Fig. 1: The occurrence of summer NAO extremes at 500 hPa increases under global warming.
From: More extreme summertime North Atlantic Oscillation under climate change
a Spatial patterns of the summer NAO in the first 10 years (1850–1859, shading) and the last 10 years (2090–2099, contour) of the Max Planck Institute Grand Ensemble (MPI_GE) historical and RCP8.5 runs. The percentages in the top parentheses indicate changes in the explained variance. b The distribution of the NAO index widens under the simulated global warming in the MPI_GE. Numbers in the top parentheses indicate changes in the standard deviation, with an asterisk indicating significance at the 5% confidence level based on bootstrapping. c Evolution of the occurrence of the positive NAO extremes every non-overlapping 10 years in the MPI_GE and MPI_GE_onepct. MPI_GE_onepct runs for 100 years with the initial condition of 1850, and forced by 1% CO2 increase per-year. Shading represents the 5–95% confidence interval based on bootstrapping. Numbers in the legend show the ensemble size. d Same as (c) but for negative NAO extremes. e Spatial pattern of the NAO in the NOAA-CIRES-DOE 20th century reanalysis (20CR) data during (1850–2015). The percentage in the top parentheses indicates the explained variance. f Distribution of the NAO index in the 20CR. The first 40 years represent (1850–1889) and the last 40 years represent (1976–2015). Numbers in the top parentheses indicate changes in the standard deviation, with an asterisk indicating significance at the 5% confidence level. g The occurrence of positive NAO extremes in the 20CR. 20CR_ens represents the 20CR with all the ensemble members. Error bars represent the 5–95% confidence interval based on bootstrapping. h Same as (g), but for negative NAO extremes.
