Fig. 2: Relationship between GSAT and AMOC over the historical period.
From: Increased risk of near term global warming due to a recent AMOC weakening
a Scatter plot of Global near-Surface Air Temperature (GSAT) (K decade−1) versus Atlantic Meridional Overturning Circulation (AMOC) (Sv decade−1) trends calculated over the 1940-2016 period from the IPSL ensemble of extended historical simulations (IPSL-EHS; filled circles) and the observations (dot-dashed lines), with HadCRUT4-CW41,42 for the temperature and the Caesar index17 as a proxy for the AMOC evolution, with the related uncertainties (gray). The black solid line represents the least square regression between these two variables in IPSL-EHS, with a determination coefficient r² = 0.82 (p < 0.1, see Method). The color scale represents the RMSE between simulated and observed (HadCRUT4-CW41,42) annual GSAT anomalies over the period 1900–2018. b Time evolution of the low-pass filtered AMOC strength anomaly from IPSL-EHS (gray), the AMOC forced signal (or ensemble mean, red), and the subset of 6 members labelled in a (light blue), with the subset average (dark blue). The anomaly is calculated for each member with respect to its 1850–2018 average. A Lanczos low-pass filter with a cutoff period of 11 years is used.
