Low latency carbon budget analysis reveals a large decline of the land carbon sink in 2023 (2407.12447v1)

Abstract: In 2023, the CO2 growth rate was 3.37 +/- 0.11 ppm at Mauna Loa, 86% above the previous year, and hitting a record high since observations began in 1958, while global fossil fuel CO2 emissions only increased by 0.6 +/- 0.5%. This implies an unprecedented weakening of land and ocean sinks, and raises the question of where and why this reduction happened. Here we show a global net land CO2 sink of 0.44 +/- 0.21 GtC yr-1, the weakest since 2003. We used dynamic global vegetation models, satellites fire emissions, an atmospheric inversion based on OCO-2 measurements, and emulators of ocean biogeochemical and data driven models to deliver a fast-track carbon budget in 2023. Those models ensured consistency with previous carbon budgets. Regional flux anomalies from 2015-2022 are consistent between top-down and bottom-up approaches, with the largest abnormal carbon loss in the Amazon during the drought in the second half of 2023 (0.31 +/- 0.19 GtC yr-1), extreme fire emissions of 0.58 +/- 0.10 GtC yr-1 in Canada and a loss in South-East Asia (0.13 +/- 0.12 GtC yr-1). Since 2015, land CO2 uptake north of 20 degree N declined by half to 1.13 +/- 0.24 GtC yr-1 in 2023. Meanwhile, the tropics recovered from the 2015-16 El Nino carbon loss, gained carbon during the La Nina years (2020-2023), then switched to a carbon loss during the 2023 El Nino (0.56 +/- 0.23 GtC yr-1). The ocean sink was stronger than normal in the equatorial eastern Pacific due to reduced upwelling from La Nina's retreat in early 2023 and the development of El Nino later. Land regions exposed to extreme heat in 2023 contributed a gross carbon loss of 1.73 GtC yr-1, indicating that record warming in 2023 had a strong negative impact on the capacity of terrestrial ecosystems to mitigate climate change.

• The paper presents a rapid carbon budget analysis using DGVMs, satellite-based inversions, and model emulators to assess the 2023 decline in land carbon uptake.
• The paper finds that atmospheric CO₂ growth spiked to 3.37 ppm and the land sink fell to 0.44 GtC yr⁻¹, marking the weakest uptake in two decades.
• The paper identifies regional flux anomalies in the Amazon, Canada, and Southeast Asia, driven by droughts, fires, and climatic shifts such as El Niño.

Decline of the Land Carbon Sink: Insights from a Rapid Carbon Budget Analysis

The research presented addresses the significant decline of the global land carbon sink in 2023, providing a timely assessment of the global carbon cycle. This paper utilizes an integrative approach combining dynamic global vegetation models (DGVMs), satellite-based atmospheric inversions from OCO-2, and various biogeochemical model emulators to estimate oceanic and terrestrial carbon exchanges. Through these methodologies, the authors provide a comprehensive analysis to interpret the record-high atmospheric CO₂ growth rate and the dynamics of carbon sinks within the context of climatic phenomena and disturbances.

Key Findings

• ATMOSPHERIC CO₂ AND SINK REDUCTION: Atmospheric CO₂ growth at Mauna Loa Observatory surged to 3.37 ± 0.11 ppm in 2023. This is twice the rate observed in the previous year, while fossil fuel emissions rose marginally by 0.6 ± 0.5%. This divergence indicates a notable decline in the global carbon sink's efficiency.
• LAND CARBON SINK DECLINE: The paper reports the weakest global net land CO₂ sink in two decades at 0.44 ± 0.21 GtC yr⁻¹, compared to an average of 2.04 GtC yr⁻¹ over the previous decade. This decline stands out starkly against historical records, emphasizing the negative impact of extreme climatic events and ecological disturbances.
• REGIONAL FLUX ANOMALIES: The paper documents significant carbon losses in the Amazon, Canada, and South-East Asia. During 2023, conditions such as drought, extreme fire emissions in Canada, and El Niño-like effects resulted in atypical carbon dynamics. Particularly, record fires in Canada led to emissions of 0.58 ± 0.10 GtC yr⁻¹, further exacerbating the reduction in carbon sequestration capacity.
• OCEAN CARBON SINK: Conversely, the ocean carbon sink demonstrated resilience, increasing by 0.10 GtC yr⁻¹ from 2022. The authors attribute this strengthening to diminished upwelling in the equatorial eastern Pacific, correlating with the transition from La Niña to moderate El Niño conditions.

Implications and Future Considerations

This paper elucidates the interconnectedness of climate events and carbon cycle dynamics, highlighting how extreme weather conditions, droughts, and fires significantly impinge upon terrestrial carbon uptake. The analysis poses critical questions for future Earth System models regarding their ability to anticipate rapid carbon losses through climate-induced disturbances and shifts in natural carbon sinks.

The findings underscore a concerning susceptibility of the terrestrial carbon sink to climatic variability, suggesting a potential shift in the capacity of these sinks to buffer anthropogenic CO₂ emissions effectively. This poses implications for carbon budget considerations and climate policy frameworks, particularly around net-zero targets.

From a practical standpoint, enhancing the resilience of natural carbon sinks will be crucial. This may necessitate adaptive management strategies for some of the most vulnerable ecosystems, including the boreal and tropical forests, to sustain carbon sequestration services amid increasing climatic extremes.

In conclusion, the research offers pivotal insights into the changing landscape of the global carbon budget, emphasizing the urgent need for robust strategies to mitigate further degradation of natural carbon sinks. As climate change progresses, such studies will become increasingly vital in guiding both scientific understandings and policy decisions on a global scale.