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Emissions of carbon dioxide—the most abundant greenhouse gas—double in the Amazon

Study indicates that increased deforestation resulted in the rainforest emitting more carbon than it absorbed in 2019 and 2020

Burnt forest near Porto Velho in August 2019

Bruno Rocha / Fotoarena / Folhapress

A trend that had been growing since the middle of the last decade has now become a reality in all four corners of the Amazon: the largest rainforest on the planet is no longer a carbon sink and is now a source of carbon in the atmosphere. This means that carbon dioxide (CO2), the main gas responsible for global warming, far surpassed absorption in all of the biome’s major subregions. From north to south, from east to west, the ecosystem now emits more CO2 than its plants can capture.

According to a recent study, the results of which were published as a preprint (a paper yet to be peer reviewed by a scientific journal) on Research Square on September 19, the carbon emissions surplus in the Amazon in 2019 and 2020 was double the annual average of the previous nine years, from 2010 to 2018. More carbon in the atmosphere in the form of CO2 and methane (another greenhouse gas) raises the planet’s temperature and intensifies climate change. The level of carbon dioxide in the Earth’s atmosphere has increased by almost 50% since the mid-nineteenth century, while the planet’s average temperature has risen by 1.1 degrees Celsius (ºC).

“This increase in emissions was caused by the fact that in these two years, the west of the Amazon also became a significant source of carbon dioxide, as had already occurred with the east,” says Luciana Gatti, head of the Greenhouse Gases Laboratory of the Brazilian National Institute for Space Research (INPE) and lead author of the article. “Previously more concentrated in the south of Pará and the north of Mato Grosso, in an area historically known as the ‘arc of deforestation,’ the clearing of native vegetation has now spread to the south of Amazonas, Acre, and Rondônia.” Thirty other scientists from Brazil and abroad were named as authors of the paper, which is in the process of being accepted for publication in an international scientific journal.

Alexandre Affonso

Scholars of deforestation nicknamed the region that covers these three Amazonian states as Amacro. Referencing the first two letters of each state, the name follows the same pattern as Matopiba, an acronym used to describe a frontier of agriculture and deforestation in the Cerrado (a wooded savanna biome) that includes the states of Maranhão, Tocantins, Piauí, and Bahia.

To date, roughly 20% of the Brazilian Amazon has been deforested, according to INPE data. Since INPE’s Project for Satellite-Based Deforestation Monitoring in the Legal Amazon (PRODES) began providing data on the official rate of deforestation in the region in 1988, Pará and Mato Grosso have lost more native vegetation than any other states. Together, they account for about two-thirds of all deforestation over the last three decades. In 2021, Amazonas became the second most deforested state for the first time, with more native vegetation cleared than in Mato Grosso—at 2,300 square kilometers (km2) compared to 2,200 km2. Pará remained in first place with 5,200 km2 of vegetation cut down.

The Amazon’s transition from carbon sink to source was completed at the turn of this decade. During this period, the emissions surplus in the carbon balance—which takes into account all CO2 absorption and emission processes, whether natural or manmade—in the entire Amazon doubled. According to the new study, the biome released 0.09 grams (g) of carbon into the atmosphere more than it absorbed per km2 every day between 2010 and 2018. In 2019, the daily emissions surplus was 0.17 g. In 2020, it rose to 0.20 g.

Bruno Kelly / Reuters / FotoarenaAerial view of deforested area around a road in Apuí, southern Amazonas, in September 2021Bruno Kelly / Reuters / Fotoarena

In the west of the Amazon, which remains more preserved than the east despite being under increasing environmental pressure, the carbon emissions surplus was up to four to 10 times greater in 2019 and 2020 than the historical average in some subregions (see graph). “There was no major climate anomaly in these two years that would explain this increase in emission levels. The recent rise in deforestation and fires and the dismantling of environmental oversight are behind this increase in carbon emissions in the biome,” says Gatti. “A similar volume of carbon was emitted in 2019 and 2020 as during the great Amazonian drought of 2015–2016, when there was a record-breaking El Niño.”

Characterized by warming surface waters in the South Pacific Ocean, the El Niño phenomenon temporarily alters the climate in various parts of the world. In the Amazon, it usually increases temperatures and causes prolonged droughts, reducing the biome’s ability to absorb carbon from the atmosphere.

