Yet another paper has appeared which documents the difficulty in skillfully predicting changes in regional and local climate statistics. This new paper is
Kim, Jinwon, Yu Gu, Kuo-Nan Liou, Rokjin J. Park and Chang-Keun Song, 2012: Direct and semi-direct radiative effects of anthropogenic aerosols in the Western United States: Seasonal and geographical variations according to regional climate characteristics. Climatic Change. Volume 111, Numbers 3-4, 859-877, DOI: 10.1007/s10584-011-0169-7
The abstract reads [highlight added]
“The direct and semi-direct radiative effects of anthropogenic aerosols on the radiative transfer and cloud fields in the Western United States (WUS) according to seasonal aerosol optical depth (AOD) and regional climate are examined using a regional climate model (RCM) in conjunction with the aerosol fields from a GEOS-Chem chemical-transport model (CTM) simulation. The two radiative effects cannot be separated within the experimental design in this study, thus the combined direct- and semi-direct effects are called radiative effects hereafter. The CTM shows that the AOD associated with the anthropogenic aerosols is chiefly due to sulfates with minor contributions from black carbon (BC) and that the AOD of the anthropogenic aerosol varies according to local emissions and the seasonal low-level winds. The RCM-simulated anthropogenic aerosol radiative effects vary according to the characteristics of regional climate, in addition to the AOD. The effects on the top of the atmosphere (TOA) outgoing shortwave radiation (OSRT) range from −0.2 Wm−2 to −1 Wm−2. In Northwestern US (NWUS), the maximum and minimum impact of anthropogenic aerosols on OSRT occurs in summer and winter, respectively, following the seasonal AOD. In Arizona-New Mexico (AZNM), the effect of anthropogenic sulfates on OSRT shows a bimodal distribution with winter/summer minima and spring/fall maxima, while the effect of anthropogenic BC shows a single peak in summer. The anthropogenic aerosols affect surface insolation range from −0.6 Wm−2 to −2.4 Wm−2, with similar variations found for the effects on OSRT except that the radiative effects of anthropogenic BC over AZNM show a bimodal distribution with spring/fall maxima and summer/winter minima. The radiative effects of anthropogenic sulfates on TOA outgoing longwave radiation (OLR) and the surface downward longwave radiation (DLRS) are notable only in summer and are characterized by strong geographical contrasts; the summer OLR in NWUS (AZNM) is reduced (enhanced) by 0.52 Wm−2 (1.14 Wm−2). The anthropogenic sulfates enhance (reduce) summer DLRS by 0.2 Wm−2 (0.65 Wm−2) in NWUS (AZNM). The anthropogenic BC affect DLRS noticeably only in AZNM during summer. The anthropogenic aerosols affect the cloud water path (CWP) and the radiative transfer noticeably only in summer when convective clouds are dominant. Primarily shortwave-reflecting anthropogenic sulfates decrease and increase CWP in AZNM and NWUS, respectively, however, the shortwave-absorbing anthropogenic BC reduces CWP in both regions. Due to strong feedback via convective clouds, the radiative effects of anthropogenic aerosols on the summer radiation field are more closely correlated with the changes in CWP than the AOD. The radiative effect of the total anthropogenic aerosols is dominated by the anthropogenic sulfates that contribute more than 80% of the total AOD associated with the anthropogenic aerosols.”
The bottom line from this study is that the aerosol effect is spatially and temporally quite complex. Without accurate information on the input of these aerosols and gases precursors into the atmosphere, the result will be that the models cannot achieve skillful predictions of changes in climate statistics. These aerosols also have non-radiative effects; e.g. see the Information Statement from the American Meteorological Society
which reads in part
“Aerosols act mostly as cloud-drop condensation nuclei (CCN), and some of them as ice nuclei (IN), both of which change …. precipitation properties in complex ways……… Aerosols….suppress precipitation from shallow or short-lived clouds (e.g., orographic cap clouds). Their impacts on deep convective clouds are much less certain, but are of potentially great importance. Recent research suggests that, depending on meteorological conditions, aerosols can either increase or decrease rainfall from such clouds. In warm moist atmospheres, aerosols often invigorate deep convective clouds, usually resulting in greater electrical activity, stronger damaging winds, and a greater likelihood of flash floods. Studies indicate that aerosols might also modulate the intensity of tornadoes and hurricanes.”
These aerosol effects make the challenge of accurately predicting changes in climate even more difficult just from the direct and semi-direct aerosol effects identified in the Kim et al 2012 paper .