60. Uruguay - temperature trends WARMING 0.4°C to 1°C

Like Paraguay, Uruguay 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 (Montevideo/Prado - Berkeley Earth ID: 165708). In addition there are ten medium stations with over 480 months of data and another eight with over 180 months of data.

 

Fig. 60.1: The temperature trend for Uruguay since 1880. The best fit is applied to the interval 1933-2012 and has a positive gradient of +0.96 ± 0.13 °C per century. The monthly temperature changes are defined relative to the 1981-2010 monthly averages.

 

The temperature trend in Fig. 60.1 above was derived by averaging the temperature anomalies from all the stations with more than 180 months of data. This amounted to only nineteen 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. 60.1 is clearly strongly positive but there is only one significant set of station data before 1950, and only about ten between 1950 and 1980 (see Fig. 60.2 below). This means that we can only have a high degree of confidence in the trend shown in Fig. 60.1 after 1950, as I explained in Post 57 previously. So while it is possible that Uruguay has warmed at the same rate since 1880, it is also possible that the only significant temperature rise has occurred after 1970. If so, this would amount to a total warming of only about 0.4°C.

 

Fig. 60.2: The number of station records included each month in the mean temperature trend for Uruguay when the MRT interval is 1981-2010.

The geographical distribution of the long and medium stations in Uruguay is illustrated in Fig. 60.3 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 as the 5-year moving average in Fig. 60.1 appears to indicate. 

 

Fig. 60.3: The locations of long stations (large squares) and medium stations (small diamonds) in Uruguay. Those stations with a high warming trend are marked in red. Those with cooling or stable trends are marked in blue.

 

Clearly Fig. 60.3 shows that the majority of stations in Uruguay have warmed over their history. Out of the eleven long and medium stations, only three are stable or cooling. It is also clear from Fig. 60.3 that there is a good, even spread of those stations around Uruguay with very little clustering of stations other than near the capital Montevideo. This suggests that the simple averaging approach employed here to determine the regional temperature trend in Fig. 60.1 is appropriate and highly likely to give results that are very close to the true result. Evidence for this is shown below.

 

Fig. 60.4: Temperature trend in Uruguay since 1880 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 1901-2010 and has a gradient of +1.00 ± 0.04 °C/century.

 

This hypothesis that a simple averaging process is sufficient to determine the regional trend is confirmed by comparing the regional trend in Fig. 60.4 above, which was calculated using Berkeley Earth adjusted data and a simple averaging method, with that published by Berkeley Earth and shown in Fig. 60.5 below. This comparison shows that a simple average of the adjusted data from the Berkeley Earth data files (Fig. 60.4) gives the same result for the regional trend in Uruguay as the Berkeley Earth version (Fig. 60.5), 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 Uruguay.

 

Fig. 60.5: The temperature trend for Uruguay since 1830 according to Berkeley Earth.

What is also apparent is that there some distinct differences between the temperature trend produced by Berkeley Earth in Fig. 60.5 and that which can be derived from the original data in Fig. 60.1. The total difference is illustrated in Fig. 60.6 below and amounts to an additional 0.11°C per century of warming overall. This additional warming is greatest between 1950 and 2000, but it appears that the result of many of the biggest adjustments is to smooth the trend curve rather than to add additional warming. However, as I demonstrated in Post 57 previously, most of these temperature adjustments are unnecessary.

 

Fig. 60.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 60.4 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 1901-2010 has a positive gradient of +0.11 ± 0.08 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

 

Conclusion

The results here indicate that global warming in Uruguay has probably been modest (about 0.4°C) and may have only occurred in the 1970s. Without more early data from before 1950 it is difficult to tell for certain.