Air temperature changes until now

Climate measurement series of ground-level temperatures in Switzerland date back to the mid-19th century. The mean annual temperature has increased by 1.6°C between 1864 and 2008 with respect to 1961-1990 average conditions. Over the past 100 years (1909-2008), mean annual temperatures increased by 0.12-0.19°C per decade, with no distinctive regional differences. Temperature increase has accelerated substantially in recent decades (1). An increase of more than 1°C in average temperature has been observed in Austria during the last century (25). For Austria, a widespread warming trend in both daily minimum and maximum temperatures was confirmed for homogenized time series of temperature data covering the period 1948–2009 (31).

Recent research suggests that there is a similar air temperature trend in the Alps at low and very high altitudes over the last 100 years. Temperature profiles have been analyzed from boreholes drilled at three different sites between 4240 and 4300 m above sea level in the Mont Blanc area (French Alps). A mean warming rate of 0.14 °C/decade between 1900 and 2004 was found. This is similar to the observed regional low altitude trend in the north-western Alps, suggesting that air temperature trends are not altitude dependent (33).

The more recent warming in the Alps observed since the mid 1980s, while in step with global warming, is roughly three-times greater than the global average. The most significant warming has occurred since the 1990s. In fact, the years 1994, 2000, 2002, and particularly 2003, have been the warmest on record in the past 500 years (7).

The intense warming in the Alps during the 1990s has been linked in part to the behavior of the North Atlantic Oscillation (NOA). The NOA is characterized by cyclical fluctuations in air pressure and changes in storm tracks across the North Atlantic. The NAO is believed to particularly influence climate in high elevation regions in the Alps (8). The influence of the NAO on the decadal trends in the occurrence of atmospheric blocking events was confirmed in a recent study (13).

During the summer of 2003, central Europe suffered an extraordinarily severe heat wave. In the part of Switzerland lying north of the Alps, the mean air temperature in summer (June–August) exceeded the long-term mean (1864–2000) by more than 5 standard deviations), making summer 2003 by far the warmest in this region since instrumental records began in 1864 (24). The 2003 heat wave suggests that climate variability may have increased (12).

Very high temperatures that established a new historical maximum in Austria characterized the European summer of 2013. The most intense 2013 heat wave over Central Europe in early August was driven primarily by anticyclonic conditions and was probably amplified by the preceding precipitation deficit. In combination with major flooding in the Danube and Elbe river basins in early June and severe convective storms at the end of July, the hot 2013 summer in Central Europe may represent an analogue of a future summer climate that will probably be more prone to both temperature and precipitation extremes (35). 

Precipitation changes until now

Unlike temperature, there is no similar long-term trend in precipitation averaged over the Alps in the past 500 years, although a slight decline in average regional precipitation has been observed since about 1970 (9). Strong negative Swiss Alpine snow trends were observed in the late 1980s and 1990s. These trends can be mainly attributed to local temperature increases, the precipitation impact is small (14).

Observations over the period 1971-1994 of the Pannonian region in East Austria do not show a general trend in time and space to shorter or longer dry spells (averages and extremes) (26). Also, for annual precipitation no significant changes could be detected in the spatial and seasonal distribution of precipitation and run-off trends in Austria (27). On a seasonal base, however, the main Alpine ridge clearly separates Austria in two parts. On the northern part an increase in fall and winter is documented and on the southern side a decrease in precipitation and run-off has been observed (27).

The North Atlantic Oscillation (NAO) plays a major role in determining snow pack in Poland and Eastern Europe (15). Alpine high-pressure episodes are linked with the positive phase of the NAO and accompanied by positive temperature anomalies and below average precipitation, both of which are unfavourable for Swiss Alpine snow accumulation.

Extreme events

The results from an analysis of the maxima of long-term (1901–2013) daily precipitation records from a densely sampled Central European station network, spanning Austria, Switzerland, Germany and the Netherlands, support the expected tendency of increasing extreme precipitation intensity with continuing global warming. The increase is approximately 6-8% per degree Celcius, both for short- and long-duration events (39).

Snow cover changes until now

Over the last 50 years (1968–2017), the European Alps have experienced a decline in the winter snow depth and snow cover duration ranging from −7% to −15% per decade and from −5 to −7 days per decade, respectively, both showing a larger decrease at low and intermediate elevations (41). 

The spatial and temporal patterns of mean snow depth between November and April over the period since 1961 have been quantified from 139 stations in Switzerland and Austria. Most strikingly, the southern regions in both Austria and Switzerland are characterized by a clear decrease in mean snow depth (up to -12 cm/decade on the mean at elevations of about 2000 m a.s.l.), whereas the northeastern part of Austria shows no trend for the same period. Low elevation regions (below 1,000 m.a.s.l.) show a high correlation with air temperature and accordingly also temperature sensitivity of snow depth, which decreases with increasing altitude. High elevation sites (above 1,000 m.a.s.l.) show increasing correlation between snow depth and precipitation with altitude, indicating that snow depth changes are forced by precipitation (38).

