An extreme drought and prolonged heatwave in 2023 pushed parts of the Amazon rainforest from being a crucial carbon sink to becoming a temporary carbon source, releasing between 10 and 170 million tonnes of carbon dioxide into the atmosphere over three months, according to a new study.
The research, published in American Geophysical Union’s journal AGU Advances, warns that ocean-driven warming and persistent dryness may be undermining the Amazon’s ability to absorb carbon faster than previously expected a shift with serious implications for global climate stability.
Between September and November 2023, the rainforest emitted more carbon than it absorbed, contributing up to 30 per cent of the total net carbon loss across tropical land that year. Scientists say unusually high sea surface temperatures in both the Atlantic and Pacific oceans drove regional temperatures to more than 1.5°C above pre-industrial levels, disrupting the Amazon’s carbon cycle.
Ocean Warming Triggered Severe Dryness
Researchers linked the carbon release to warmer ocean waters that reduced moisture transport from the Atlantic to South America, creating unusually dry atmospheric conditions across the Amazon basin during the latter half of 2023. The combined stress of extreme heat and water scarcity weakened vegetation’s ability to carry out photosynthesis.
To assess the rainforest’s carbon balance, scientists used atmospheric carbon dioxide measurements, satellite remote sensing, computer simulations through Dynamic Global Vegetation Models and flux data from the Amazon Tall Tower Observatory (ATTO). The multi-layered analysis showed a clear shift: the Amazon moved from being a carbon sink to a weak carbon source by May, with emissions peaking in October.
Importantly, the carbon loss was not primarily driven by fires. Although the fire season extended into November, the number of fires remained within the normal range observed over the past two decades. Instead, the dominant factor was reduced vegetation uptake plants absorbing less carbon due to drought stress.
The study notes that total carbon losses for 2023 would have been even higher without a strong early-season recovery. Between January and April, above-average rainfall in the northern Amazon boosted vegetation growth and carbon absorption, partially compensating for the losses later in the year.
However, the temporary recovery was not enough to prevent a net annual carbon deficit. Susan Trumbore, head of the ATTO project in Germany, stated that the anomalous carbon release in 2023 was largely due to weakened vegetation uptake rather than increased fire emissions.
The findings raise concerns that the Amazon rainforest long regarded as one of the planet’s most important carbon sinks may be edging closer to a long-term transition into a net carbon source. While strong El Niño events can intensify drought conditions, the researchers emphasised that broader ocean warming beyond the Pacific also played a significant role.
If such ocean-driven warming continues, the Amazon’s resilience could decline more rapidly than climate models have projected, potentially accelerating global climate change and weakening one of Earth’s most critical natural buffers against rising greenhouse gas levels.