Northern Hemisphere continental winter warming following the 1991 Mt. Pinatubo eruption: reconciling models and observations Journal Article uri icon



  • Abstract. It has been suggested, and is widely believed, that the anomalous surface warming observed over; the Northern Hemisphere continents in the winter following the 1991 eruption of Mt. Pinatubo was,; in fact, caused by that eruption, via a stratospheric pathway that involves a strengthening of the; polar vortex. However, most studies that have examined multiple, state-of-the-art, coupled; climate models report that, in the ensemble mean, the models do not show winter warming after the; Mt. Pinatubo eruption. This lack of surface warming in the multi-model mean, concomitant with a; frequent lack of strengthening of the polar vortex, is often interpreted as a failure of the; models to reproduce the observations. In this paper we show that this interpretation is; erroneous, as averaging many simulations from different models, or from the same model, is not; expected to yield surface anomalies similar to the observed ones, even if the models were highly; accurate, owing to the presence of strong internal variability. We here analyze three large ensembles of state-of-the-art, coupled climate model simulations and; show that, in all three, many individual ensemble members are able to produce post-Pinatubo; surface warming in winter that is comparable to the observed one. This establishes that; current-generation climate models are perfectly capable of reproducing the observed surface; post-eruption warming. We also confirm the bulk of previous studies, and show that the surface; anomaly is not statistically different from zero when averaged across ensembles of; simulations, which we interpret as the simple fact that the volcanic impact on continental winter; temperatures is tiny compared to internal variability. We also carefully examine the stratospheric pathway in our models and, again confirming previous; work, show that any strengthening of the polar vortex caused by the Mt. Pinatubo eruption is very; small (of the order of a few meters per second at best). Such minuscule anomalies of the stratospheric; circulation are completely overwhelmed by the tropospheric variability at midlatitudes, which is; known to be very large: this explains the lack of surface winter warming in the ensemble means. In summary, our analysis and interpretation offer compelling new evidence that the observed; warming of the Northern Hemisphere continents in the winter 1991–1992 was very likely unrelated to; the 1991 Mt. Pinatubo eruption.;

publication date

  • May 15, 2019

Date in CU Experts

  • June 11, 2021 3:22 AM

Full Author List

  • Polvani LM; Banerjee A; Schmidt A

author count

  • 3

Other Profiles

Electronic International Standard Serial Number (EISSN)

  • 1680-7324

Additional Document Info

start page

  • 6351

end page

  • 6366


  • 19


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