Deciphering the Link Between Modeling Errors and the North Atlantic Surface Warming Pattern Projected by CMIP5 and CMIP6 Models

Abstract

The North Atlantic Subpolar Gyre (NASG) has warmed much less than the global ocean over recent decades, thereby suggesting a human‐caused slowdown of the Atlantic Meridional Overturning Circulation (AMOC). This North Atlantic “warming hole” is also found in climate projections, yet with a model‐dependent timing, location and intensity. Here we use two generations of global climate models and a Maximum Covariance analysis (MCA) to understand the reasons for this large inter‐model spread. Results suggest a key role of the present‐day Inter‐Tropical Convergence Zone (ITCZ) in conditioning the NASG surface warming projected at the end of the twenty‐first century. An original mechanism is proposed that relates the ITCZ mean state to the AMOC response via freshwater fluxes but also a balance between oceanic and atmospheric meridional heat transport. Finally, a related metric allows us to narrow the inter‐model spread in the NASG surface warming more effectively than the observed global warming.