Global warming may not be the only factor responsible for glacial retreat. Huss et al. (2009) investigated the effect of solar radiation on glacier melting at four high elevation sites in the European Alps. They found that snow and ice melt was stronger in the 1940s than in recent years in spite of significantly higher air temperatures in the present decade. An inner Alpine radiation record “shows that in the 1940s global shortwave radiation over the summer months was 8% above the long-term average and significantly higher than today, favoring rapid glacier mass loss.” Dimming of solar radiation from the 1950s until the 1980s is in line with reduced melt rates and advancing glaciers, suggesting that solar radiation plays a major factor in glacier retreat. — Grace Beck
Huss, M., Funk, M., Ohmura, A. 2009. Strong Alpine glacier melt in the 1940s due to enhanced solar radiation. Geophysical Research Letters. 36, L23501
After reviewing 94 years of seasonal mass balance data collected at four different Swiss glaciers, Huss et al. concluded that melting conditions have undergone strong temporal variations throughout the last century. During 1942–1952 and 1998–2008 melting was above average (17% and 13% respectively) while it was below average from 1971–1981 (–19%). According to the century-long data series, maximum melting at the study sites occurred in 1947. In fact, melting rates were observed to be substantially higher in 1947 than those in the summer of 2003, which is known for its extreme heat waves in Europe. This phenomenon is intriguing because air temperatures in the 1940s were not as high as they were in 2003.
As a result of their findings, Huss et al. deduced that solar radiation must be a key factor in glacier melting patterns. According to global radiation records collected during the 20th century, maximum global radiation was recorded in the 1940s. During this period, summer radiation was 8% above the long-term average and 18 Wm-2 higher than over the last decade. Huss et al.’s findings suggest that extreme glacier melt rates in the 1940s were mostly due to radiation changes rather than to climate change.