Physical inconsistencies in the representation of the ocean heat-carbon nexus in simple climate models

• Published in: Communications earth & environment 2024-06, Vol.5 (1), p.291-10, Article 291
• Main Authors: Séférian, Roland, Bossy, Thomas, Gasser, Thomas, Nichols, Zebedee, Dorheim, Kalyn, Su, Xuanming, Tsutsui, Junichi, Santana-Falcón, Yeray
• Format: Article
• Language: English
• Subjects: Assessments; Carbon cycle; Carbon dioxide; Carbon dioxide emissions; Climate models; Continental interfaces, environment; Emission; Emissions; Environmental assessment; ENVIRONMENTAL SCIENCES; Heat; Heat exchange; Intergovernmental Panel on Climate Change; Ocean models; Ocean, Atmosphere; Representations; Sciences of the Universe; Translation; Working groups
• ISSN: 2662-4435; 2662-4435
• DOI: 10.1038/s43247-024-01464-x

The Ocean Heat-Carbon Nexus, linking ocean heat and carbon uptake, is crucial for understanding climate responses to cumulative carbon dioxide (CO 2 ) emissions and to net zero CO 2 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.