[A-CG31] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG31-02] Extending the Horizon of Climate Predictions and Projections through Earth System Insights on Carbon Cycle

★Invited Papers

*Hongmei Li^1,2、Tatiana Ilyina^3,1,2 (1.Helmholtz-Zentrum Hereon, Geesthacht, Germany、2.Max Planck Institute for Meteorology, Hamburg, Germany、3.Universität Hamburg, Hamburg, Germany)

キーワード：Global carbon cycle, Predictions, Reconstructions, Internal climate variability

The variable global carbon cycle, encompassing CO₂ fluxes among the atmosphere, ocean, and land reservoirs, plays a pivotal role in modulating climate variations. Concurrently, emissions intensity and natural climate variability influence fluctuations in the carbon cycle. Understanding these interactions over time is crucial for predicting and projecting climate changes, as well as evaluating the effectiveness of climate adaptation and mitigation strategies. Previous studies on seasonal to decadal predictions underline the advantages of predicting the evolution of the climate such as the temperature and circulations by initializing the climate models with observations. We extend the climate model predictions to the Earth System, incorporating the biogeochemical processes, and further develop a new framework of Earth system modeling forced by CO₂ emissions allowing prognostic atmospheric CO₂ with an interactive carbon cycle to reconstruct and predict the global carbon cycle.

Through assimilating physical atmospheric and oceanic data products, reconstructions can reproduce the historical variations of air-sea and air-land CO₂ fluxes and the corresponding atmospheric CO₂ growth in line with the available observations, providing an additional line for assessing the global carbon budget. Within a closed Earth system, these reconstructions offer a comprehensive perspective on the variations of the global carbon cycle in recent decades, addressing the challenge presented by the limited availability of carbon cycle measurements. Predictions initialized from the reconstructions demonstrate high confidence in predicting changes in the global carbon cycle for the next few years. The predictive skill extends up to 5 years for the air–sea CO₂ fluxes and 2 years for the air–land CO₂ fluxes and atmospheric carbon growth rate. In the meanwhile, we conducted large ensemble simulations to investigate the internal variability and future projections of the global carbon cycle and climate change in response to various emission pathways. The decadal variations of air-sea CO₂ fluxes can be partially attributed to internal climate variability. Despite mitigating CO2 emissions, the earth’s temperatures continue to rise afterward. We also observed that long-term changes in the carbon cycle exhibit asymmetry to CO₂ emissions across different scenario pathways.