The reduction of global radiation in south-eastern Norway during the last 50 years

At the Norwegian University of Life Sciences ( previously known as the Agricultural University of Norway), measurements of global radiation have been performed since 1949. Rurally located, 35 km south of Oslo (59 degrees 40'N, 10 degrees 46'E), the local climate is not affected by industry or heavy traffic. The recent focus on global dimming in the scientific literature, and the impact a reduction of solar radiation on the Earth's surface would have on agriculture and the biosphere in general, motivated us to collect and analyze the global radiation data. On a monthly basis, the reduction in radiation varied between more than 4% per decade in April and June to less than 2% per decade in January and May. The analyses show a reduction in the annual sum of global radiation by 2.5% or 3.1% per decade, depending on whether analyses were restricted to years with reliable and complete data sets (31 years from 1950 to 2003) or included all individual months with reliable data (545 months) were used.