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The United States “warming hole”: Quantifying the forced aerosol response given large internal variability
Author(s) -
Banerjee A.,
Polvani L. M.,
Fyfe J. C.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl071567
Subject(s) - aerosol , environmental science , forcing (mathematics) , climatology , atmospheric sciences , climate model , radiative forcing , climate change , meteorology , oceanography , geology , geography
Twenty‐five years of large summer cooling over the southeastern United States ending in the mid‐1970s coincided with rapidly increasing anthropogenic aerosol emissions. Here we assess the claim that the cooling in that period was predominantly due to such aerosols. We utilize two 50‐member sets of coupled climate model simulations, one with only anthropogenic aerosol forcings and another with all known natural and anthropogenic forcings, together with a long control integration. We show that, in the absence of aerosol forcing, none of the model simulations capture the observed surface cooling rate (∼0.56°C decade −1 ), whereas with increasing aerosol emissions 2 (of 50) of the simulations do. More importantly, however, we find that the cooling from aerosols (0.20°C decade −1 ) is insufficient to explain the observation. Our results therefore suggest that, while aerosols may have played a role, the observed cooling was a rare event that contained a large contribution from unforced internal variability.