Over the previous five posts I have examined the temperature records of the larger islands in the Caribbean that are found in the archipelago known as the Greater Antilles. In this post I will concentrate on the remaining islands of the Caribbean in the Lesser Antilles.
The Lesser Antilles comprises all the islands of the Caribbean between the coast of Venezuela to the south and Puerto Rico to the north. These in turn are subdivided into three distinct smaller archipelagos: the Leeward Islands, the Windward Islands, and the Leeward Antilles (see Fig. 111.1 below).
Fig. 111.1: A map of the Caribbean Sea showing the location of the Lesser Antilles.
Most of the main islands of the Lesser Antilles have at least one weather station as illustrated in Fig. 111.2 below. However none are long stations with over 1200 months of data before 2014, although seven stations (Le Raizet, Lamentin, Codrington, Richmond Hill, Pearls Airport, St. Clair Experimental Station and St. Clair Ex) do have data from before 1900 (for a list of Caribbean stations see here). Unfortunately most of the data for these seven stations is significantly fragmented, and as a result the temperature anomalies fluctuate massively over time, particularly before 1940. The most prominent stations are shown in Fig. 111.2 and all have over 400 months of data before 2014.
Fig. 111.2: The (approximate) locations of the weather stations in the Lesser Antilles with over 400 months of data. 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.
As the stations shown in Fig. 111.2 appear well separated geographically we can as a first approximation average their individual temperature anomalies to determine the mean temperature anomaly (MTA) for each month for the region as a whole. These monthly MTAs are shown in Fig. 111.3 below.
Fig. 111.3: The mean temperature change for the Lesser Antilles relative to the 1931-1990 monthly averages. The best fit is applied to the monthly mean data from 1941 to 1980 and has a slight positive gradient of +0.29 ± 0.14 °C per century.
The 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 1931 to 1990, 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 MTA calculation.
The MRT interval used here is twice as long as normal due to the wide distribution of data between different stations. As mentioned above, seven stations have data before 1900 but most of these have no data after 1960. In contrast most stations with data after 1970 have none before 1960. So the only way to include both sets is to widen the MRT interval. This will introduce some degree of error but that error will be limited to at most to a value equivalent to the rise in temperature across the MRT period. The data in Fig. 111.3 suggests that this is relatively small. The result is that a total of 25 stations were then included in the MTA calculation with the number each month indicated in Fig. 111.4 below. The station at St. Clair Ex was excluded due to a lack of data within the MRT interval.
The MTA in Fig. 111.3 has three distinct parts. Between 1940 and 1980 the trend is neutral as indicated by the best fit line in red. After 1980 there is significant warming of about 0.5°C. Before 1940 the picture is difficult to discern as there are fewer stations with data contributing to the MTA (see Fig. 111.4 below) and most of these stations have data that is discontinuous and highly erratic. In contrast, the MTA trend after 1940 is likely to be much more reliable as it is constructed using up to twenty different sets of station data most of which are continuous.
Fig. 111.4: The number of station records included each month in the mean temperature anomaly (MTA) trend for the Lesser Antilles in Fig. 111.3.
Next I calculate the corresponding MTA result based on data that has been adjusted by Berkeley Earth (BE). The result is shown in Fig. 111.5 below and, unlike the raw data in Fig. 111.3, it exhibits a strong continuous warming trend with temperatures rising by over 1.4°C since 1910 (see orange curve). This is about the same as is seen in the raw data. However if we just look at the period since 1930 where the data is more plentiful due to there being more active stations we see that the rise is temperature is about 1.0°C. This is 0.5°C more than is seen in the raw data in Fig. 111.3.
Fig. 111.5: Temperature trends for the Lesser Antilles 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 +1.19 ± 0.02°C/century.
The differences between the MTA in Fig. 111.3 and the BE version using adjusted data in Fig. 111.5 are 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. 111.3 and Fig. 111.5. The magnitudes of these adjustments are shown graphically in Fig. 111.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 111.5) and unadjusted data (Fig. 111.3), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. From 1920 onwards both are similar in magnitude and lead to an additional warming since 1940 of about 0.5°C.
Fig. 111.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 111.5 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 1921-1980 has a positive gradient of +0.289 ± 0.019 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
According to the raw unadjusted temperature data, over the forty year period up to 1980 the climate of the Lesser Antilles remained fairly stable before experiencing a rapid increase in temperature of about 0.5°C (see Fig. 111.3).
The data before 1940 is too fragmented and erratic to divulge a definitive trend.
Over the period 1901-2010 the adjusted temperature data from Berkeley Earth claims to show that the climate of the Lesser Antilles has warmed by as much as 1.5°C (see Fig. 111.5).
These adjustments appear to have added around 0.5°C of warming since 1940 (see Fig. 111.6).
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
List of all stations with data before 1900
Le Raizet (Guadeloupe)
Lamentin (Martinique)
Codrington (Barbados)
Richmond Hill (Grenada)
Pearls Airport (Grenada)
St. Clair Experimental Station (Trinidad and Tobago)
St. Clair Ex (Trinidad and Tobago)
