The biggest problem with assessing climate change in Bolivia is the relative lack of data. There is no data from before 1900 and no long stations with over 1200 months of data. Despite this there is a clear trend in the data that we do have, and that trend is negative. There has been no global warming in Bolivia in the last 100 years.
Fig. 58.1: The temperature trend for Bolivia since 1910. The best fit is applied to the interval 1953-2012 and has a negative gradient of -0.16 ± 0.17 °C per century. The monthly temperature changes are defined relative to the 1981-2010 monthly averages.
The temperature trend in Fig. 58.1 above was derived by averaging the temperature anomalies from all the medium stations with more than 480 months of data. This amounted to 25 stations in total (for a list see here). However, one station at La Paz (Berkeley Earth ID: 5644) was excluded because it had no 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. 58.1 is clearly negative from about 1950 onwards. This corresponds to the period with the greatest number of active stations, as shown in Fig. 58.2 below, with more than 20 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. 58.1 as I illustrated in Post 57 previously. In contrast, the trend before 1950 is much less reliable. For this reason the best fit trend line in Fig. 58.1 is only calculated using the sixty years of data after 1953.
Fig. 58.2: The number of station records included each month in the mean temperature trend for Bolivia when the MRT interval is 1981-2010.
The geographical distribution of the medium stations in Bolivia is illustrated in Fig. 58.3 below. These are classed as either warming stations (in red) or stable/cooling stations in blue, and there appears to be a fairly even split between the two groups. 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 sound. Secondly, the overall temperature rise must exceed 0.25 °C in order for it to exceed the threshold for it to be regarded as merely a random fluctuation in the data. I should point out that even 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.
Fig. 58.3: The locations of the medium stations (small diamonds) in Bolivia. 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. 58.3 that there is a good, even spread of stations in Bolivia with very little clustering of stations other than near the capital La Paz. The only area of Bolivia with sparse coverage is the mountainous Andes region in the south-west. This suggests that the simple averaging approach employed here to determine the regional temperature trend is highly appropriate and is likely to give results that are close to the true result.
Fig. 58.4: Temperature trend in Bolivia since 1910 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 1914-2012 and has a gradient of +0.66 ± 0.04 °C/century.
This hypothesis is confirmed by the regional trend in Fig. 58.4 above which was also constructed using a simple averaging method, and which is virtually identical to the trend published by Berkeley Earth and shown in Fig. 58.5 below. This shows that a simple average of the adjusted data from the Berkeley Earth data files gives the same result for the regional trend in Bolivia 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, except possibly in cases of extreme clustering of stations in urban areas, of which there is none in Bolivia.
Fig. 58.5: The temperature trend for Bolivia since 1850 according to Berkeley Earth.
What is apparent is that there is a clear difference between the temperature trend produced by Berkeley Earth in Fig. 58.5 and that which can be derived from the original data in Fig. 58.1, not only in the magnitudes of the two different temperature trends, but also in their directions. The total difference is illustrated in Fig. 58.6 below and amounts to an additional 0.72°C per century of warming that has been added to a regional trend that is actually cooling at -0.16°C per century. What is more, most of these temperature adjustments are due to the very breakpoint adjustments that I demonstrated in my last post were unnecessary.
Fig. 58.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 58.4 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 1914-2012 has a positive gradient of +0.72 ± 0.07 °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 Bolivia in the last 100 years. The regional temperature is either stable or cooling, as shown in Fig. 58.1.
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