Climate change Switzerland
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).
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 (40).
In the 20th century, the temperature increase was about 1.6°C in western Switzerland, about 1.3°C in the German-speaking part of Switzerland and about 1°C south of the Alps. North of the Alps, the frequency of abnormally warm months, that is, months with an average temperature more than 2 °C above the long-term mean, had already increased by about 70% (33). An increase of more than 1°C in average temperature has been observed in Austria during the last century (25).
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).
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)
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).
Precipitation changes until now
Annual rainfall in Switzerland increased by about 120 mm (8%) during the 20th century. In the northern and western part of the alpine area, mean winter precipitation increased by about 20 to 30% (34). Heavy daily precipitation and heavy precipitation lasting between 2 to 5 days increased in autumn and winter in large parts of the midlands and the northern edge of the Alps (35). Since evaporation rose in parallel to the warming by 105 mm (23%), the mean annual runoff remained virtually the same.
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).
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.
Annual maximum snow depth and snowfall data from 25 stations (between 200 and 2,500 m), collected during the 80 winters between 1930/31 and 2009/2010), show a decrease in extreme snow depth, which is mainly significant at low altitudes (below 800 m). A negative trend is also observed for extreme snowfalls at low and high altitudes but the pattern at mid-altitudes (between 800 and 1,500 m) is less clear. The decreasing trend of extreme snow depth and snowfall at low altitudes seems to be mainly caused by a reduction in the magnitude of the extremes rather than the scale (variability) of the extremes. This may be caused by the observed decrease in the snow/rain ratio due to increasing air temperatures. In contrast, the decreasing trend in extreme snow depth above 1,500m is caused by a reduction in the scale (variability) of the extremes and not by a reduction in the magnitude of the extremes. However, the decreasing trends are significant for only about half of the stations and can only be seen as an indication that climate change may be already impacting extreme snow depth and extreme snowfall (37).
Data on new snow sum and days with snowfall over the period 1864-2009 show large decadal variability (44). For low stations in the Swiss Alps the lowest values were recorded in the late 1980s and 1990s; for higher stations the values of late 1980s and 1990s are at least among the lowest since the late 19th century. The amount of maximum new snow shows no clear trend over this 145 year period, however. There are changes in the Swiss Alpine snow pack that may be due to climate change. However, the complex local influences on the snow pack via temperature, precipitation, radiation, wind and humidity and the large decadal variability in the mid-latitude climate system makes it difficult to understand the details of changes in Swiss Alpine snow pack (44).
Snow cover duration
Snow cover duration and maximum snow depth have clearly been declining in the Swiss Alps since 1970, irrespective of elevation and location. This is most likely due to the increase in temperatures observed at all elevations in the Swiss Alps, especially during spring (51). In the European Alps a rapid temperature increase was observed since the 1980s, particularly in spring (52). As a result snow cover duration in the European Alps has reduced (53). This reduction can be due to accelerated snowmelt in spring (54) and/or reduced snowfalls during the winter season (55). The latter could be the consequence of a decrease in the snow/rain ratio, as observed in the Swiss Alps in winter (56), late autumn (57) and spring (57,58).
Snowpack characteristics have been analysed for the Swiss Alps over the period 1970-2015 at eleven meteorological stations, spanning elevations from 1139 to 2540 metres above sea level. Overall, the results demonstrate a marked decline in all snowpack parameters, irrespective of elevation and region, and whether for drier or wetter locations, with a pronounced shift of the snowmelt in spring, in connection with reinforced warming during this season (51).
The duration of a continuous period of snow cover varies with elevation from 108 to 260 days. Since 1970, snow cover duration has significantly shortened at all sites, on average by 8.9 days per decade. This shortening was largely driven by earlier snowmelt (on average 5.8 days per decade). On average, the snow season now starts 12 days later and ends 26 days earlier than in 1970. This corresponds to a shortening of 2.6 to 7.5 % per decade (51).
The number of days with snow on the ground has decreased at all elevations and in all regions of the Swiss Alps. This decrease was significant at all stations for a snowpack of at least 1 cm: the number of days with snow on the ground reduced by 4.5 to 11.1 days per decade. For larger snow depths somewhat different results were obtained. The number of days with a snowpack of at least 100 cm, for instance, reduced by 0.8 to 13.2 days per decade, but this reduction was statistically significant at only four stations (51).
