Changement climatique et Arctique et circulation océanique globale

Anthropogenic climate change is affecting major components of the Earth's climate system. Its impacts are pronounced at high latitudes, where the decline of Arctic sea ice is evident. Likewise, they are also clear in low latitudes, as exemplified by the enhanced warming of the tropical Indian Ocean. Accordingly, the overarching goal of this project is to investigate climatic links between the key element of global ocean circulation, the Atlantic meridional overturning circulation (AMOC), and changes in other ocean basins in the context of global warming. The project is led by Drs. Alexey Fedorov, Eric Guilyardi, and Juliette Mignot of the Laboratoire D'Oceanographie Et Du Climat Experimentations Et Approaches Numériques (LOCEAN). In 2023 the project also involved a postdoctoral associate Dr. Brady Ferster, a PhD student Yoania Povea-Perez, collaborators Drs. Leonard Borchert and Matthew Menary, other collaborators at LOCEAN, and international collaborators in the US.

During the past year, we focused on several problems related to the ocean inter-basin connections, specifically on the impacts of Indian Ocean warming on the Pacific, North Atlantic and Arctic climates. In particular, we discovered that a large fraction of climate variability in the North Atlantic could be attributed to the observed multi-decadal variations in TIO temperature over the past century or so (manuscript published in npj Journal of Climate and Atmospheric Sciences ). In addition, we conducted research on the broad problems of climate change and oceanic and atmospheric circulations. In total, in 2023 the ARCHANGE project supported 10 publications.

As part of her PhD work, Yoania Povea-Perez published the manuscript titled “The central role of the Atlantic southern overturning circulation in the Bjerknes compensation in a climate model” to Climate Dynamics . The Bjerknes compensation is a fundamental mechanism regulating global climate, such that changes in oceanic poleward heat transport can be compensated by changes in atmospheric heat transport. Poleward heat (energy) transport plays a major role in shaping the Earth's climate. Its oceanic and atmospheric components carry heat from low to high latitudes thus reducing the equator-to-pole temperature contrast. In quasi-equilibrium climate states, changes in the top-of-the-atmosphere (TOA) energy fluxes and ocean heat content remain small. In such conditions, anomalies in oceanic and atmospheric heat transport must have the same magnitude but opposite signs. This phenomenon is known as the Bjerknes compensation (BJC). However, to which extent BJC operates in the climate system and the key mechanisms of the compensation remain poorly understood. In this study, we have analyzed BJC in the IPSL-CM6A-LR climate model, focusing on its timescale dependence, its links to the Atlantic Meridional Overturning Circulation (AMOC), the connection to Intertropical Convergence Zone (ITCZ) shifts, and the processes affecting the marginal ice zone in the Arctic. Following this work, Yoania successfully defended her PhD thesis and graduated in July of 2023.

Finally, Dr. Eric Guilyardi and other lead investigators have conducted a broad range of extensive outreach and educational activities to educate the public on the physics and impacts of climate change.