Asymmetric response of day-to-day temperature variability to CO₂ forcing over Northern Hemisphere mid–high latitudes

Day-to-day temperature variability (DTDT) quantifies short-term temperature fluctuations and indicates weather-scale variability. Using idealized carbon dioxide removal (CDR) experiments, we assess the response asymmetry of DTDT over Northern Hemisphere mid-to-high latitudes under symmetric CO₂ ramp-up (RU) and ramp-down (RD) pathways. DTDT decreases with increasing CO₂ and remains strongly suppressed for about two decades after the CO₂ peak. Comparing CO₂ RU and RD periods with identical CO₂ concentrations, DTDT is systematically weaker during RD than during RU, indicating a pronounced response asymmetry to CO₂ forcing. This asymmetry is strongest in boreal winter and weaker in boreal summer. Using a decomposition of the thermodynamic energy equation, we find that the response asymmetry is primarily associated with weakened near-surface horizontal temperature advection, with additional contribution from changes in the variability of net surface radiative forcing. These results highlight the necessity of considering asymmetric and delayed recovery of short-term temperature variability in climate mitigation.