Climate Change in Switzerland

The climate in Switzerland is characterised by large natural fluctuations. However, certain changes that have taken place since industrialisation can only be explained in terms of the increase in greenhouse gases. The average annual temperature has seen an increase of around 2°C since 1864 (as by 2018), for the most part in the last few decades. Most notably, there has been significantly less snow since the 1980s, and some changes in precipitation are now becoming apparent. According to current climate scenarios, the warming will continue into the future. Summers are becoming drier, and extreme weather events are increasing

The weather and its statistical characteristics, the climate of Switzerland, have been systematically monitored and measured for over 150 years. These data and careful processing of them are essential for being able to better understand climatic fluctuations and climate change, and to develop models that can give us a picture of how the climate will change in the future. In collaboration with partners, MeteoSwiss develops future climate scenarios on a regular basis. This is indispensable to adapt and evaluate the risks and opportunities associated with climate change.

Historic climate: Natural fluctuations and climate change

Weather observations and measurements from around the world indicate that climate is characterised by large fluctuations. Until the beginning of the 20th century, these fluctuations were primarily due to natural causes. Later on, there are effects, in particular the temperature rise of the last few decades, that can only be explained in terms of the increasing greenhouse gas emissions (climate change). The long temperature data series from Basel since 1755 (Figure 1) illustrates this situation very clearly: Natural fluctuations dominate the temperature up to the beginning of the 20th century. The steep temperature rise in the last few decades, on the other hand, is a consequence of the increasing greenhouse gas emissions (climate change).

Observed trends for temperature, precipitation and sunshine

The effects of climate change are evidenced in numerous weather parameters - with the most obvious being temperature. The atmosphere close to the ground has warmed by around 2°C since measurements began in 1864. That is more than twice the rise in the average global temperature of around 0.9°C (as of 2018). For around 30 years, there has not been one year that has been cooler than the average temperature between the period of 1961-1990. Nevertheless, the temperature fluctuates from year to year, as shown in figure 2.

Observed trends for temperature, precipitation and sunshine

Precipitation, too, has changed in some regions. The average winter precipitation over the last 150 years has risen in most regions in Switzerland (with the exception of the southern Alps and large areas of Grisons). So far, no changes have been evident in the average summer precipitation. There are clear indications, however, that heavy precipitation events are slowly changing, as the intensity as well as the frequency of heavy precipitation events (daily totals) have increased since 1901. Nowadays, primarily in the low-lying areas, there are significantly fewer days with snowfall, and smaller amounts of new snow falling than 30 to 40 years ago. The number of hours of sunshine dropped significantly between 1950 and 1980. Since 1980, however, the trend is positive, and hours of sunshine are similar today to what they were at the beginning of the 20th century.

More hot days and frost days, earlier vegetation, more drought?

The observed increase of 2°C is a figure that is difficult for people to conceptualise. It is easier to gain a sense of the changes through figures (so-called climate indicators) that everyone is familiar with. For example, everyone knows what a summer's day feels like. So, temperature indicators are already showing significant changes: Summer days and hot days (maximum temperature equal to or higher than 25°C/30°C respectively) have seen a huge increase, while ice and frost days (maximum temperature lower than 0°C/minimum temperature lower than 0°C) have dropped substantially. As a consequence of rising temperatures, spring and summer development of vegetation is occurring significantly earlier nowadays than several decades ago. Whether drought is on the increase is at present not yet conclusive.

The climate of the future: Change will continue

Together with its partners, MeteoSwiss has been producing climate scenarios for some 10 years, which show possible ways in which Switzerland's climate will develop. These are generated by means of complex physical climate models and the employment of modern statistical methods. The current CH2011 scenarios were produced in 2011. These will be replaced by a new generation of scenarios at the end of 2018 (CH2018).

Warmer, drier summers and more extreme weather

Climate change is set to continue into the future, and its effects will grow in intensity. To what extent the climate will change depends first and foremost on future global greenhouse gas emissions: If emissions continue to rise, the temperatures will increase by between 2.5°C and 5.1°C by the end of the 21st century (2085) in comparison with the average temperature for the period 1981-2010. Switzerland will also have to reckon with changes in terms of extreme weather, for example in the form of more heat waves and heavy precipitation events, and fewer cold periods. 

The effects of climate change vary tremendously depending on the future emissions scenario. Table 1 shows that if greenhouse gases emissions are reduced significantly, and the consequent limiting of global warming is kept well under 2°C compared to pre-industrial levels (in accordance with the so-called «Paris Agreement»), changes in tropical nights, hot days and the altitude of the zero-degree line in Switzerland would be significantly smaller than they would be if greenhouse gas emissions continued to rise (the so-called A1B scenario).

 

Table 1: Tropical nights, hot days, zero-degree line yesterday, today, tomorrow
parameter 1960 today around 2085
GGE significantly reduced
around 2085
lrise in GGE until 2050

tropical nights

0

1-2

<5

20

hot days

2-3

10-15

<15-20

30-40

zero-degree line

600

900

<1200

1500

  1. Table 1: The number of average tropical nights (Tmin≥20°C) and hot days (Tmax≥30°C) in central Switzerland and the altitude of the zero-degree line (in m above sea level) around 1960, today (2017) and 2085 shown for a scenario in which greenhouse gas emissions (GGE) are massively reduced (green) and a scenario in which GGE increase until 2050 (red).

Overview of observed and future climate change

Figure 3 summarises the effects of climate change on the typical weather parameters and phenomena of Switzerland. It shows which changes are already evident in the observed data, and what the models for the future are predicting. While climate change has a marked influence on certain parameters (e.g. temperature and snow), the effects on others are less pronounced (e.g. precipitation) or not at all clear (e.g. wind, thunderstorms, hail). It is noteworthy that, with the exception of summer precipitation and corresponding drought, all changes that current climate scenarios indicate are already being observed, at least in their beginnings.

References

Scherrer, S.C., E.M. Fischer, R. Posselt, M.A. Liniger, M. Croci-Maspoli, R. Knutti, 2016: Emerging trends in heavy precipitation and hot temperature extremes in Switzerland, J. Geophys. Res. Atmos., 121, doi:10.1002/2015JD024634.

Scherrer, S.C., M. Begert, M. Croci-Maspoli, C. Appenzeller, 2015: Long series of Swiss seasonal precipitation: regionalization, trends and influence of large-scale flow, Int. J. Climatol., doi:10.1002/joc.4584.

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