Climate scientists: Brazil’s rainforests have begun to release carbon dioxide, not absorb it

Climate scientists have found that Brazil’s rainforests in 2013 began to emit more carbon dioxide than they absorb. The article, with its conclusions, was published by the scientific journal Science Advances.

“Rainforests play a crucial role in carbon dioxide fixation, but no one has tried to accurately assess how this process is affected by trees growing outside the Amazon. Our observations have shown that the amount of carbon stored in them is gradually decreasing. This is due to both a decrease in the rate of CO2 uptake and an increase in its emissions,” the researchers write.

The Amazon rainforest covers about 5.5 million km2 and contains 10% of the carbon stored in all living organisms on Earth. In addition to them, there are many other forest areas in Brazil and other Latin American countries. They are just as intensively cut down as the Amazon forests, but these forests’ state is almost not studied.

Climate scientists and ecologists, led by Professor Rubens Manuel dos Santos of the Federal University of Lavras (Brazil), have filled this scientific knowledge gap. In a new study, researchers found out how the biomass of 32 similar rainforests in Brazil changed between 1987 and 2020.

Scientists were interested in how the increase in atmospheric CO2 concentration and the rate of biomass recruitment were related and how other climatic and anthropogenic factors, including reduced precipitation, periodic droughts, and deforestation, reduced the amount of carbon stored in these forests.

To do this, scientists collected samples of wood and soil in the rainforests of Brazil. Also, they tracked how the average temperature and precipitation level changed in these regions of the country. Using this data, climatologists made long-term estimates and predictions about the rate at which trees absorbed CO2 and released it.

These measurements showed that until about 2013, most of Brazil’s rainforests outside the Amazon absorbed more carbon dioxide than they released. Thanks to this, they gradually increased their biomass. Subsequently, everything went the other way around, and now every year, forests lose about 130 kg of carbon per hectare of area.

Dos Santos and his colleagues found that these losses were associated with both a decrease in the amount of CO2 absorbed and an increase in its emissions into the atmosphere. The first indicator decreases by 2.6% every year, and the second one grows by 3.4%. According to climatologists, semi-deciduous rocks were less affected by these processes, and evergreen forests were most affected by them.

The researchers ‘ calculations show that the main driver of these losses was the decrease in precipitation in all regions of Brazil (each year it falls by about 10 mm), as well as periodic heatwaves and associated droughts. Also, scientists do not exclude the fact that some of these losses may be due to a kind of competition between trees and lianas for access to water and light.

Climate scientists expect that such trends will increase even more in the coming years and decades — as temperatures and co2 concentrations in the air increase. This could further accelerate the escape of carbon dioxide from Brazil’s rainforests. This should be taken into account both in the development of climate models and in the development of measures aimed at saving South America’s forests from degradation, the researchers concluded.

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