There are thirteen medium stations with over 480 months of data in the Central African Republic (CAR), but only one station has over 800 months of data before 2014, and none have any data before 1940 (see here for a full list). In addition, there are another two stations with over 300 months of data.
The neighbouring countries of Chad, Cameroon, Congo and the DRC (formerly Zaire) have virtually no data before 1940 either. Only Sudan has significant data pre-1940. This means it is not possible to know the true temperature trend of CAR before 1940. What the data that we do have tells us is that the climate of the Central African Republic cooled by over 0.5°C from 1950 onwards (see Fig. 116.1 below).
Fig. 116.1: The mean temperature change for the Central African Republic relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1941 to 2005 and has a negative gradient of -0.50 ± 0.11 °C per century.
In order to quantify the changes to the climate of the CAR since 1940 the temperature anomalies for each of the fifteen stations with the most data were determined and averaged. This was done using the usual method as outlined in Post 47 and involved first calculating the temperature anomaly each month for each station, and then averaging those anomalies to determine the mean temperature anomaly (MTA) for the country. This MTA is shown as a time series in Fig. 116.1 above and clearly shows that temperatures declined continuously from 1940.
The process of determining the MTA in Fig. 116.1 involved first determining the monthly reference temperatures (MRTs) for each station using a set reference period, in this case from 1961 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 calculation of the mean temperature anomaly (MTA). The total number of stations included in the MTA in Fig. 116.1 each month is indicated in Fig. 116.2 below. The peak in the frequency between 1960 and 1990 suggests that the 1961-1990 interval was indeed the most appropriate to use for the MRTs.
Fig. 116.2: The number of station records included each month in the mean temperature anomaly (MTA) trend for the Central African Republic in Fig. 116.1.
The locations of the fifteen stations with the most temperature data are shown in the map in Fig. 116.3 below. This appears to show that the geographical spread is fairly uniform, although there does appear to be more stations in the south of the country than in the north. This variation in station density is probably not sufficient to significantly distort the average in Fig. 116.1 from its true value though. In which case the simple average of the anomalies from all stations used to construct the MTA in Fig. 116.1 should still yield a fairly accurate temperature trend for the country as a whole.
Fig. 116.3: The (approximate) locations of the fifteen longest weather station records in the Central African Republic. 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 medium stations with over 480 months of data, while diamonds denote stations with more than 250 months of data.
If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 116.4 below. This again was determined by averaging each monthly anomaly from the fifteen longest stations and suggests that the climate was fairly stable before 1980 but then warmed by about 0.75°C thereafter.
Fig. 116.4: Temperature trends for the Central African Republic based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1941-2010 and has a positive gradient of +0.83 ± 0.08°C/century.
If we next compare the curves in Fig. 116.4 with the published Berkeley Earth (BE) version for the CAR in Fig. 116.5 below we see that there is good agreement between the two sets of data after 1940. This indicates that the simple averaging of anomalies used to generate the BE MTA in Fig. 116.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 116.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 116.1. What is more difficult to explain is how Berkeley Earth have determined the climate for the CAR as far back as 1880 when there is virtually no reliable temperature data for the country before 1940.
Fig. 116.5: The temperature trend for the Central African Republic since 1850 according to Berkeley Earth.
The differences between the MTA in Fig. 116.1 and the BE version using adjusted data in Fig. 116.4 are probably 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. 116.1 and Fig. 116.4. The magnitudes of these adjustments are shown graphically in Fig. 116.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 116.4) and unadjusted data (Fig. 116.1), 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 1940 of up to 1.5°C.
Fig. 116.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 116.4 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 1941-2010 has a positive gradient of +1.32 ± 0.03 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
According to the raw unadjusted temperature data, the climate of the CAR has cooled from 1940 by about 0.5°C (see Fig. 116.1).
Over the same period adjusted temperature data from Berkeley Earth appears to show that the climate of the CAR has warmed by over 0.5°C (see Fig. 116.5).
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
Link to list of all stations in the Central African Republic and their raw data files.
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