59. Paraguay - temperature trends COOLING

Paraguay has even less temperature data than Bolivia, but it does have some data from before 1900 and it does have one long station with over 1200 months of data (Asuncion Aeropuerto - Berkeley Earth ID: 157448). Despite this lack of data there is still a clear trend in the data that we do have, and that trend is negative. There has been no global warming in Paraguay either in the last 100 years.

 

Fig. 59.1: The temperature trend for Paraguay since 1893. The best fit is applied to the interval 1933-2012 and has a negative gradient of -1.78 ± 0.21 °C per century. The monthly temperature changes are defined relative to the 1981-2010 monthly averages.

 

The temperature trend in Fig. 59.1 above was derived by averaging the temperature anomalies from all the medium stations with more than 480 months of data together with the single long station. This amounted to only thirteen stations in total (for a list see here) all of which had at least twelve years of data within the interval of 1981-2010 that was used to determine the monthly reference temperatures (MRTs). The use of MRTs is explained in Post 47.

The trend in Fig. 59.1 is clearly strongly negative from about 1940 onwards. This corresponds to the period with the greatest number of active stations, as shown in Fig. 59.2 below, with more than ten sets of station data being available for most months between 1950 and 2013. This confers a high degree of confidence to the trend in Fig. 59.1 as I illustrated in Post 57 previously. In contrast, the trend before 1940 is much less reliable as it is based on the fragmented data from a single station: Asuncion Aeropuerto (Berkeley Earth ID: 157448). For this reason the best fit trend line in Fig. 59.1 is only calculated using the eighty years of data after 1933.

 

Fig. 59.2: The number of station records included each month in the mean temperature trend for Paraguay when the MRT interval is 1981-2010.

 

The geographical distribution of the long and medium stations in Paraguay is illustrated in Fig. 59.3 below. These are classed as either warming stations (in red) or stable/cooling stations in blue. The criteria for determining if a station is warming are two-fold. Firstly, the temperature trend must exceed twice the error in the trend in order to be statistically significant. Secondly, the overall temperature rise must exceed 0.25 °C in order for it to exceed the threshold below which it could be considered as merely a random fluctuation in the data. As I pointed out previously, this threshold may be on the low side as natural fluctuations in the long-term temperature trend may be much greater than 0.25°C. In fact in some cases they may exceed 1°C.

 

Fig. 59.3: The locations of long stations (large squares) and medium stations (small diamonds) in Paraguay. Those stations with a high warming trend are marked in red. Those with cooling or stable trends are marked in blue.

 

It is clear from Fig. 59.3 that there is a good, even spread of stations in the east of Paraguay with very little clustering of stations other than near the capital Asuncion and in the middle of the country near Concepcion. However, there is very little coverage in the north-west. Nevertheless, overall this suggests that the simple averaging approach employed here to determine the regional temperature trend is still appropriate and is likely to give results that are close to the true result as will be shown below. What is also apparent is the almost complete lack of warming. Only two of the thirteen stations exhibit any significant warming.

 

 

Fig. 59.4: Temperature trend in Paraguay since 1893 derived by aggregating and averaging the Berkeley Earth adjusted data for all medium stations. The best fit linear trend line (in red) is for the period 1934-2012 and has a gradient of +1.01 ± 0.07 °C/century.

This hypothesis is confirmed by comparing the regional trend using Berkeley Earth adjusted data in Fig. 59.4 above, and which was also constructed using a simple averaging method, with that published by Berkeley Earth and shown in Fig. 59.5 below. This comparison shows that a simple average of the adjusted data from the Berkeley Earth data files gives the same result for the regional trend in Paraguay as the Berkeley Earth version, even though Berkeley Earth appears to use weighted averages for its regional averaging. This in turn also suggests that weighted averaging is not necessary in Paraguay.

 

Fig. 59.5: The temperature trend for Paraguay since 1830 according to Berkeley Earth.

What is also apparent is that there is a clear difference between the temperature trend produced by Berkeley Earth in Fig. 59.5 and that which can be derived from the original data in Fig. 59.1, not only in the magnitudes of the two different temperature trends, but also in their directions. The total difference is illustrated in Fig. 59.6 below and amounts to an additional 2.7°C per century of warming that has been added to a regional trend that has actually been cooling at -1.78°C per century since 1940. That is over 2°C in total. What is more, most of these temperature adjustments are due to the very breakpoint adjustments that I demonstrated in Post 57 were unnecessary.

 

 

Fig. 59.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 59.4 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 1934-2012 has a positive gradient of +2.70 ± 0.08 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

 

Conclusion

The results here indicate that there has been no global warming in Paraguay in the last 100 years. The regional temperature is either stable or cooling, as shown in Fig. 59.1.

 

Addendum

 

Fig. 59.7: The temperature trend for Paraguay since 1893 including short stations with over 300 months of data. The best fit is applied to the interval 1933-2012 and has a negative gradient of -1.64 ± 0.22 °C per century. The monthly temperature changes are defined relative to the 1981-2010 monthly averages.

 

There are only thirteen long and medium stations in Paraguay. However, there are another five with over 300 months of data. Including these could improve slightly the accuracy of the trend after 1980 where most of the new data exists. This is shown in Fig. 59.7 above. The trend in Fig. 59.7 is very similar to that shown in Fig. 59.1, with only a slight increase in the overall trend.