Future Changes to El Niño Teleconnections over the North Pacific and North America

• Published in: Journal of climate 2021-08, Vol.34 (15), p.6191-6205
• Main Authors: Beverley, Jonathan D., Collins, Matthew, Lambert, F. Hugo, Chadwick, Robin
• Format: Article
• Language: English
• Subjects: Anomalies; Barotropic mode; Carbon dioxide; Circulation anomalies; Climate variability; El Nino; El Nino events; El Nino phenomena; El Nino-Southern Oscillation event; Equator; Herbivores; Modelling; Planetary waves; Precipitation; Precipitation anomalies; Remote regions; Rossby waves; Southern Oscillation; Statistical analysis; Teleconnections; Temperature anomalies; Temperature gradients
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-20-0877.1

El Niño–Southern Oscillation (ENSO) is the leading mode of interannual climate variability, and it exerts a strong influence on many remote regions of the world, for example in northern North America. Here, we examine future changes to the positive-phase ENSO teleconnection to the North Pacific/North America sector and investigate the mechanisms involved. We find that the positive temperature anomalies over Alaska and northern North America that are associated with an El Niño event in the present day are much weaker, or of the opposite sign, in the CMIP6 abrupt 4×CO₂ experiments for almost all models (22 out of 26, of which 15 have statistically significant differences). This is largely related to changes to the anomalous circulation over the North Pacific, rather than differences in the equator-to-pole temperature gradient. Using a barotropic model, run with different background circulation basic states and Rossby wave source forcing patterns from the individual CMIP6 models, we find that changes to the forcing from the equatorial central Pacific precipitation anomalies are more important than changes in the global basic state background circulation. By further decomposing this forcing change into changes associated with the longitude and magnitude of ENSO precipitation anomalies, we demonstrate that the projected overall eastward shift of ENSO precipitation is the main driver of the temperature teleconnection change, rather than the increase in magnitude of El Niño precipitation anomalies, which is nevertheless seen in the majority of models.