Glacier changes until now

From 1850 to 1980 glaciers in the Alps lost approximately 30-40% of their area and one half of their mass. Since 1980 until 1995 another 10-20% of the remaining ice has been lost (10). A recent analysis has revealed that 12% of the volume of Swiss glaciers was lost since 1999 (5). Data on the longest and most continuous series for six glaciers in the European Alps (In Austria, Switzerland and France, over the period 1962-2013) show a clear and regionally consistent acceleration of mass loss over recent decades over the entire European Alps (36). 

First results from field measurements indicate that the extreme warm and dry weather conditions in summer 2003 caused an average loss in thickness of glaciers in the European Alps of about 3 meters water equivalent, nearly twice as much as during the previous record year of 1998 (1.6 m), and roughly five times more than the average loss of 0.65 m per year recorded during the exceptionally warm period 1980-2000. In 2003 alone, the total glacier volume loss in the Alps corresponds to 5-10% of the remaining ice volume (18).

Air temperature changes in the 21st century

By the end of the 21st century, relative to the reference period 1981–2010, annual mean temperature in the Alps is projected to be 1 °C, 2 °C, and 4 °C higher under a low-end (RCP 2.6), moderate (RCP 4.5) and high-end (RCP 8.5) scenario of climate change, respectively. Strongest warming is projected for the summer season, for regions south of the main Alpine ridge. Depending on the season, medium to high elevations might experience an amplified warming (40). 

For Austria, climate change data have been produced for the period 2008 – 2040 through linear regression modelling with repeated bootstrapping, based on historical daily weather station data from 1975 to 2007. From these results a mean annual temperature rise was estimated of about 1.6 °C from 2008 to 2040, consistent with the results of other authors (30).

From 1990 to 2050, warming is expected to be similar on the northern and on the southern side of the Alps. According to the mean estimate (median value), temperatures will increase in northern Switzerland by 1.8°C in winter and 2.7°C in summer. Corresponding values for southern Switzerland are +1.8°C in winter and +2.8°C in summer (2,12). The ranges for these values are:

• Winter, north side: 0.9 - 3.4°C increase
• Winter, south side: 0.9 - 3.1°C increase
• Summer, north side: 1.4 - 4.7°C increase
• Summer, south side: 1.5 - 4.9°C increase

For the transitional seasons, warming is expected to be similar to the trend projection for winter (spring: +1.8°C on the northern and the southern side of the Alps; autumn: +2.1°C on the northern side of the Alps, +2.2°C on the southern side of the Alps) (2,12).

In wintertime, the seasonal freezing level (= altitude where surface air temperature is 0°C) has risen by about 200 m per degree of warming from approximately 600 m in the 1960s to approximately 900 m in the 1990s (3). If warming in winter continues as expected, the freezing level will further rise by about 180 m until 2050 in case of moderate warming (+0.9°C), by about 360 m in case of medium warming (+1.8°C), and by about 680 m in case of strong warming (+3.4°C) (4). The freezing level roughly corresponds to the height of the snow line (the lower limit of the snow cap).

Under the A1B scenario, the simulated annual mean warming from 1980–1999 to 2080–2099 varies from 2.2 to 5.1°C with a median of 3.5°C (17).

Climate models show a more significant increase in absolute maximum temperatures than in mean daily maxima. Conditions as during the summer 2003 heat wave will still be rare events in case of moderate warming, but will occur every few decades in case of medium warming, and every few years in case of strong warming. Extremely hot summers will occur more frequently if, additionally, year-to-year variability of summer temperatures increases, as various climate simulations suggest (1).

By contrast, the frequency of cold spells and the number of frost days have already declined and will continue to decline. In winter, the daily temperature variability is likely to become smaller because minimum temperatures are projected to rise more strongly than mean temperatures (1).

Precipitation changes in the 21st century

An increase in mean winter precipitation of 8% compared to 1990 is expected north of the Alps by 2050 (11% south of the Alps), and a decrease of 17% in summer (19% south of the Alps) with respect to 1990 values. In spring and in autumn the trends for precipitation are small. The magnitude of uncertainty is largest for trends in summer (1,12). The ranges for these values are:

• Winter, north side: 1% decrease – 21% increase
• Winter, south side: 1 – 26% increase
• Summer, north side: 7 – 31% decrease
• Summer, south side: 6 – 36% decrease

The frequency of heavy and extreme precipitation events may increase in central and northern Europe in winter. At altitudes above 2000 m, more frequent heavy precipitation events in winter would lead to higher amounts of snowfall in short periods of time. This may increase the danger of avalanches. An increase in heavy precipitation in central Europe may also occur in spring and autumn. For summer, the situation is less clear (4). The more relevant extreme events such as those with 10-year return period remain in summer and increase strongly in intensity (37).

Snow cover changes in the 21st century

It is estimated that 1°C rise in temperature would reduce the snow cover duration by up to several weeks (22), even at high altitudes. A 4°C warming would reduce the snow volume by 90% at 1000 m, and 30–40% at 3000 m in Switzerland (23).

