Deforestation in the Amazon increases heat in the region by up to 4°C – 10/31/2023 – Environment

The global climate crisis is one of the reasons why the Amazon is getting hotter, but much of the region’s warming has local and regional origins, linked to the deforestation of the biome — and a study carried out by Brazilian and British researchers is the first to quantify the different contributions to this effect.

According to the analysis, which has just been published in the scientific journal PNAS, the increase in temperature in heavily deforested areas of the Amazon basin may have been up to 14 times higher than what would have happened if the forest had not been cut down. This corresponds to temperatures 4°C higher, or even more.

The work is signed by Edward Butt, from the University of Leeds, in the United Kingdom, and by Francisco Silva Bezerra, from Inpe (National Institute for Space Research), among other researchers.

They used satellite data that estimated the temperature of the Earth’s surface over a period ranging from 2001 to 2020, therefore encompassing a good part of the periods of greatest deforestation in the biome, in addition to the main phase of continuous reduction of this process, during the first Lula governments. and Dilma.

There was little doubt about the greater likelihood of a local temperature increase when forest areas are deforested. This had already been seen in the Amazon rainforest and other tropical forest areas around the world.

In an interview with Sheet, Butt explained that forest clearing has two contradictory effects on local temperatures. On the one hand, there is a change in albedo (roughly speaking, the ability of a surface to reflect or absorb sunlight). In general, forests, because they are darker, absorb more light than a plantation or pasture, for example. Looking only at this variable, therefore, the deforested area would tend to heat up less.

“But today we understand well the fact that the cooling associated with an increase in surface albedo is not enough to counterbalance other factors. The most important are the loss of evapotranspiration from the forest [que produz mais chuvas, por exemplo] and the irregularity of the forest surface,” he says. “The net result of these three factors is a warming of the surface linked to forest loss.”

One of the research’s doubts, however, was to what extent deforestation would also be able to affect these climatic factors on a regional scale (in the study, defined as the range that goes from 2 km to 100 km away from the deforested areas).

In theory, the warming effects of a “clear-cut” section of the forest could spread to other places in the Amazon through, for example, the movement of air masses and changes in rain clouds, but it was not clear until at what point this would actually occur.

The data collected by the Brazilian-British team indicates, firstly, that local and regional factors appear to be interacting. Generally speaking, the more deforestation, the more warming, which makes sense.

Areas with less than 10% forest loss warmed by just 0.3°C during the period studied, well below the average of 0.78°C for the entire Brazilian Amazon.

However, areas that experienced deforestation of the order of 10% to 20% warmed by 0.6°C (twice as much as undisturbed areas).

The number becomes triple if there is also this same level of deforestation on a regional scale (within a radius of up to 10 km). When there is up to 50% deforestation at a local and regional level (in this case, up to 100 km radius), the situation becomes decidedly hellish: 4.4°C increase in temperature.

In addition to this finding, the research also used machine learning analysis — a type of artificial intelligence — to try to find patterns in the impact of different types of deforestation on temperature.

Roughly speaking, machine learning works by “training” the computer program on a large mass of data that it can access at will. After this training phase comes the analysis of a subset of similar data, in which the patterns detected in the training sample are used to make predictions.

With this method, the researchers concluded that, to predict how the temperature of the Amazon region will evolve, both local and regional-scale deforestation (up to 100 km in radius) are important, reinforcing, once again, the evidence that they are interacting.

The possibility of this effect spreading more widely across the Amazon is not at all encouraging, not only because of its impact on human well-being but also because of the possible repercussions on factors such as rainfall and the survival of crops and livestock, whose tolerance to heat is not unlimited.