Amazon released an estimated 10 to 170 million tonnes of carbon between September and November 2023
Extreme drought and heat linked to high Atlantic and Pacific sea surface temperatures
Carbon losses driven mainly by reduced vegetation uptake, not increased fires
Early-season rainfall partly offset annual emissions spike
Study warns rainforest could shift to long-term carbon source sooner than expected
Extreme drought and a prolonged heatwave in 2023 pushed parts of the Amazon rainforest from acting as a carbon sink to becoming a carbon source for three months, according to new research.
The paper has suggested that ocean-driven warming and prolonged drought could increasingly undermine the Amazon’s ability to absorb carbon — a shift that may accelerate global climate change.
The study, published in the journal American Geophysical Union (AGU) Advances, found that unusually high sea surface temperatures in both the Atlantic and Pacific oceans drove temperatures in the region to more than 1.5 degrees Celsius above pre-industrial levels. This shift disrupted the biogeographic Amazon’s carbon cycle.
The researchers said warmer ocean waters led to unusual atmospheric dryness across the region for the three months. Reduced moisture transport from the Atlantic to South America contributed to severe drought conditions during the second half of 2023, the study noted.
To assess the Amazon’s carbon balance at different spatial scales, scientists combined multiple data sources. These included atmospheric carbon dioxide measurements, eddy covariance flux data from the Amazon Tall Tower Observatory (ATTO), computer simulations using Dynamic Global Vegetation Models, and satellite remote sensing.
Between September and November, the Amazon shifted from being a carbon sink to a weak carbon source, releasing an estimated 10 to 170 million tonnes of carbon dioxide into the atmosphere.
The shift occurred despite an extended fire season lasting until November, rather than the usual October end. However, the number of fires recorded remained within the normal range observed over the past two decades (2003-2023).
The researchers attributed the 2023 carbon release mainly to reduced vegetation uptake — that is, weaker photosynthesis during the dry season — rather than increased emissions from fires.
They noted that net carbon loss for the year would have been higher without an unusually strong period of vegetation uptake earlier in the year, from January to April. Above-average rainfall in the northern Amazon is thought to have supported this early-season carbon absorption, partially offsetting losses that peaked in October.
“A stronger‐than‐normal vegetation uptake early in the year (January-April), consistent across data streams and spatial scales, mitigated the total carbon losses by the end of the year. We find a shift from carbon sink to source in May and a peak source in October,” the authors said.
They added that the weakened vegetation uptake contributed up to 30 per cent of the total net carbon loss across tropical land in 2023.
“We therefore attribute the anomalous carbon release in 2023 mostly to a weakened vegetation uptake, rather than increased losses from fires,” Susan Trumbore, head of the ATTO project in Germany, said in a press statement.
The authors concluded that the findings have wider implications for the global climate.
“Based on our findings, one key implication is that the Amazon may transition to a net carbon source more rapidly than previously projected. While strong El Niño events, like the one in 2023, can exacerbate this trend, our results and other studies also highlight the role of widespread ocean warming beyond the Pacific, suggesting that other factors in addition to ENSO contribute significantly to net carbon exchange in the region,” they wrote.