A recently-published study on the sensitivity of the Alpine snow cover to temperature reported a distinctive and strong variation of snow-cover sensitivity to temperature change with altitude (28). The study estimated that a 1°C increase in temperature over central Europe would result in a reduction of about 30 days in snow duration (snow cover of at least 5 cm) in winter at the height of maximum sensitivity (about 700 m). Snowfall in lower mountain areas is likely to become increasingly unpredictable and unreliable over the coming decades (29).

Changes in mean winter snow water equivalent (SWE), the seasonal evolution of snow cover, and the duration of the continuous snow cover season in the European Alps have been assessed from an ensemble of regional climate model (RCM) experiments under the IPCC SRES A1B emission scenario. The assessment was carried out for the periods 2020–2049 and 2070–2099, compared with the control period 1971–2000. The strongest relative reduction in winter mean SWE was found below 1,500 m, amounting to 40–80 % by mid century relative to 1971–2000 and depending upon the model considered. At higher elevations the decrease of mean winter SWE is less pronounced but still a robust feature. For instance, at elevations of 2,000–2,500 m, SWE reductions amount to 10–60 % by mid century and to 30–80 % by the end of the century (34).

Glacier changes in the 21st century

The area covered by alpine glaciers may diminish by about 75% in case of medium warming by 2050. In case of moderate warming the loss in glacier area will still be as much as 50% and in case of strong warming it will reach 90%, respectively. The relative losses will be smaller than average for large glaciers and larger than average for small glaciers. It is likely that many small glaciers will disappear (4).

Small glaciers will disappear, while larger glaciers will suffer a volume reduction between 30% and 70% by 2050 (19). According to recent research the Alps could lose almost all of their glacier cover by the year 2100 if summer air temperatures increase by 5°C (11,20). Regions below 2,500 m will be ice free by the end of the 21st century (21).

Projections of glacier mass balance in 2100 have been made for five Austrian glaciers (32); these projections have been generated from ensembles of general circulation model (GCM) simulations by the use of direct statistical downscaling, and are based on IPCC-SRES scenarios A1B and B1. The downscaled scenarios show a pronounced retreat of the investigated Austrian glaciers until the end of the 21st century. During winter, the glaciers are projected to gain less mass than during previous decades. In summer, projections suggest large losses (32). Based on these scenarios A1B or B1 a mass balance reduction of 500 mm water equivalent is to be seen towards the end of the 21st century. Differences in the mass balances between these scenarios are small until 2050. Differences however get larger during the second half of the century; the estimations for the A1B emission scenario would give reason for reductions that are twice as large as those caused by the B1 emission scenario (32).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Austria.

1. Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
2. Frei (2004), in: Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
3. Scherrer and Appenzeller (2006), in: Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
4. OcCC (2007), in: Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
5. Farinotti et al. (2009), in: Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
6. OcCC (2008), in: Federal Office for the Environment FOEN of Switzerland (Ed.) (2009)
7. Beniston (2005), in: Agrawala (2007)
8. Beniston (2000), in: Agrawala (2007)
9. Casty et al. (2005), in: Agrawala (2007)
10. Haeberli and Hoelzle (1995), in: Agrawala (2007)
11. Zemp et al. (2006), in: Agrawala (2007)
12. Thommen Dombois and Braun-Fahrländer (2004)
13. Scherrer et al. (2006), in: Scherrer and Appenzeller (2006)
14. Scherrer et al. (2004), in: Scherrer and Appenzeller (2006)
15. Clark et al. (1999); Bednorz (2002), both in: Scherrer and Appenzeller (2006)
16. Beniston (1997), in: Scherrer and Appenzeller (2006)
17. Bogatai (2007)
18. UNEP (2004)
19. Schneeberger et al. (2003); Paul et al. (2004), both in: Alcamo et al. (2007)
20. Haeberli and Burn (2002), in: European Environment Agency (EEA) (2005)
21. Paul et al. (2004), in: European Environment Agency (EEA) (2005)
22. Hantel et al. (2000), in: European Environment Agency (EEA) (2005)
23. Beniston (2003), in: European Environment Agency (EEA) (2005)
24. Schär et al. (2004), in: Jankowski et al. (2006)
25. Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
26. Nobilis and Weilguni (1997), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
27. Fürst et al. (2007), in: Federal Ministry of Agriculture, Forestry, Environment and Water Management (2010)
28. Hantel and Hurtl‑Wielke (2007), in: EEA, JRC and WHO (2008)
29. Elsasser and Bürki (2002), in: EEA, JRC and WHO (2008)
30. Eitzinger et al. (2009); Gobiet et al. (2009), both in: Strauss et al. (2013)
31. Nemec et al. (2013)
32. Springer et al. (2013)
33. Gilbert and Vincent, (2013)
34. Steger et al. (2013)
35. Lhotka and Kyselý (2015)
36. Vincent et al. (2017)
37. Brönnimann et al. (2018)
38. Schöner et al. (2019)
39. Zeder and Fischer (2020)
40. Kotlarski et al. (2023)
41. Monteiro and Morin (2023)