56. Switzerland - temperature trends STRONG WARMING 2°C

The temperature trend for Switzerland is qualitatively very different from that of most of its neighbours. The warming is continuous from 1750 onwards (see Fig. 56.1 below) with a trend of +0.46 °C per century up until 1985. This equates to about 1 °C of warming before 1985. The main similarity it shares with the trend from other central European counties (Germany, Austria, Hungary, Czechoslovakia) is the abrupt jump in temperatures around 1988. This adds an additional 0.9 °C of warming compared to temperatures between 1961 and 1980. So in total there is over 2 °C of warming from 1750 until 2010.

Fig. 56.1: The temperature trend for Switzerland since 1750. The best fit is applied to the interval 1756-1985 and has a positive gradient of +0.46 ± 0.05 °C per century. The monthly temperature changes are defined relative to the 1981-2010 monthly averages.

The trend in Fig. 56.1 was determined by averaging the anomaly time series from the 38 longest temperature records in Switzerland and Leichtenstein (for a list see here), although there is only one significant station in Leichtenstein: Vaduz. Each monthly anomaly was calculated relative to the 1981-2010 average temperature for that month of the year. For a more detailed explanation of monthly reference temperatures (MRTs) and how anomalies are calculated, go to Post 47. 

Of these 38 records, six are long stations with over 1200 months of data and twelve are medium stations with over 480 months of data. Unusually, Switzerland also has a significant number of stations with between 360 and 480 months of data: twenty in total. As this is more than the number of long and medium stations combined, and as the length of these records is still significant, they too were included in the trend calculation in Fig. 56.1.

Fig. 56.2: The number of station records included each month in the mean temperature trend for Switzerland when the MRT interval is 1981-2010.

The number of stations used to determine the mean temperature each month in Fig. 56.1 is shown in Fig. 56.2 above. In addition, the locations of the long and medium stations are indicated in Fig. 56.3 below. It can be seen that almost all the station temperature time series have a warming trend, and the long stations are mainly located near to the major cities.

Fig. 56.3: The locations of long stations (large squares) and medium stations (small diamonds) in Switzerland. Those stations with a high warming trend are marked in red. Those with cooling or stable trends are marked in blue.

If we now look at the Berkeley Earth version of the temperature trend we see a rather different picture. The trend is virtually flat before 1985, with a sudden jump of over 1 °C occurring in 1987 (see Fig. 56.4 below). This means that Berkeley Earth are only claiming about 1 °C of warming in Switzerland since pre-industrial times, whereas the raw data in Fig. 56.1 suggest the true value is double that. One caveat to this, however, is that the temperature time series in Fig. 56.4 does show a dip in temperatures of almost 0.5 °C is the 19th century. So if the trend is measured from about 1850, the total warming is probably about 1.5 °C, and thereby in line with IPCC claims for the Northern Hemisphere.

Fig. 56.4: Temperature trend in Switzerland since 1750 derived by aggregating and averaging the Berkeley Earth adjusted data for all long and medium stations. The best fit linear trend line (in red) is for the period 1756-1985 and has a gradient of +0.06 ± 0.02 °C/century.

The temperature trends in Fig. 56.4 above are once again almost identical to the official Berkeley Earth version shown below in Fig. 56.5. So the difference between the trends in Fig. 56.1 and Fig. 56.4 cannot be in the averaging process. It must be due to the adjustments.

Fig. 56.5: The temperature trend for Switzerland since 1750 according to Berkeley Earth.

These adjustments are shown in Fig. 56.6 below. Unusually they have a negative trend, indicating that they actually reduce the overall trend rather than adding to it. In fact the total reduction can be viewed as being between 1 °C and 1.25 °C, depending on the time interval chosen.

Fig. 56.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 56.4 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1756-1985 has a negative gradient of -0.398 ± 0.005 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

Summary

1) The climate in Switzerland appears to have warmed more than neighbouring countries (Germany, Austria, etc) since 1750. The warming of 2 °C is even more than is seen in the IPCC global trend.

2) Part of the warming is due to a sudden jump in temperatures of approximately 0.9 °C that occurred in the mid-1980s (see Fig. 56.1). This is similar to the jumps seen in equivalent trend data for neighbouring countries (Germany, Austria, Hungary, Czechoslovakia).

3) Unlike its neighbours, Switzerland appears to have experienced significant and continuous warming of over 1 °C from 1750 to 1980 (see Fig. 56.1)

4) The temperature trend based on Berkeley Earth adjusted data shows no warming before 1985 (see Fig. 56.4), although there is significant variation in the trend with temperatures in the 18th century higher than those in the 19th century.