Low latency global carbon budget reveals a continuous decline of the land carbon sink during the 2023/24 El Nino event (2504.09189v1)

Abstract: The high growth rate of atmospheric CO2 in 2023 was found to be caused by a severe reduction of the global net land carbon sink. Here we update the global CO2 budget from January 1st to July 1st 2024, during which El Ni~no drought conditions continued to prevail in the Tropics but ceased by March 2024. We used three dynamic global vegetation models (DGVMs), machine learning emulators of ocean models, three atmospheric inversions driven by observations from the second Orbiting Carbon Observatory (OCO-2) satellite, and near-real-time fossil CO2 emissions estimates. In a one-year period from July 2023 to July 2024 covering the El Ni~no 2023/24 event, we found a record-high CO2 growth rate of 3.66~$\pm$~0.09 ppm~yr$^{-1}$ ($\pm$~1 standard deviation) since 1979. Yet, the CO2 growth rate anomaly obtained after removing the long term trend is 1.1 ppm~yr$^{-1}$, which is marginally smaller than the July--July growth rate anomalies of the two major previous El Ni~no events in 1997/98 and 2015/16. The atmospheric CO2 growth rate anomaly was primarily driven by a 2.24 GtC~yr$^{-1}$ reduction in the net land sink including 0.3 GtC~yr$^{-1}$ of fire emissions, partly offset by a 0.38 GtC~yr$^{-1}$ increase in the ocean sink relative to the 2015--2022 July--July mean. The tropics accounted for 97.5\% of the land CO2 flux anomaly, led by the Amazon (50.6\%), central Africa (34\%), and Southeast Asia (8.2\%), with extra-tropical sources in South Africa and southern Brazil during April--July 2024. Our three DGVMs suggest greater tropical CO2 losses in 2023/2024 than during the two previous large El Ni~no in 1997/98 and 2015/16, whereas inversions indicate losses more comparable to 2015/16. Overall, this update of the low latency budget highlights the impact of recent El Ni~no droughts in explaining the high CO2 growth rate until July 2024.

Analysis of the Decline in Land Carbon Sink During the 2023/24 El Niño Event

The paper "Low latency global carbon budget reveals a continuous decline of the land carbon sink during the 2023/24. El Niño event" presents a thorough examination of the global carbon budget from July 2023 to July 2024, focusing specifically on the effects of the 2023/24 El Niño. The paper utilizes a combination of dynamic global vegetation models (DGVMs), machine learning emulators of ocean models, atmospheric inversions, and fossil CO2 emissions estimates to provide insights into the global carbon budget dynamics during this period.

Key Findings

The research identifies a record-high atmospheric CO2 growth rate of 3.66 ± 0.09 ppm yr-1, attributed primarily to a significant reduction in the global land carbon sink, particularly due to drought conditions in the tropics. Notably, the net land carbon sink declined by 2.24 GtC yr-1, including 0.3 GtC yr-1 from fire emissions. Although there was a 0.38 GtC yr-1 increase in the ocean sink, it was insufficient to offset the decrease in the land sink, leading to a considerable CO2 growth anomaly.

Regional analysis indicates that the tropics accounted for 97.5% of the land CO2 flux anomaly, with the Amazon alone contributing 50.6%. The DGVMs suggest greater tropical CO2 losses in 2023/24 than during previous El Niño events in 1997/98 and 2015/16, although atmospheric inversions paint a less severe picture, comparable with the 2015/16 event. This divergence highlights discrepancies in quantifying terrestrial responses to climatic events, underscoring the importance of model validation and refinement.

Implications

The continued increase in atmospheric CO2 has profound implications for global climate change, necessitating precise and actionable intelligence on carbon sinks and sources. Understanding the dynamics of the carbon budget in relation to climatic events such as El Niño provides essential knowledge for predicting future CO2 trends and for formulating mitigation strategies.

This paper emphasizes the vulnerabilities of the global land carbon sink to climatic anomalies, which may exacerbate anthropogenic climate change effects. It proposes further investigation into the interactions between climatic events and biospheric feedback mechanisms, particularly the response of vegetation models to drought-induced stress and mortality.

Methodological Insights

By integrating top-down and bottom-up approaches, the paper leverages observational data with model-driven predictions, achieving a comprehensive view of the carbon budget. The use of machine learning emulators to estimate ocean and land carbon fluxes represents a sophisticated approach in modeling complex ecological processes. These innovations underscore the potential of artificial intelligence in enhancing climate modeling and forecasting.

Looking Forward

While the paper provides crucial data on the 2023/24 El Niño event, ongoing research is necessary to improve model accuracy and integrate additional environmental factors. Future studies may expand the use of ML emulators to encapsulate broader ecological variables, enhancing predictive capabilities.

In conclusion, the research delivers a meticulous account of the carbon budget dynamics during the 2023/24 El Niño, revealing critical trends and regional contributions to the global carbon flux. Its findings are vital for understanding and addressing the challenges posed by climatic and anthropogenic factors on the global carbon cycle, aiding in the design of more effective climate action policies.