Early or delayed Northern Hemisphere warming driven by the AMOC in a net-zero CO2 world

Abstract

Most countries have committed to achieving carbon neutrality by 2050 to limit global warming to 1.5 °C–2 °C above pre-industrial levels. However, the response of Northern Hemisphere (NH) surface temperatures respond under net-zero CO₂ remains uncertain. Using climate model simulations, we have found that NH temperatures exhibit either early or delayed warming following the achievement of net-zero emissions. These divergent responses are driven by differences in the Atlantic Meridional Overturning Circulation (AMOC), which begins to diverge ~50 years prior to net-zero. In cases of early warming, increased salinity in the subpolar Atlantic leads to earlier AMOC recovery. Conversely, delayed AMOC recovery postpones NH warming. These results highlight the critical role of pre-net-zero conditions in the subpolar North Atlantic in determining the divergent responses of NH warming after net-zero emissions.