Solar radiation is the dominant energy to drive the glacier melting over the Tibetan Plateau (TP). Because of low water vapor content, air mass, and aerosol concentration, the TP surface receives stronger solar radiation than its surroundings. However, the solar radiation over the TP experienced a transition from brightening to dimming around the end of the 1970s [Tang et al., 2011], which is different from the widely reported transition from dimming to brightening around 1990 in China [Che et al., 2005] and in the world [e.g., Stanhill and Cohen, 2001; Liepert, 2002; Pinker et al., 2005]. Aerosol optical depth (AOD) change has been suggested to play a role in the radiation change over China [e.g., Kaiser and Qian, 2002; Wang et al., 2012], India [e.g., Ramanathan and Ramana, 2005; Soni et al., 2012], Europe [e.g., Norris and Wild, 2007], and other regions [e.g. Ohmura, 2009; Wild, 2012]. However, the situation over the TP is somehow unique. On one hand, this region is one of the cleanest regions in the world. A recent measured baseline AOD at 500 nm is only 0.029 at an AERONET station in central TP. Thus, Tang et al.  speculated that the solar dimming over the TP may be caused by cloud change. On the other hand, total cloud cover (TCC) at China Meteorological Administration (CMA) stations shows an overall decreasing trend [Xia, 2010], whereas recent studies [Xu et al., 2009; Lu et al., 2012] suggested an increase in black carbon (BC) on the TP. The TOMS (Total Ozone Mapping Spectrometer) aerosol index also shows a slightly increasing trend since 1978 over the Plateau [Yi and Zhou, 2011]. Therefore, it is likely that the increase in aerosols may explain the paradox between the dimming and TCC decreasing. Indeed, You et al.  suggested “transient aerosol emissions as a plausible cause” for the solar dimming. Nevertheless, a physical quantification was not given by either Tang et al.  or You et al. .
 As aerosol change over the TP and its surroundings has become a focus in terms of its hydrological effects [Xu et al., 2009; Qian et al., 2011], it is critical to clarify the role of aerosol loading in the dimming. In this study, we show that the solar dimming is mainly caused by the increase in water vapor amount and deep cloud cover but not aerosol loading.