The island of Puerto Rico is located just over 100 km due east of the island of Hispaniola and about 800 km north of the Venezuelan coast. It is one of the larger islands in the Caribbean but it is slightly smaller than Jamaica and much smaller than both Cuba and Hispaniola. And yet it has by far the best temperature data in the region with eight long stations and over thirty medium stations (for a full list of stations see here) and data that extends back to 1898. This is probably because it has been a US territory since 1898.
The temperature trend for Puerto Rico was determined by averaging the individual temperature anomalies from each station to generate the mean temperature anomaly (MTA) each month. These are shown in Fig. 110.1 below. Overall the temperature trend is positive with a modest warming of about 0.3°C in the 80 years before 1990 followed by a larger temperature rise of 0.5°C over the next 15 years. This fits with the pattern we have seen in many other countries of temperature stability before 1980 and a sudden rise of 0.5°C thereafter. While this is concerning and demanding of explanation, it is a long way short of the values claimed globally by climate scientists and the IPCC for land-based temperature rises.
Fig. 110.1: The mean temperature change for Puerto Rico relative to the 1951-1980 monthly averages. The best fit is applied to the monthly mean data from 1911 to 1980 and has a positive gradient of +0.39 ± 0.09 °C per century.
The temperature anomalies for each station were determined using the usual method as outlined in Post 47. This involved first calculating the monthly reference temperatures (MRTs) for each station using a set reference period, in this case from 1951 to 1980, and then subtracting the MRTs from the raw temperature data to deliver the anomalies. If a station had at least twelve valid temperatures per month within the MRT interval then its anomalies were included in the calculation of the regional mean temperature anomaly (MTA). The total number of stations included in the MTA in Fig. 110.1 each month is indicated in Fig. 110.2 below. The peak in the frequency around 1965 suggests that the 1951-1980 interval was indeed the most appropriate.
Fig. 110.2: The number of station records included each month in the mean temperature anomaly (MTA) trend for Puerto Rico in Fig. 110.1.
The map in Fig. 110.3 below illustrates the geographical distribution of the stations in Puerto Rico. There are clearly more stations in the eastern half of the island than in the west, but in both halves the distribution is fairly even except for a greater clustering around San Juan. This means that a simple average of station anomalies should be reasonably accurate as previous posts have demonstrated.
Fig. 110.3: The (approximate) locations of the 41 longest weather station records in Puerto Rico. Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue. Those denoted with squares are long stations with over 1200 months of data, while diamonds denote medium stations with more than 480 months of data.
Next I calculate the corresponding MTA result based on data that has been adjusted by Berkeley Earth (BE). The result is shown in Fig. 110.4 below and, unlike the raw data in Fig. 110.1, it exhibits a continuous strong warming trend with temperatures rising by over 1.2°C since 1910 (see orange 10-year moving average curve). This is about 50% more than is seen in the raw data.
Fig. 110.4: Temperature trends for Puerto Rico based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1911-2010 and has a gradient of +1.13 ± 0.03°C/century.
Comparing the curves in Fig. 110.4 with the published Berkeley Earth (BE) version in Fig. 110.5 below indicates remarkably good agreement at least as far back as 1910. This indicates that the simple averaging of anomalies to generate the MTA in Fig. 110.1 is as effective and accurate as the more complex gridding method used by Berkeley Earth. It also means that the averaging process cannot be responsible for the large difference in trends between that using unadjusted data in Fig. 110.1 and that using adjusted data in Fig. 101.4.
Fig. 110.5: The temperature trend for Puerto Rico since 1820 according to Berkeley Earth.
The differences between the MTA in Fig. 110.1 and the BE versions using adjusted data in Fig. 110.4 and Fig. 110.5 are instead mainly due to the data processing procedures used by Berkeley Earth. These include homogenization, gridding, Kriging and most significantly breakpoint adjustments. These lead to changes to the original temperature data, the magnitude of these adjustments being the difference in the MTA values seen in Fig. 110.1 and Fig. 110.4. The magnitudes of these adjustments are shown graphically in Fig. 110.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 110.4) and unadjusted data (Fig. 110.1), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Both are considerable with the former leading to an additional warming since 1900 of up to 0.7°C.
Fig. 110.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 110.4 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 1911-2010 has a positive gradient of +0.471 ± 0.008 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
According to the raw unadjusted temperature data, over the past century the climate of Puerto Rico has warmed slowly before 1990 and then more rapidly thereafter (see Fig. 110.1). The total warming is likely to be about 0.8°C
Over the same period adjusted temperature data from Berkeley Earth claims to show that the climate of Puerto Rico has warmed by over 1.2°C (see Fig. 110.4 and Fig. 110.5).
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
List of all stations and their raw data files.
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