It's not 'one thing', it's a series of measurements over time.
> "Since the late 1970's there has been a significant reduction in the average number of days with snow lying, based on a sample of climatological stations at altitudes between 100m and 400m. The average rate of change has been 12 days per decade, which has been associated with changes in mean temperature during the winter months. The average number of days with snow lying across Scotland as a whole during the winter (November to April) is reduced by 9 days for every 1.0oC increase in mean temperature."
That's from a paper published in 2000, which is useful to look at because it makes projections for avg time periods (30-yr means) centered on 2020, 2050, and 2080.
These projections from 2000 are kind of interesting. We don't seem to be in the absolute worst-case projection (current snow loss in the Alps appears to be 77%, not 100%, for example [1]):
> "Whetton et al. (1996) have used GCM’s to simulate changes in snow cover in the Australian Alps using a mass balance approach (snowfall less ablation). They conclude that in a worst-case scenario, all snow will have disappeared from the Alps by the 2020’s. Barringer (1996) translates snow cover into altitude of snowlines which, under a best case scenario, retreat upwards at the rate of 10m per decade, rising to 52m per decade in a worst case scenario. Hantel et al. (2000) translate incremental temperature changes into numbers of snow days which, at lower altitudes, would mean a reduction of 31 days in winter and 42 days in spring for a temperature increase of 1oC."
[0] CLIMATE CHANGE AND CHANGING PATTERNS OF SNOWFALL IN SCOTLAND
J Harrison, S Winterbottom - 2000
What (if anything) to do about this reality is a matter of debate, but there's no mistake that steady global warming is taking place, fairly in line with projections dating back several decades at least.
> "Since the late 1970's there has been a significant reduction in the average number of days with snow lying, based on a sample of climatological stations at altitudes between 100m and 400m. The average rate of change has been 12 days per decade, which has been associated with changes in mean temperature during the winter months. The average number of days with snow lying across Scotland as a whole during the winter (November to April) is reduced by 9 days for every 1.0oC increase in mean temperature."
That's from a paper published in 2000, which is useful to look at because it makes projections for avg time periods (30-yr means) centered on 2020, 2050, and 2080.
These projections from 2000 are kind of interesting. We don't seem to be in the absolute worst-case projection (current snow loss in the Alps appears to be 77%, not 100%, for example [1]):
> "Whetton et al. (1996) have used GCM’s to simulate changes in snow cover in the Australian Alps using a mass balance approach (snowfall less ablation). They conclude that in a worst-case scenario, all snow will have disappeared from the Alps by the 2020’s. Barringer (1996) translates snow cover into altitude of snowlines which, under a best case scenario, retreat upwards at the rate of 10m per decade, rising to 52m per decade in a worst case scenario. Hantel et al. (2000) translate incremental temperature changes into numbers of snow days which, at lower altitudes, would mean a reduction of 31 days in winter and 42 days in spring for a temperature increase of 1oC."
[0] CLIMATE CHANGE AND CHANGING PATTERNS OF SNOWFALL IN SCOTLAND J Harrison, S Winterbottom - 2000
[1] https://news.yahoo.com/alps-getting-greener-thats-not-184713...
What (if anything) to do about this reality is a matter of debate, but there's no mistake that steady global warming is taking place, fairly in line with projections dating back several decades at least.