50. Poland - temperature trends WARMING 0.9°C

There are over 100 temperature records for Poland. The longest is the Warsaw record (Berkeley Earth ID: 157587) which dates back to 1779 (see Fig. 50.1 below) and exhibits a strong warming trend of 0.71 °C per century. However, this warming trend is not continuous but has considerable variability, with temperatures in the 1930s being comparable to those of today.

 

Fig. 50.1: The temperature trend for Warsaw since 1779. The best fit is applied to the interval 1811-2010 and has a positive gradient of +0.71 ± 0.08 °C per century. The monthly temperature changes are defined relative to the 1951-1980 monthly averages. 

 

Of the 100 or more stations in Poland (for a full list see here), 60 have over 480 months of data (these are medium stations) and five have over 1200 months of data (long stations). In fact over 40 of the medium station have over 720 months (or 60 years) of data which is fairly unusual. This is because there was a significant and abrupt increase in the number of weather station records in Poland in 1951. Similar investments in new stations are seen in many other countries as well in the latter part of the 20th century, but these tend to occur around 1960 or 1970-1973.

The locations of these long and medium stations are shown below in Fig. 50.2. The map indicates that the stations are fairly evenly distributed across Poland which means that a simple average of the anomalies from all these stations should approximate very well to the temperature trend for the country as a whole.

Fig. 50.2: The locations of long stations (large squares) and medium stations (small diamonds) in Poland. Those stations with a high warming trend are marked in red. 

 

In order to determine the mean temperature change for Poland, I first calculated the temperature anomalies for each temperature record relative to its monthly means (MRTs) for the period 1951-1980. These anomalies were then averaged to produce the trend shown in Fig. 50.3 below.

The 1951-1980 interval was chosen because it allowed the maximum number of stations to be included in the mean (see Fig. 50.4 below) while also avoiding the sudden jump in temperatures seen around 1988 in many European temperature records (see Post 44 and Post 49) that could destabilize the MRTs. For a moredetailed description of how the monthly reference temperatures (MRTs) are calculated and why, please refer to Post 47.

 

Fig. 50.3: The temperature trend for Poland since 1779. The best fit is applied to the interval 1811-2010 and has a positive gradient of +0.45 ± 0.08 °C per century. The monthly temperature changes are defined relative to the 1951-1980 monthly averages. 

While the trend in Fig. 50.3 above is the result of averaging over 60 separate records, no more than 58 are included in any single monthly average, and before 1950 this is typically less than ten (see Fig. 50.4 below). Overall, the temperature trend exhibits a significant warming of about 0.9 °C since 1800, but this is much less than that seen in the trend for Warsaw as shown in Fig. 50.1 above. The difference is almost certainly due to anthropogenic effects such as the urban heat island (UHI) effect or waste heat emissions from human and industrial activity. Overall such direct anthropogenic surface heating (DASH) would be expected to increase the temperature of the whole of Poland by about 0.2 °C.

The other detail that is noticeable about the data in Fig. 50.3 is that the temperatures in the 1930s were similar to those of today. This is despite temperatures appearing to have jumped suddenly by about 0.84 °C in 1988. A similar and larger jump of 0.97 °C was seen in the temperature data across Germany at the same time (see Post 49).

Fig. 50.4: The number of station records included each month in the mean temperature trend for Poland when the MRT interval is 1951-1980.

What is clear is that the warming seen in Poland, while significant, is much less than that expected based on IPCC and Berkeley Earth reports. These have suggested that the warming is over 1.5 °C and fairly monotonic. In reality there is a large amount of what looks like natural variation in the data that persists even for very long time-averaged data such as the 5-year moving average.

Fig. 50.5: Temperature trend in the Poland since 1779 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 1801-1980 and has a gradient of +0.32 ± 0.03 °C/century.

For comparison, the temperature trend that results from averaging the temperature data after it has been adjusted by Berkeley Earth is shown in Fig. 50.5 above. This trend shows a modest warming of 0.32 °C per century before 1980, or about 0.6 °C in total, followed by a major temperature increase of over 1 °C after 1980. This trend is also virtually identical to the one published by Berkeley Earth (see here) as shown in Fig. 50.6 below.

Fig. 50.6: The temperature trend for Poland since 1750 according to Berkeley Earth.

If we look at the difference between the mean trend in Fig. 50.3 (based on the original true data) and the trend in Fig. 50.5 that is the result of using the Berkeley Earth adjusted data we see that the adjustments made by Berkeley Earth are again not neutral. In fact the Berkeley Earth adjustments add nearly 0.6 °C of warming since 1840 (see Fig. 50.7 below).

Fig. 50.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 50.5 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 1841-2010 has a gradient of +0.335 ± 0.007 °C per century. The orange curve shows the contribution from breakpoint adjustments.

Conclusions

It is clear from the results shown here that temperatures in Poland have increased over the last 250 years, but by how much and for what reason remains unclear. There has certainly not been the catastrophic warming due to carbon dioxide emissions (i.e. more than 1.5 °C) that has been claimed by climate scientists, although there might have been some warming from this source. However, such warming cannot realistically be greater than 0.7 °C (i.e. the 0.9 °C seen in Fig. 50.3 minus the 0.2 °C we would expect from DASH or UHI effects). The problem is that any remaining warming that may be due to CO₂ emissions does not correlate well with CO₂ levels in the atmosphere over time. And then there is the uncertainty over the amount that natural variation in the temperature record may be contributing to the relatively short-term trends (less than 250 years) that we are observing.

We can probably claim with a fair degree of confidence that the data after 1950 in Fig. 50.3 is likely to be highly reliable as it is based on over 50 station records that are evenly spaced geographically (see Fig. 50.2). But this raises the question of what is causing the sudden jump in temperatures seen in 1988 which is also seen in other countries such as Germany (see Post 49).

For data before 1950, this is based on between about four and ten station records, at least back to 1830. The overall trend for 1831-1980 suggests a total temperature rise of only about 0.35 ± 0.15 °C, which is less than the standard deviation of the temperature fluctuations in the 5-year moving average for that period. This suggests that these temperature changes could be explained by natural variability.

Finally, it is apparent that once again there is a large discrepancy (0.6 °C) between any temperature rises seen in the raw data (see Fig. 50.3) and the rises claimed by climate scientists (see Fig. 50.5). This difference is largely due to adjustments made to the raw data by climate scientists (see Fig. 50.7).