Physical inconsistencies in the representation of the ocean heat-carbon nexus in simple climate models
Incohérences physiques dans la représentation du lien entre la chaleur de l'océan et le carbone dans les modèles climatiques simples
Séférian, Roland ; Bossy, Thomas ; Gasser, Thomas ; Nichols, Zebedee ; Dorheim, Kalyn ; Su, Xuanming ; Tsutsui, Junichi ; Santana-Falcón, Yeray
The Ocean Heat-Carbon Nexus, linking ocean heat and carbon uptake, is crucial for understanding climate responses to cumulative carbon dioxide (CO2) emissions and to net zero CO2 emissions. It results from a suite of processes involving the exchange of heat and carbon across the sea-air interface as well as their storage below the mixed layer and redistribution by the ocean large-scale circulation. The Ocean Heat and Carbon Nexus is assumed to be consistently represented across two modelling platforms used in the latest IPCC assessments: the Earth System Models (ESMs) and the Simple Climate Models (SCMs). However, our research shows significant deficiencies in state-of-the-art SCMs in replicating the ocean heat-carbon nexus of ESMs due to a crude treatment of the ocean thermal and carbon cycle coupling. With one SCM, we show that a more realistic heat-to-carbon uptake ratio exacerbates the projected warming by 0.1??°C in low overshoot scenarios and up to 0.2??°C in high overshoot scenarios. It is therefore critical to explore how SCMs' physical inconsistencies, such as the representation of the ocean heat-carbon nexus, can affect future warming projections used in climate assessments, not just by SCMs in Working Group 3 but also by ESMs in Working Group 1 via SCM-driven emission-to-concentration translation.</p>
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