainforest’s resilience. That is, the capacity of the ecosystem to bounce back from a serious perturbation, and maintain its essential characteristics.

“As forests grow and spread across a region, this affects rainfall,” Stall, formerly at the Stockholm Resilience Centre at Stockholm University, said in a recent report from The Guardian. “Forests create their own rain because leaves give off water vapour and this falls as rain further downwind,” the scientist added.

Scientists' model says that up to 40% of the Amazon jungle may soon become savannah.

Staal, A., Fetzer, I., Wang-Erlandsson, L. et al.

Once the team approximated the Amazon’s resilience, it was able to determine that, as climate conditions stand, the rainforest could—likely—partially recover from complete deforestation. Although the team says that later this century, it may lose that ability.

Immediately above, the shifts in forest potential between recent climates and those likely to occur later this century are shown. Red areas are stable forest now, but may cross the tipping point to savanna later this century. Blue areas, conversely, are too dry to maintain forest now, but may be able to later this century. The green and beige areas show maximal and minimal forest distribution respectively.

Scientists' model says that up to 40% of the Amazon jungle may soon become savannah.

Neil Palmer/CIAT

“In around 40 percent of the Amazon, the rainfall is now at a level where the forest could exist in either state – rainforest or savanna,” Staal added in a Stockholm University press release. Turning those regions back into forest should they shift “will take many decades” co-author Ingo Fetzer added.

The scientists also found that with higher growths in global emissions, more of the Amazon loses its resilience. I.e. the more global emissions, the more the Amazon dries out and becomes a savanna-type ecosystem.

“If we removed all the trees in the Amazon in a high-emissions scenario a much smaller area would grow back than would be the case in the current climate,” co-author Lan Wang-Erlandsson added. In the highest-emission scenario, the scientists say the smallest sustainable area of Amazon rainforest contracts by 66%.

Feature image: Neil Palmer/CIAT