Fig. 2: Spatial distribution of NH-winter blocking frequency and duration response during CO₂ pathway.

Ensemble-mean Northern Hemisphere winter blocking frequency differences between a CO₂ peak (2121–2160) and early ramp-up (2001–2040), b late ramp-down (2241–2280) and CO₂ peak, and c late ramp-down and early ramp-up periods. Blocking frequency is expressed in the percentage of winter days. Statistically significant differences at the 95% confidence level (two-tailed t-test) are dotted. Contours indicate the wintertime climatology of blocking frequency in control simulation (contour interval of 2%); d–f Number of blocking events as a function of duration in d Northern Hemisphere, e North Atlantic, and f North Pacific for the early ramp-up (red), CO₂ peak (black), and late ramp-down (blue) periods. The bottom plots show the difference between the late ramp-down and the early ramp-up period for each blocking duration, with filled bars denoting statistical significance at a 95% confidence level (two-tailed t-test).