The article also highlights that the amount of rainforest destroyed by fires—which go hand in hand with deforestation—increased by 42% in 2020 over the annual average for 2010–2018. “The number of active fires detected in the Amazon by satellite over the course of a year is currently around 20,000, double the standard of 10 years ago,” says Alberto Setzer, a researcher with INPE’s Queimadas program and coauthor of the article. The paper also points out that in 2019 and 2020, the number of summons issued for deforestation and environmental crimes fell by 42% and fines fell by 89% compared to the first eight years of the decade.

Alexandre Affonso

“The situation is very worrying,” warns climatologist Carlos Nobre, a senior researcher at the Institute for Advanced Studies at the University of São Paulo (IEA-USP) who participated in the study. “As well as putting the region’s rich biodiversity at risk, deforestation in the Amazon makes it more difficult to meet the targets of the Paris Agreement.”

Drafted with the support of the United Nations, the international treaty was signed in 2015 by almost 200 countries, including Brazil. Its objective is to reduce greenhouse gas emissions with the aim of limiting global warming to a maximum of 1.5 ºC above preindustrial levels from the mid-nineteenth century. This is theorized as the maximum rise in the planet’s average temperature that would still allow human societies to adapt to climate change and adequately mitigate its effects.

The problem is that the current situation in northern Brazil does not look promising. Since 2015, the official deforestation rate in the Amazon, as calculated by the INPE PRODES program, has risen every year. In 2019, it reached 10,000 km2 deforested in the year, a figure not recorded since 2008. Last year, it passed 13,000 km2 and the upward trend is continuing (see graph). Several deforestation records were broken in the early 2000s, with more than 25,000 km2 cleared in two consecutive years: 2003 and 2004. The adoption of new public policies successfully reduced the problem to its lowest levels at the beginning of last decade, when the Amazon lost approximately 5,000 km2 of vegetation cover per year. But in 2016, deforestation began to rise again.

Bruno Kelly / Reuters / FotoarenaCattle on a pasture in Rio Pardo, north Rondônia, in September 2019Bruno Kelly / Reuters / Fotoarena

“Until 2018, Amazonas was the fourth most deforested state in the region behind Pará, Mato Grosso, and Rondônia [which is six-and-a-half times smaller than Amazonas],” says remote-sensing specialist Claudio Almeida, head of the INPE’s Amazon and Other Biomes Monitoring Program and a coauthor of the article by Gatti and colleagues. “Now it is second after only Pará, which historically is the state where the most native vegetation is cleared every year. The recent dismantling of environmental oversight has encouraged more deforestation.”

With growing holes in vegetation cover and its southern margins degraded by advancing deforestation, wildfires, and the establishment of new pasture areas, the Amazon has lost some of its capacity to remove carbon from the air and to act as a counterbalance to climate change. Spread across nine countries in South America with a total area of 7 million km2, of which about 60% is in Brazilian territory, the planet’s largest rainforest, despite facing growing pressure, still represents an enormous patch of green on the world map. “A considerable proportion of the biome’s native vegetation in Brazil is still preserved,” points out Marcos Rosa, technical coordinator of MapBiomas, a collaborative network comprised of NGOs, universities, and technology startups.

Rosa was not part of the team that carried out the new carbon balance study, but data from the most recent annual MapBiomas survey on land use and land cover in the Brazilian Amazon corroborate the scenario described in the paper by Gatti and colleagues. According to the survey, published in September, livestock areas in the Amazon tripled between 1985 and 2021, now representing 13% of the biome in Brazil. The official data indicate that the total number of cattle in the country, currently at 220 million, is increasing in the Legal Amazon and decreasing everywhere else. The amount of land occupied by agricultural crops, primarily soy, is just 2% of the total.

Alexandre Affonso

“Deforestation is a speculative, unplanned approach used with the hope of gaining legal possession of a deforested area. Clearing a pasture and placing cattle on it is the fastest and cheapest way to occupy a recently deforested region, which was almost always previously public land,” explains Rosa. Soy farming may eventually replace this new pasture if the newly occupied deforested land is legalized and ownership granted to the occupant through amnesty and pardon processes approved by the authorities. “This process often takes years. Soy is grown on large properties in the Amazon and the farmers need credit from the bank to run their operations. But banks only lend money to legal landowners,” says Rosa.

Deforestation is also stimulated by the creation, expansion, and revitalization of roads, such as the BR-319 highway that connects Manaus and Porto Velho. According to PRODES data, the Amazonian municipality of Lábrea, in the south of the state, close to the border with Acre and Rondônia, is the fourth most deforested in the Amazon. With less than 50,000 inhabitants, Lábrea has lost 3,000 km2 of vegetation since 2008, surpassed only by Altamira and São Félix do Xingu in Pará and Porto Velho, the state capital of Rondônia. The only way to access it by land is via the final stretch of the Trans-Amazonian Highway.

