Tuesday, January 31, 2023

150: Malta - temperature trends STABLE before 1980

The difficulty in determining the extent of climate change in Malta is the lack of data. According to Berkeley Earth (BE) there are only two stations with over 480 months of data and one of those (A. M. D.) has virtually no data after 1934. The other station is Luqa (BE ID:156721) which is situated near the main airport and actually has over 1800 months of data, so it could be a good indicator of the climate of Malta as a whole. Its monthly mean temperature anomaly (MTA) relative to the period 1981-2010 is shown in Fig. 150.1 below.

 

Fig. 150.1: The mean temperature change for Luqa since 1840 relative to the 1981-2010 monthly averages. The best fit is applied to the monthly mean data from 1881 to 1980 and has a slight positive gradient of +0.05 ± 0.11 °C per century.

 

The data in Fig. 150.1 indicates that there was virtually no climate change in Malta before 1980. Then after 1980 the local temperature appears to have risen by about 0.6°C, although this depends on how one interprets the data. If one uses the 5-year average (yellow line) as a guide the temperature appears to increase by over 1°C from 1880 to 2010. However, average temperatures in 2010 are only about 0.6°C above the 1881-1980 best fit line (in red) which is virtually horizontal. So this would indicate that temperatures in 2010 are only about 0.6°C above average.

 

Fig. 150.2: Temperature trends for Luqa based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1886-2010 and has a positive gradient of +0.56 ± 0.03°C/century.

 

A similar temperature trend for Luqa is seen in its Berkeley Earth (BE) adjusted data (see Fig. 150.2 above) which appears to have zero adjustments after 1870. However, the actual published BE trends for Malta shown in Fig. 150.3 below appear to exhibit more warming over the period from 1890 to 2000 (~1.6°C) than is seen in the Luqa data in Fig. 150.2 (~1.4°C). It is also interesting that the temperature trend in Fig. 150.3 extends back to 1750 even though there appears to be no temperature data for Malta before 1850 (for a list of stations in Malta see here).

 

 Fig. 150.3: The temperature trend for Malta since 1750 according to Berkeley Earth.

 

If we compare the raw data for Luqa with the BE adjusted version we find that there is virtually no difference between the two (see Fig. 150.4 below). It is actually very unusual for such a long dataset not to undergo at least one breakpoint adjustment so this result is quite surprising.

 

Fig. 150.4: The 5-year average of the monthly mean temperature change for Luqa since 1820 based on the original raw data from Fig. 150.1 (in blue) and the Berkeley Earth adjusted data from Fig. 150.2 (in red).

 

As there is no data from Malta to compare the Luqa data against we could instead compare it with temperature data from the nearby Italian islands of Lampedusa (BE ID: 155869) and Pantelleria (BE ID: 175525 ). The locations of these islands relative to Malta and Sicily is shown in the map in Fig. 150.5 below. Lampedusa is about 150 km from both Malta and Pantelleria.


Fig. 150.5: The (approximate) locations of the weather stations in Malta (Luqa), Lampedusa and Pantelleria. Those stations denoted with squares are long stations with over 1200 months of data, while diamonds denote medium stations with more than 480 months of data.

 

Unfortunately the temperature data from Lampedusa and Pantelleria only start around 1960 but both sets show temperature rises after 1980 that are similar to that seen in the Luqa data. There is also good correlation in the high frequency (less than 12 months) fluctuations, but the medium timescale fluctuations with peak widths of more than 12 months are not well correlated.

 

Fig. 150.6: A comparison of the 5-year average temperature change for the islands of Malta, Lampedusa and Pantelleria since 1960.

 

The other data that we could compare Luqa with is that of Italy. This is shown in Fig. 150.7 below and here the medium timescale fluctuations in the two datasets correlate much better.

 

Fig. 150.7: A comparison of the 5-year average temperature change for Malta and Italy.

 

 

Summary

The temperature data for Malta clearly shows that the climate warmed by over 0.6°C after 1980 (see Fig. 150.1).

Before 1980 there is a large amount of natural variation in the temperature data but no overall upward trend.

The temperature trend for Malta can only be determined using one set of station data: Luqa (BE ID:156721). This makes it very unreliable. Comparing it with the neighbouring islands of Lampedusa and Pantelleria only confirms the temperature trend after 1960 (see Fig. 150.6).

There does appear to be a good correlation between the temperature trend of Luqa in Malta and that of Italy in Fig. 148.2 of Post 148 extending back as far as 1890 (see Fig. 150.7). This would suggest that the temperature trends of Malta and Italy have been very similar over at least the last 150 years.



Acronyms

BE = Berkeley Earth.

MRT = monthly reference temperature (see Post 47).

MTA = mean temperature anomaly.

Long station = a station with over 1200 months (100 years) of data before 2014.

Medium station = a station with over 480 months (40 years) of data before 2014.

List of all stations in Malta with links to their raw data files.