Mean maximum snow depth varied from 65 to 353 cm over the study period. Overall, the annual maximum snow depth has declined since 1970 by 3.9 to 10.6 % per decade. Warmer temperatures and later snow onset in autumn contribute significantly to the reduction of the maximum snow amounts that can then be reached during the winter (51).
The observed snowpack reduction is most likely related to the general increase in temperatures observed at all elevations in the Swiss Alps, especially during spring. The differences in observed changes in snow onset and snowmelt dates are coherent with the differences in seasonal temperature trends in the Swiss Alps, showing a stronger increase in spring (+0.84°C per decade) than in autumn (+0.21°C per decade) since the 1970s (57,59). The impact of global warming on snowpack may have been additionally enhanced by an increasing trend in sunshine duration, observed at both low and high elevations in the European Alps from 1975 to 2000 (60).
Wind climate changes until now
Measured wind gust speeds have increased strongly in Switzerland since the beginning of records in 1933 (36).
Ice cover changes rivers and lakes until now
A study on ice cover information from 11 Swiss lakes over the last century has shown that ice cover was significantly reduced in the past 40 years, and especially during the past two decades (28).
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 (61).
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
Updated climate change calculations, made in 2011, project seasonal mean temperature increase of 3.2–4.8°C (A2 scenario) and 2.7–4.1°C (A1B scenario) by the end of the century (2085) for all Swiss regions, with respect to 1980-2009. For the stabilization scenario (emissions cut by about 50% by 2050), Swiss climate would still change over the next decades, but is projected to stabilize at an annual mean warming of 1.2–1.8°C. Uncertainties due to climate model imperfections and natural variability typically amount to about 1°C in temperature. For 2035 projected temperature increase is 0.9–1.4°C (A1B scenario). For 2060 projected temperature increase is 2.0–2.9°C (A1B scenario) (32,39).
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).
Differences lowlands - Alps
Warming is stronger in the Alps than in the Swiss lowlands (according to several scenarios and regional climate models): about 1 °C for the summer in the second half of the 21st century compared with 1980–2009 (45). This altitude-dependence of temperature change is likely related to the snow-albedo (less snow at higher elevations means more warming) and other feedback mechanisms (46). Projections indicate warming of about 1 to 6 °C for the Alps until the end of the 21st century, strongly depending on the scenario and the lead time (45).
Differences northern - southern side of the Alps
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).
Heat waves and cold spells
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 (1,31). 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
Most global climate models (GCMs) project a ubiquitous decrease in summer precipitation over the Alps in response to global warming. The resolution of these models is coarse, probably too coarse to get a good indication of how precipitation in the Alps may change this century. In fact, high-resolution regional climate models project enhanced summer convective rainfall at Alpine high elevations in response to climate warming (49,63). This increase of (intense) summer rainfall is not projected in the global climate models and is important for fresh water supply and, for instance, with respect to flash floods. The increase of summer convective rainfall was projected for near term (2010 – 2039), mid-century (2040 – 2069 and late century (2070 - 2099), with respect to 1975 – 2004, and based on several different models and a high-end scenario of climate change (the so-called RCP8.5 scenario). This precipitation increase is qualitatively consistent with positive trends in observed (extreme) precipitation increase over the Swiss Alps (50), although these trends may also be due to natural variability.
Updated climate change calculations, made in 2011, project summer mean precipitation decrease by the end of the 21st century (2085) by 21–28% (A2 scenario) and 18–24% (A1B scenario), with respect to 1980-2009. For the stabilization scenario (emissions cut by about 50% by 2050), summer drying would be of 8–10% by the end of the century. Uncertainties due to climate model imperfections and natural variability typically amount to about 15% in precipitation (32,39).
The projected summer drying over Switzerland at the end of the century (according to several regional climate models and the A1B emission scenario) is associated with a strong decrease in the number of wet days whereas changes in wet-day intensity are smaller. Wet days are days with daily precipitation equal or above 1 mm per day; wet-day intensity is average daily precipitation amount on all wet days in the summer. Over the lowland regions (north and south of the Alpine ridge), a decrease in wet-day frequency of more than 17% in 2070-2100 compared with 1980-2010 is projected, whereas over the two Alpine regions the decrease is smaller lying between approximately −11 and −15%. In the winter season, there is generally a tendency for precipitation to intensify over almost all of Switzerland (47).
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). In the Alps the more relevant extreme events such as those with 10-year return period remain in summer and increase strongly in intensity (63).
