S. American Rain Cycle Nears "Critical Destabilization"; Impacts Expected Far Beyond Amazon

[hatrack]

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Using past observations and computer modelling, it finds that the Amazon and the South American monsoon are “one coupled system”, in which the evapotranspiration by the tropical rainforest recycles moisture from the Atlantic Ocean so that it can move south across the continent. Human degradation of the Amazon – by land clearance, fire, logging and mining – is pushing that system towards a tipping point, after which drier conditions would be expected to cause an abrupt “regime shift” in the rainforest, which would be unable to sustain itself and transport moisture.

Other biomes in the region would also be affected, along with swathes of agricultural land because the monsoon stretches thousands of miles south from the Amazon to the River Plate (Rio de la Plata) basin. There would also be a climate impact because the Amazon – which would be worst affected – has historically served as an important carbon sink, though another study this week suggests it is now so degraded that it is at best carbon neutral. A dieback of the forest would release enormous amounts of carbon.

The researchers on the Amazon-monsoon paper saw several precursors of the tipping point, including falling rainfall in many areas, the steady lengthening of the Amazon dry season, reduced soil moisture and the increasing frequency and intensity of droughts. There have been three statistically one-in-100-year droughts in the space of a single decade. “It is shocking to see these signs of destabilisation,” said the lead author, Nils Bochow, of the University of Tromsø and the Potsdam Institute of Climate Impact Research. “But we shouldn’t lose hope. We can still act. We need stricter rules regarding the rainforest.”

Global heating is adding to the pressure on the forest. Not included in their paper because it is too recent is this year’s fierce dry season, during which many Amazon rivers have fallen far below their average for this time of year, leading to navigation problems, water shortages and mass mortalities of dolphins and fish. Previous studies have suggested a tipping point could be reached when 20% to 30% of the Amazon is cleared, though there is considerable uncertainty about exactly where the point might be. Currently, between 17% and 26% of the rainforest has been destroyed and at least that has been degraded.

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https://www.theguardian.com/environment/2023/oct/04/south-american-monsoon-heading-towards-tipping-point-likely-to-cause-amazon-dieback

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