Abstract

Observations show that the surface incident solar radiation (R_s) decreased over land from the 1950s to the 1980s and increased thereafter, known as global dimming and brightening. This claim has been questioned due to the inhomogeneity and low spatial-temporal coverage of R_s observations. Based on direct comparisons of 200 observed and sunshine duration (SunDu) derived R_s station pairs, meeting data record lengths exceeding 60 months and spatial distances less than 110 km, we show that meteorological observations of SunDu can be used as a proxy for measured R_s. Our revised results from 2,600 stations show global dimming from the 1950s to the 1980s over China (-1.90 W/m² per decade), Europe (-1.36 W/m² per decade), and the United States (-1.10 W/m² per decade), brightening from 1980 to 2009 in Europe (1.66 W/m² per decade) and a decline from 1994 to 2010 in China (-1.06 W/m² per decade). Even if 1994-2010 is well known as a period of global brightening, the observed and SunDu-derived R_s over China still exhibit declining trends. Trends in R_s from 1923 to 1950 are also found over Europe (1.91 W/m² per decade) and the United States (-1.31 W/m² per decade), but the results in Europe may not well represent the actual trend for the European continent due to poor spatial sampling.