Study Shows Global Climate Change Impacts Southern Amazon

A study carried out by researchers from Unicamp, the University of Leeds and other institutions in South America and Europe points out that trees in the south of the Amazon are becoming more prone to die due to drought. The research collected samples in the central-eastern portion of the Amazon, close to Manaus and Pará, in the south, in the Mato Grosso region, and in the west, including parts of Acre, Peru and Bolivia.

Originally, the southern region of the forest may suffer more from drought, as it shares borders with biomes such as the Cerrado and also with agricultural frontiers. In addition, in this portion, trees are more resistant to dry periods due to the production of biomass, driven by growth in low-fertile soils. In the study, the southern Amazon was also the region in which the authors found the greatest capacity for climate adaptation of trees.

However, despite previous resistance to dry weather, intensive deforestation and the effects of global warming contribute to the vulnerability of the area.

origin of drought
Droughts in the Amazon should not be analyzed in isolation, as major droughts have been happening since the early 2000s. This phenomenon in 2005, 2010 and 2020, for example, resulted from the warming of the Atlantic Ocean north of the Equator, driven by changes in global warming, which consequently induced droughts in the Amazon region.

Carlos Nobre, environmental scientist and senior researcher at USP’s Institute for Advanced Studies (IEA), explains how this happened. “It is a phenomenon associated with the decrease in the intensity of the thermohaline circulation of the Atlantic Ocean, which is becoming weaker due to a phenomenon of melting glaciers in Greenland. This fresh water, falling over there in the North Atlantic, is lighter, does not sink and transports less heat from the Equator to the North Atlantic.”

Coming to the Amazon, the intensified drought, when added to the deforestation of the region, disrupts the supply of rain and prolongs the dry season. “Throughout the southern Amazon, we have more than 35% of deforested and degraded areas. During the dry season, the Amazon recycles a lot of water, about 4.5 mm of water per day. There are 4.5 liters of water per square meter of forest. On the other hand, in very degraded pasture, it recycles a maximum of 1.5 mm. With that, there is less water vapor in the atmosphere, less rain during the dry season”, he adds.

Carbon
One of the purposes of tropical forests is to collect carbon from the atmosphere. In southern Amazonia, it was observed that trees subjected to water stress, felt in periods with less water supply, emit more carbon than they absorb. When droughts are longer lasting and more frequent, this behavior also becomes recurrent. “The southern Amazon has become a source of carbon, no longer a carbon sink, as most of the planet’s tropical forests are, which remove a third of all carbon dioxide emissions from human activities”, comments Nobre.

The Amazon rainforest stores a large amount of carbon in the soil, around 150 to 200 billion tons. Nobre explains that if we lose all this carbon to the atmosphere, the changes could be irreversible for global climate change: “It will become practically impossible to reach the goals of the Paris agreement and zero all greenhouse gas emissions”. Paulo Artaxo, specialist in Physics Applied to Environmental Problems and professor at the Institute of Physics at USP, adds: “It is a brutal amount of carbon that, if thrown into the atmosphere, will further intensify global warming, which is already becoming critical”.

The continent’s climate
In addition to the “recycling” of water mentioned by Nobre and carbon capture, the Amazon contributes to the climate of Brazil and South America by maintaining the temperature. In the forest canopy, for example, the temperature does not exceed 30ºC.

“A large part of the water vapor that enters the Atlantic Ocean exits south of the Amazon through the so-called flying rivers.” This flow has about 200 thousand cubic meters per second. “It is practically the same value that feeds all the rain systems in the south of the Amazon and the snow systems in the Andean countries. If we pass this point of no return, this degraded system will not be able to recycle water with this efficiency, it will greatly reduce the volume of flying rivers and affect the climate of a large part of South America”, clarifies the environmental scientist.

For Artaxo, global climate change will not take long to reach Brazil directly: “In the Amazon region, we may have a temperature increase of 4°C to 4.5°C”.