Differences lowlands - Alps
A height-dependence of the precipitation change signal is found in many seasons: model results indicate a stronger increase in precipitation at low altitudes in the winter as compared to the Alpine region, but a tendency towards more drying at lower compared with higher altitudes in the summer. In case of precipitation, the projection uncertainty is large, however, and in most seasons precipitation can increase or decrease (45).
Differences northern - southern side of the Alps
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. These have been confirmed by (31). 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
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 (29). 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 (30).
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 (41). Similar results have been reported based on ten regional climate models and this same A1B emission scenario (48): at the end of the century, mean snow depth/SWE are reduced by 35/32%, 83/86% and 96/97% at high-, mid- and low-elevations, respectively. The low-elevation stations already show a strong decrease in the near future (2020–2049). Different future projections have also been reported for the Swiss Alps, however, such as more abundant snowfall in the Alps in the higher reaches of the mountains, much reduced snow at lower levels, and the crossover level where snow becomes more abundant under milder conditions being located between 1700 and 2000 m above sea level (38).
Wind climate changes in the 21st century
No robust projection for extreme wind storms in Switzerland is possible; severe changes, however, cannot be ruled out (32).
Climate indices changes in the 21st century
Future development of some key climate indices over Switzerland have been evaluated for the end of the century (2070-2099) with respect to the reference period 1980–2009 (42), based on previously published data on projected temperature and precipitation change (43) (under the emission scenarios A1B, A2, and RCP3PD). For the end of the century the model results indicate:
- a doubling of the number of summer days (under the scenarios A1B and A2); summer days are days with maximum temperatures ≥ 25°C.
- an appearance of tropical nights even above 1500 m asl; tropical nights are nights with minimum temperatures ≥ 20°C.
- a possible reduction of the number of frost days by more than 3 months at altitudes higher than 2500 m asl; frost days are days with minimum temperatures < 0°C.
- a decline of the number of ice days by about 90 days above 3000 m asl; ice days are days with maximum temperatures < 0°C.
- a prolongation by roughly 50 days of the thermal growing season length in the lowest parts of Switzerland (under the scenarios A1B and A2); the thermal growing season length is the average number of days in a year between the first occurrence of a 6-day period with daily mean temperatures > 5°C and the first occurrence after July 1 of a 6-day period with daily mean temperatures < 5°C.
- a decline of heating degree days by about 30% until the end of the century; heating degree days are the annual average sum of differences between outside daily mean air temperature and the base temperature inside the building (20°C).
- a likely increase of cooling degree days by about a factor 3 compared to present levels in the Swiss lowlands (under the scenarios A1B and A2); cooling degree days are the annual average sum of differences between outside daily mean air temperature and the base temperature of 18.3°C, above which cooling is assumed to be needed in buildings.
- the near disappearance of days with fresh snow at low altitudes; defined as days with a minimum of 1 cm snowfall.
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).
Slow down retreat Morteratsch Glacier by artificially produced snow
A feasibility study shows that the retreat of the Morteratsch Glacier in Switzerland can be slowed down by artificially produced summer snow, thus extending the ‘lifespan’ of this touristic attraction (62).
In Switzerland, the Morteratsch Glacier is a major touristic attraction. The glacier is currently about 6 km long, and spans an altitudinal range of about 2200 to 4000 m. Due to strong retreat the lowest part of the glacier is getting out of sight from the gravel road that provided direct access to the glacier front. The local community wondered whether measures could be taken to slow down the retreat of this glacier in an environmentally friendly way. The effect was studied of artificially producing snow on the glacier in the summer to slow down its retreat, covering an area of 0.8 km2 in the higher ablation zone. In addition to adding mass to the glacier, artificial snow has the advantage of increasing the albedo and thus reducing the amount of energy available at the surface for melting. Lakes in the surrounding area can provide the water. The study was based on a model of the dynamics of the glacier and a 20-year weather station record from the lower part of the glacier (62).
The main conclusion of the study is that deposition of artificial snow on the Morteratsch Glacier can have a significant effect on the future evolution of the glacier. It takes about 10 years before the snow deposition starts to work out on the position of the glacier snout. Then the snow deposition appears to become effective. Under a scenario of modest global warming, the difference in glacier length between model calculations with and without artificial snow is 400 to 500 m within two decades. Thus, keeping an area of 0.8 km2 covered by snow for many decades is an enormous and expensive task, but it may be technically possible (62).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Switzerland.
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