The southern part of the world’s largest forest is drying out and over the next century it may turn into a savannah.
The Amazon rainforest is a repository of biodiversity and the Earth’s green lungs. What the future holds for it? The two main threats of the 21st are deforestation and effects of climate change. The latter issue has been investigated by the international research team led by Professor Rong Fu from the University of Texas at Austin, USA. Their findings are worrying. The researchers believe that a large area of the Amazon rainforest, three times bigger than Poland, is endangered by drought. They estimated that the dry season there has been extending systematically for three decades, at a pace of approximately one week per decade. If this trend continues, the primeval forest with its abundant wildlife is facing extinction.
The area endangered by drought is located in the south-western part of Amazonia, i.e. close to the Cordilliera chain, but far from the Atlantic Ocean and relatively far from the equator. According to the research, the forest is still resilient to scarce rainfall, however, if crises similar to those of 1998, 2005 and 2010 will occur in the nearest future it may reach its tipping point – the more so as the longer the dry season, the more violent and frequent the forest fires. In the above-mentioned years, rainfall deficits were so serious that dying tree crowns could be seen even from remote sensing satellites. Instead of absorbing carbon dioxide, the Amazon rainforest released it into the atmosphere in large volumes. “Years like 2005 and 2010 may return in half a century, given that this part of South America remains prone to dry spells,” says Rong Fu. The scientist stressed, however, that the part of the forest closer and north to the Amazon river still receives enough rainfall and is not exposed to climate change so far.
This widening gap between the dry south and the wet north stems from climate change around the globe, researchers say. The southern part of the Amazon rainforest is situated farther from the zone of equatorial rains, which is slowly moving northward due to the increasing warming rate of the Northern Hemisphere. Climatologist Julian Sachs from the University of Washington in Seattle has even established the speed of this process at approximately 1.4 km per year, which would mean around 40 km within the next three decades. It’s seemingly not too much, but it’s enough to cause rain in the south of Amazonia to begin slightly later and stop slightly earlier. This allows for building up of a strong high-pressure area because of which clouds disappear, and along with them - all the hopes for rain.
Interestingly enough, the latest report of the Intergovernmental Panel on Climate Change (IPCC) from late September does not forecast any severe dieback of the Amazon rainforest due to raising temperatures around the world. It states that such risk exists, but it is really unlikely. In this respect, the previous report of 2007, by the same organisation, was more pessimistic. The researchers became more optimistic after watching the results of simulation carried out with improved climate models. However, Rong Fu points out that the models make poor regional-scale projections of precipitation, which is of key significance in the case of Amazonia – a rainforest without rain will not survive long. Another researcher, Dan Nepstad, a cofounder of the IPAM institute (Portuguese: Instituto de Pesquisa Ambiental da Amazônia), the biggest independent research organisation concerned with Amazonia and located in the Brazilian city of Belem, adds bitterly that the southern part of the Amazon rainforest may disappear even in spite of the heart-warming scenarios of IPCC – not because of climate change, but deforestation.
The findings of the Rong Fu research team were published this October in the “Proceedings of the National Academy of Sciences” journal.