During the satellite era (1979-present), the tropical Pacific Ocean has warmed significantly less than the other tropical oceans in response to increasing greenhouse gases (GHGs). This La Niña-like warming trend in observations is in disagreement with the El Niño-like warming trend projected by the Coupled Model Intercomparison Project (CMIP) models for both the 20th and 21st century. It remains unresolved whether the La Niña-like sea surface temperature (SST) trend pattern during the satellite era is driven by either external forcing or internal variability. A new study published in npj Climate and Atmospheric Science (Chung et al., 2024) conducted a comprehensive analysis of observations and a series of climate model simulations for the historical period to conclude that a combination of internal variability and human activity has shaped the observed La Niña-like SST trend pattern. The study further concluded that human-induced stratospheric ozone depletion has acted to enhance the La Niña-like SST trend pattern by strengthening the atmospheric meridional circulations and associated Pacific trade winds. These results suggest that the current La Niña-like SST trend will likely disappear in the near future due to the projected recovery of the stratospheric ozone layer.
Modified Figures 4d & 4h from Chung et al. (2024). (Upper panel) Mult-model, multi-ensemble mean SST trends (unit: K decade−1) in response to historical stratospheric ozone concentration changes over 1979–2010. (Lower Panel) Same as the upper panel but for trends in sea level pressure (shading, unit: Pa decade−1) and 850-hPa winds (vectors, unit: m s−1 decade−1).
Chung, ES., Kim, SJ., Lee, SK. et al. Tropical eastern Pacific cooling trend reinforced by human activity. npj Clim Atmos Sci 7, 170 (2024). https://doi.org/10.1038/s41612-024-00713-2
Ocean to Climate 