When the Rainforest Can't Breathe: How El Niño and Droughts Weakened the Amazon’s Carbon Recovery

Redacción HC
02/09/2024

The Amazon rainforest, long considered a crucial ally in fighting climate change, may be losing its edge. A new satellite-based study published in AGU Advances reveals that the Amazon basin struggled to recover its carbon balance after the 2015–2016 El Niño event. Despite expectations of a rebound, the forest failed to recapture nearly 0.6 gigatonnes of carbon (GtC) even by 2018.

The research, led by Junjie Liu and an international team of atmospheric and ecological scientists from NASA/JPL, Caltech, USDA, and other institutions, offers a stark warning: extreme drought and rising atmospheric dryness are weakening the Amazon’s ability to bounce back after climate shocks.

A Deeper Problem: Why the Amazon Is Still Losing Carbon

During the 2015–2016 El Niño, the Amazon basin experienced record heat, low rainfall, and widespread fires. These events caused a massive carbon release into the atmosphere. While such pulses are not new, what surprised researchers was the Amazon’s failure to recover its carbon balance by 2018—even after El Niño subsided.

The study examined whether this prolonged loss was linked to two critical stressors:

1. Atmospheric aridity – How dry the air is, which affects plant function.
2. Soil water deficit – How little water is stored underground to support vegetation.

Together, these conditions appear to have weakened photosynthesis across much of the basin, reducing the Amazon’s natural ability to absorb CO₂.

Remote Sensing and Modeling: How Scientists Measured the Forest's Carbon Health

Using data from Earth-observing satellites between 2015 and 2018, the team tracked:

• Net carbon exchange – The overall amount of CO₂ absorbed vs. emitted.
• Gross primary production (GPP) – A measure of photosynthetic activity.
• Fire-related emissions – Derived from thermal and optical satellite observations.

They divided tropical South America into four regions (northeast, southeast, west-south, and west-northwest) to assess local patterns of stress and recovery. These observations were then compared against climate-carbon models to identify deviations.

The researchers found that actual responses to drought and heat exceeded model predictions, particularly in the northeastern Amazon.

Key Findings: A Forest Losing Its Breath

1. The Amazon's Carbon Deficit Persists

Between 2015 and 2018, the northeastern Amazon alone lost nearly 0.6 GtC, without showing signs of full recovery. This amount of carbon is equivalent to annual emissions from over 150 million cars.

2. Photosynthesis Severely Suppressed

Photosynthetic rates dropped to levels three times lower than what historical drought sensitivities would predict. This suggests that current climate extremes are overwhelming the forest's adaptive capacity.

3. Biomes Responded Differently

• Humid Forests: Most carbon loss came from diminished photosynthesis, not fires.
• Savanna Regions: Fire emissions played a larger role in carbon flux disruptions.

4. No Fast Recovery

Contrary to previous studies, which assumed tropical ecosystems bounce back within two years, this study reveals longer-term impacts when drought is combined with high heat and dry air.

5. Models Need Revising

Current earth system models may underestimate the compounding effects of extreme aridity and deep soil moisture stress on forest resilience.

“The Amazon is not just a carbon sponge—it’s a living system that breathes,” said co-author Sassan Saatchi. “Right now, that breath is shallow and labored.”

Implications: What This Means for Climate Policy and Forest Management

A. Climate Mitigation Strategies Must Adapt

• Forest-based carbon offset schemes often assume fast post-drought recovery. This research suggests such assumptions may be flawed.
• Climate policy must account for longer recovery timelines and reduced carbon absorption potential during and after extreme events.

B. Need for Improved Forest Management

• Early-warning systems for drought and fire risk must be scaled up.
• Reforestation efforts must focus on native species adapted to water stress.
• Water conservation strategies (e.g., protecting riparian zones) are essential to safeguard photosynthetic function.

C. Scientific Recommendations

1. Integrate hydrological stress variables into climate models.
2. Pair satellite data with ground-based observations to validate ecosystem changes.
3. Reevaluate the carbon sink strength of tropical forests in climate projections.

D. Social Impact

• Indigenous and rural communities who rely on the forest for water, food, and cultural survival face heightened vulnerability.
• Long-term carbon loss could destabilize regional climate patterns, leading to more extreme weather and compounding socio-environmental risks.

Conclusion: A Sobering Climate Signal from the Amazon

The Amazon has long been viewed as a resilient carbon sink, capable of weathering droughts and fires. But this study shows that there are limits to that resilience, especially in a warming world where El Niño events may become more frequent and intense.

As carbon emissions rise globally, we must not assume that tropical forests will continue to absorb the damage. The Amazon’s slow recovery is not just an ecological concern—it’s a planetary warning. If the forest can no longer "breathe," neither can we.

Topics of interest

Climate