I see Martin Wild is still writing papers proving that Surface Solar Radiation (I tend to call it Bright Sunshine) is higher than in the past. (Thanks HockeySchtick)
All-sky SSR has been fairly stable with little variations in the first half of the 20th century, unlike the second half of the 20th century that is characterized also in Switzerland by a dimming from the 1950s to the 1980s and a subsequent brightening.
Does this graph of Sunshine changes look like the temperature changes graphs?
The effect of CO2 doubling is supposed to be 3.7W/m^2. In this table, changes in sunshine from 1981 to 2011 produce 5.59W/m^2 in December to 15.25W/m^2 in April.