Hysteresis response of Northern Hemisphere winter temperature variability under different CO₂ removal pathways

Arctic amplification weakens the meridional temperature gradient (∂T/∂y), reducing the Northern Hemisphere winter daily temperature variability (Tstd). However, the extent to which Tstd recovers following CO₂ removal remains uncertain. We investigate the hysteresis and reversibility of Tstd under various CO₂ pathways using UKESM1-0-LL. The mid-latitude Tstd reduced during the ramp-up phase partially recovers following CO₂ removal, but its magnitude depends on the region and peak CO₂ concentration. In the low-concentration experiments, Tstd nearly returns to pre-industrial levels, whereas the high-concentration experiments show hysteresis and irreversibility in eastern Canada and northwestern Eurasia. These regional differences are primarily driven by changes in local temperature gradients. Specifically, the dominant factor for eastern Canada is the meridional temperature gradient, whereas for northwestern Eurasia, it is the zonal temperature gradient related to the land-sea thermal contrast. These results suggest that the response of Tstd to CO2 removal differs depending on the region and the peak concentration.