How do aerosol histories affect solar “dimming” and “brightening” over Europe?: IPCC‐AR4 models versus observations

Abstract

A multidecadal decrease in downward surface solar radiation (solar “dimming”) followed by a multidecadal increase in surface radiation (solar “brightening”) have been reported over Europe. The trends mainly occur under cloud‐free skies, and they are primarily caused by the direct aerosol radiative effect. The present study compares observed cloud‐free solar “dimming” and “brightening” trends with corresponding output from IPCC‐AR4 20th century simulations and furthermore examines how sulfate and black carbon aerosol histories, used as model input, affect simulated surface radiation trends. Outputs from 14 models are compared to observed cloud‐free surface radiation fluxes derived from a combination of (1) satellite cloud observations, synoptic cloud reports, and surface solar irradiance measurements and (2) sunshine duration measurements and variability of the atmospheric transmittance derived from solar irradiance measurements. Most models display a transition from decreasing to increasing solar irradiance, but the timing of the reversal varies by about 25 years. Consequently, large discrepancies in sign and magnitude occur between modeled and observed “dimming” and “brightening” trends (up to 4.5 Wm−2 per decade for Europe). Considering all models with identical aerosol histories, differences in cloud‐free radiation trends are in all but one case less than 0.7 Wm−2 per decade. Thirteen of the fourteen models produce a transition from “dimming” to “brightening” that is consistent with the timing of the reversal from increasing to decreasing aerosol emissions in the input aerosol history. Consequently, the poor agreement between modeled and observed “dimming” and “brightening” is due to incorrect aerosol emission histories rather than other factors.

The Global Energy Balance Archive (GEBA) version 2017: a database for worldwide measured surface energy fluxes

“…These studies show that climate models typically do not fully reproduce the strong multidecadal variations seen in the GEBA data (Ruckstuhl and Norris, 2009;Wild and Schmucki, 2011;Zubler et al, 2011;Allen et al, 2013;Bartok et al, 2017). The inadequate representation of decadal changes in aerosols has been suggested as a potential cause for the lack of trends in the simulated surface downward shortwave radiation fields.…”

Detection and attribution of anthropogenic forcing to diurnal temperature range changes from 1950 to 1999: comparing multi-model simulations with observations

“…Very likely, the small DTR trend in ALL may result mainly from the underestimated T min trend due to the lack of increased cloudiness, which acts as a blanket at night to warm the surface (i.e., the increase of DLW). In addition, the models are limited in describing realistic effects of aerosols (including their properties) and cloudaerosol interactions and thus in simulating changes in surface radiation (Ruckstuhl and Norris 2009;Wild 2009). For example, the observed large decreases in DTR over eastern China, where cloudiness decreased and aerosols increased substantially (Kaiser 1998;Liu et al 2004;Zhou et al 2008), and the observed solar ''dimming'' and ''brightening'' over Europe (Ruckstuhl and Norris 2009;Wild 2009), are not realistically simulated.…”

“…In addition, the models are limited in describing realistic effects of aerosols (including their properties) and cloudaerosol interactions and thus in simulating changes in surface radiation (Ruckstuhl and Norris 2009;Wild 2009). For example, the observed large decreases in DTR over eastern China, where cloudiness decreased and aerosols increased substantially (Kaiser 1998;Liu et al 2004;Zhou et al 2008), and the observed solar ''dimming'' and ''brightening'' over Europe (Ruckstuhl and Norris 2009;Wild 2009), are not realistically simulated. Considering large uncertainties in simulating changes in clouds, aerosols, and hydrological variables (e.g., precipitation, soil moisture) in the models, very likely the missing increasing trend in the simulated cloudiness is a major reason to explain the small DTR trend in the models.…”

Is global dimming and brightening in Japan limited to urban areas?

“…It is a subject of debate that the observed decadal SSR trends are generally stronger than those simulated by a number of models, although such trends in several different regions of the world are qualitatively well reproduced by some models (Ruckstuhl and Norris, 2009;Dwyer et al, 2010;Skeie et al, 2011;Wild and Schmucki, 2011;Allen et al, 2013). From both model and observational perspectives, hypotheses have been put forward to explain the discrepancy between the observed and simulated SSR trends as summarized below:…”

“…From the model perspective, four conceivable reasons are (a) the resolutions of the models used in these studies are too coarse to capture the effects of local air pollution on SSR (Skeie et al, 2011), (b) the models do not describe aerosol and cloud effects and their interactions sufficiently (Skeie et al, 2011;Allen et al, 2013), (c) historical aerosol emission inventories are incorrect (Ruckstuhl and Norris, 2009;Allen et al, 2013), and (d) inaccurate variations in the aerosol fields are used in the models (Wild and Schmucki, 2011).…”