A study recently published in the journal Nature Geoscience, carried out by researchers from the University of São Paulo (USP), indicates that the weakening of the circulation chaise longue turnaroundAtlantic (AMOC) could reduce precipitation in the north of the Amazon and increase it in the south.
The AMOC is a system of ocean currents that carries warm surface waters north and cold waters south into the depths of the Atlantic. It is essential for the global climate because it distributes heat throughout the climate system, affecting the location of precipitation and regulating temperatures in various regions of the planet.
The study showed that the weakening of this important current will reduce rainfall in the Amazon in an already intensely deforested region, such as the south and east. The preserved regions of the north, on the other hand, would be most affected by drought. This imbalance could further compromise the sustainability of the forest.
Marine sediments reveal impact of past climate changes
By analyzing samples of marine sediments containing traces of pollen and microcharcoal that arrived at the mouth of the Amazon thousands of years ago, scientists managed to reconstruct a critical climatic period called HS1 (between 18,000 and 14,800 years).
During HS1, a period of natural global warming that occurred in the past, melting glaciers in the Northern Hemisphere released large amounts of fresh water into the Atlantic, temporarily interrupting the AMOC. This collapse caused the Amazon’s tropical rain belt to shift southward, leaving the north drier. This created expanses of savannah in the forest region, with drier vegetation.
What can we expect from the future?
Based on these past observations, the researchers used numerical climate models to simulate a scenario in which the current AMOC weakens by about 50%. The result is that, just as in HS1, the tropical rain belt has moved south, leaving the northern Amazon drier and the south wetteras shown in the figure below, on the left.
The problem is that the south and east of the Amazon are the regions most affected by deforestation (figure above, right – source: Instituto Nacional of Space Research-INPE), which limits the areas where the forest could expand to adapt to the new precipitation regime. In the words of Professor Cristiano Chiessi, one of the authors of the study:
This is the big risk: the combination of climate change and changes in land use. What is the point of a drop in precipitation in the north offset by an increase in the south, if it is in this region that deforestation reigns? This combination could lead to irreversible degradation of the forest.
And according to the latest studies, When could AMOC collapse? It is not yet possible to determine precisely, but there are indications that the system is already losing strength. Greenland’s ice cover is melting rapidly, and this release of fresh water into the Atlantic poses a real threat d’weakening of the AMOC over the course of the century.
Without this circulation, the transport of water masses between the north and south of the Atlantic will be interrupted or will occur much more slowly, which will affect the transport of heat in the ocean and will have serious consequences for the entire climate system, like those described in this article for the Amazon region.
Article reference:
Akabane, T.K., Chiessi, C.M., Hirota, M. et al. (2024) Weaker Atlantic overturning circulation increases the vulnerability of northern Amazon forests. Nat. Geosci.
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