AR4 draws no conclusion on global changes in snowfall. Changes in snowfall are discussed on a region-by-region basis, but focussed mainly on North America and Eurasia. Statistically significant increases were found in most of Canada, parts of northern Europe and Russia. A number of areas showed a decline in the number of snowfall events, especially those where climatological averaged temperatures were close to 0°C and where warming led to earlier onset of spring. Also, an increase in lake-effect snowfall was found for areas near the North American Great Lakes.
Since AR4, most published literature has considered again changes in snowfall in North America. These studies have confirmed that more winter-time precipitation is falling as rain rather than snow in the western USA (Knowles et al., 2006), the Pacific Northwest and Central USA (Feng and Hu, 2007). Kunkel et al. (2009) analyzed trends using a specially quality-controlled data set of snowfall observations over the contiguous USA and found that snowfall has been declining in the western USA, northeastern USA and southern margins of the seasonal snow region, but increasing in the western Great Plains and Great Lakes regions. Snowfall in Canada has increased mainly in the north while a significant decrease was observed in the southwestern part of the country for 1950–2009 (Mekis and Vincent, 2011).
Other regions that have been analyzed include Japan (Takeuchi et al., 2008), where warmer winters in the heavy snowfall areas on Honshu are associated with decreases in snowfall and precipitation in general. Shekar et al. (2010) found declines in total seasonal snowfall along with increases in maximum and minimum temperatures in the western Himalaya. Serquet et al. (2011) analyzed snowfall and rainfall days since 1961 and found the proportion of snowfall days to rainfall days in Switzerland was declining in association with increasing temperatures. Scherrer and Appenzeller (2006) found a trend in a pattern of variability of snowfall in the Swiss Alps that indicated decreasing snow at low altitudes relative to high altitudes, but with large decadal variability in key snow indicators (Scherrer et al., 2013). Van Ommen and Morgan (2010) draw a link between increased snowfall in coastal East Antarctica and increased southwest Western Australia drought. However, Monaghan and Bromwich (2008) found an increase in snow accumulation over all Antarctica from the late 1950s to 1990, then a decline to 2004. Thus snowfall changes in Antarctica remain uncertain.
In summary, in most regions analyzed, it is likely that decreasing numbers of snowfall events are occurring where increased winter temperatures have been observed (North America, Europe, Southern and East Asia). Confidence is low for the changes in snowfall over Antarctica.