The 1,200-mile Tapajós River cuts through the Amazon rainforest in Brazil, forming a basin where one-third of the world’s soy is produced. Satellite imagery reveals how the production of soy leaves scars on the once lush landscape. Trees are cut, and carbon dioxide is released.
The Lower Tapajós region is home to only 1.2 percent of the Brazilian Amazon, but new research suggests vegetation loss and subsequent carbon emissions are spiraling toward an alarming new reality.
Scientists report that in recent years, the Amazon has shifted from one of the world’s largest carbon sinks to one of its greatest polluters. While their research is grim, the study team also points to two mitigation techniques: curbing illegal logging and improved fire management.
These findings were published Monday in the journal Proceedings of the National Academy of Sciences (PNAS).
What you need to know first — The Amazon has long been considered an important carbon sink: Historically, its forests stores more carbon dioxide than they emit, helping reduce the impact of global warming. A 2018 study suggests the Amazon stores roughly 10 percent of the world’s forest carbon.
However, in 2015 scientists started to notice a stark trend: the Amazon is storing less and less carbon. What’s worse? It’s releasing carbon more into the atmosphere.
Case in point: A Nature study published in July found the Amazon’s role as a carbon sink is declining “as a result of factors such as deforestation and climate change.” That study team found the Amazon is releasing 0.3 billion tons of carbon into the air each year.
But until now, scientists haven’t known how climate changes and human deforestation intersect to make the Amazon a polluting hub. That’s where this new study emerges as a clue, offering insights through its examination of the effects of the 2015-16 El Niño-driven drought on the Amazon, in conjunction with human changes like deforestation.
How the discovery was made — Researchers analyzed the Amazon’s Lower Tapajós region, which was hit hard by the 2015-16 El Niño. This is a seasonal weather event that occurs when warm weather in the Pacific Ocean causes often unpredictable climate changes.
El Niño led to a significant drought in the region. The study team, in turn, wanted to understand the long-term effects of the drought, along with forest fires, in the Lower Tapajós.
The researchers studied undisturbed forests in the area, along with land where human deforestation took place between 2015 and 2018.
This allowed the study team to determine how ecological factors like drought and fires contributed to forest loss and carbon emissions in the area. Specifically, the researchers used statistical models to analyze the number of plant stems that died during this period.
Finally, the researchers scaled up their results to draw conclusions about overall carbon emissions and forest loss in the entire Amazon Basin.
What’s new — The scientists made four key findings:
- The 2015-16 El Niño killed more than 2.5 billion plant stems, releasing nearly 500 teragrams of carbon dioxide. (One teragram equals roughly 1,000,000 tons.)
- The effects were long-term: Tree death remained higher than pre-El Niño levels for three years in drought-affected forests and 30 months in forests affected by wildfires. New plant growth after the drought offset 37 percent of the increased emissions.
- Human deforestation made it worse: The researchers found “human disturbance significantly increased plant mortality” in forests in the region.
- Wood density had the largest effect on whether or not plants died in areas where forest fires occurred. Loggers often cut down trees with more dense wood for their timber value, further compounding this ecological devastation.
The researchers conclude that the Amazon is changing from a carbon sink that could save the planet into a massive basin that could actually increase the effects of global warming, writing:
“With more frequent droughts expected in future, forests of Amazon may lose their role as a robust sink of carbon, leading to a significant positive climate feedback and exacerbating warming trends.”
In combination with the effects of unnatural deforestation, climate fluctuations have the potential to dramatically contribute to forest loss in the Amazon, the study suggests. Increasing forest loss, in turn, can change the Amazon from a place of refuge to a site of crisis.
The study team argues for the development of long-term models, designed to analyze how drought, fires, and human disturbances, influence the region’s ability to function as a carbon sink.
Deforestation in the region surged to a 12-year high, according to a 2020 report. Bolsonaro is now asking for billions of dollars in aid to curb deforestation in the Amazon, which has already led to 430,00 acres of cut rainforest in 2021.
What’s next — While the findings are somber, it's possible the Amazon can be restored.
“While the next El Niño cannot be avoided, further human disturbance” to the forest can be avoided through two key steps, the study team writes. These are:
- Curbing illegal logging in the Amazon. Recent reports suggest using satellite technology and working with local indigenous communities could stem the tide of deforestation.
- Investing in improved fire management training.
Abstract: With humanity facing an unprecedented climate crisis, the conservation of tropical forests has never been so important–their vast terrestrial carbon stocks can be turned into emissions by climatic and human disturbances. However, the duration of these effects is poorly understood, and it is unclear whether impacts are amplified in forests with a history of previous human disturbance. Here, we focus on the Amazonian epicenter of the 2015–16 El Niño, a region that encompasses 1.2% of the Brazilian Amazon. We quantify, at high temporal resolution, the impacts of an extreme El Niño (EN) drought and extensive forest fires on plant mortality and carbon loss in un-disturbed and human-modified forests. Mortality remained higher than pre-El Niño levels for 36 mo in EN-drought–affected forests and for 30 mo in EN-fire–affected forests. In EN-fire–affected forests, human disturbance significantly increased plant mortality. Our investigation of the ecological and physiological predictors of tree mortality showed that trees with lower wood density, bark thickness and leaf nitrogen content, as well as those that experienced greater fire intensity, were more vulnerable. Across the region, the 2015–16El Niño led to the death of an estimated 2.5±0.3 billion stems, resulting in emissions of 495±94 Tg CO2. Three years after the ElNiño, plant growth and recruitment had offset only 37% of emissions. Our results show that limiting forest disturbance will not only help maintain carbon stocks, but will also maximize the resistance of Amazonian forests if fires do occur.*