Natural and anthropic factors alter the carbon balance of a region, meaning how much carbon dioxide it emits and absorbs. There is really only one process capable of removing significant amounts of CO2 from the atmosphere: photosynthesis, an essential mechanism to the growth and survival of plants. These plants may live above the ground, such as the trees in the Amazon rainforest, under the soil, or in rivers and the sea (algae). In terms of emissions, the scenario is more complex. The burning of fossil fuels—such as oil, natural gas, and coal—and loss of plant biomass lead to the release of both carbon dioxide and carbon monoxide (CO). Plant respiration and the decomposition of organic material also emit CO2.

Over the last few decades, as concern about the carbon balance and global warming has grown, forests have been identified as major absorbers of atmospheric CO2. Once inside the plants, the carbon is converted into sugars and stored as biomass (roots, stems, and leaves). It only returns to the atmosphere when the plant dies and is slowly decomposed by insects, bacteria, and fungi. Forest fires also cause the carbon in plant biomass to be returned to the air—but much more abruptly and immediately. This cycle feeds back into and stimulates global warming.

Alexandre Affonso

Previous studies by Gatti’s group, published in 2014 and 2021, had already shown that the Amazon as a whole was becoming a carbon source. But the driving force behind the change was the eastern region, where deforestation has historically been more of a problem. Depending on the year, the better-preserved western region acted as a carbon sink, was neutral (emissions equal to absorption), or was a slight but not clear source of carbon, within the margin error in the studies in question. Since 2019, however, the figures have become more robust and there is little doubt that the western Amazon has followed the same path as the east.

There is no shortage of scientific literature showing that the Amazon has been getting hotter and drier in recent years, such as a paper by climatologist José Marengo of the Brazilian Center for Natural Disaster Monitoring (CEMADEN) and INPE researchers (see Pesquisa FAPESP issue nos. 249 and 285). One of the consequences of the temperature increase and prolonged droughts is a reduction in the amount of water in the rainforest. For example, the most recent MapBiomas survey highlights that the area covered by water in the region has decreased by 14.5% in the last 20 years. Since some of the water in the Amazon is transported to the Brazilian Midwest and Southeast, a drier northern region tends to result in less rainfall in other parts of the country.

The new data on the carbon balance in the Amazon are from an ongoing 12-year project coordinated by Gatti and funded by FAPESP. Since 2010, a small plane has flown over four locations in the rainforest every two weeks, collecting vertical atmospheric profiles from between 300 meters and 4.4 km above sea level. The four locations are located in different regions of the biome: Alta Floresta, Mato Grosso, in the southeast of the rainforest; Rio Branco, Acre, in the southwest; Santarém, Pará, in the northeast; and Tabatinga, Amazonas, in the northwest. The chemical composition of the air samples is analyzed and used to calculate whether each area is emitting or absorbing more carbon. “This methodology allowed us to publish three articles in the journal Nature: two on carbon dioxide and one on methane. It’s a well-established approach,” says the chemist.

Carlos Nobre believes that although the current trend toward the Amazon acting as a carbon source instead of a sink is disturbing, it could be reversed in a short time if deforestation is reduced over the next few years, or even just reduced to low levels of around 5,000 km2 per year. “Secondary forest grows quickly and helps remove carbon from the atmosphere,” explains the climatologist. Secondary forest is the term for vegetation that spontaneously sprouts and regenerates in abandoned, unused deforested areas. It is not as dense and rich as intact forest, but the plants perform photosynthesis and feed on CO2. According to the most recent MapBiomas survey, around 4% of vegetation cover in the Amazon was formed in 2019 by secondary vegetation, equal to around 130,000 km2.

Interannual variation of Amazon Basin greenhouse gas balances and their controls in a warming and increasingly variable climate – CARBAM: the Amazon carbon balance long-term study (nº 16/02018-2); Grant Mechanism Thematic Project; Program Research into Global Climate Change; Principal Investigator Luciana Gatti (INPE); Investment R$4,940,200.83.

Scientific articles
GATTI, L. V. et al. Amazon carbon emissions double mainly by dismantled in law enforcement. Research Square. Online (preprint). Sept. 19, 2022.
GATTI, L. V. et al. Amazonia as a carbon source linked to deforestation and climate change. Nature. July 15, 2021.