A poster presentation from Institute for Atmospheric and Climate Science - ETH Zurich finds that "Diurnal temperature range, solar radiation and sunshine duration are closely correlated on decadal timescales." The authors also conclude, "solar radiation has experienced not only a brightening towards the end of the 20th century, but also an earlier period of brightening in the first half of the last century."
Figure 2 from the poster shows a dimming of solar radiation at the surface of the Earth during the 70's ice age scare from 1970 to ~1987, and a subsequent brightening of solar radiation by almost 5 W/m2 from ~1987 to the end of the record in 2005. The data shows the change in solar radiation corresponds to an increase in diurnal temperature range anomalies by almost 0.5C.
By way of comparison, the IPCC alleges that a doubling of CO2 levels would increase forcing at the top of the atmosphere by 3.7 W/m2 and at the Earth surface by only about 1 W/m2. Using the actual change in CO2 levels between 1987 and 2005, the IPCC formula alleges forcing from CO2 increased only 0.45 W/m2 at the top of the atmosphere [5.35*ln(379.80/349.16)] and a mere 0.12 W/m2 [1/3.7*0.45] at the Earth surface from 1987 to 2005.
The data also show an excellent correlation between solar radiation at the surface and diurnal temperature range (R² of = 0.87), which far exceeds the correlation between CO2 and temperature (R² = 0.44). Thus, changes in solar radiation at the Earth surface dominate climate change, not greenhouse gases.
Knut Makowski, Marc Chiacchio, Arturo Sanchez-Lorenzo & Martin Wild
The diurnal temperature range (DTR), which is defined as the difference between daily maximum and minimum temperature is considered a useful measure to investigate the development of local and regional changes in the energy balance because it is strongly influenced by its most important element - the incoming solar radiation (Makowski et al. 2008). The recently identified increase of DTR over Western Europe since 1985, is subsequent to the well known decrease since 1950, both are in line with the Global Dimming and Brightening phenomenon. Consequently, we extended our investigations on DTR back to the first half of the 20th century. In a previous study we focused on the influence of solar radiation on DTR, this time we aim at learning more on the evolution of solar radiation using our DTR series as proxies.