The Guianas is the region of north-eastern South America that comprises the three territories of Guyana (formerly British Guiana), Suriname (formerly Dutch Guiana) and French Guiana. It sits on the Atlantic coast between Venezuela and Brazil, and as the data in Fig. 113.1 below shows, it does not appear to have experienced any significant climate change over the last 100 years, although the mean temperature has fluctuated significantly by up to 1°C (see yellow curve).
Fig. 113.1: The mean temperature change for the Guianas relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1896 to 2005 and has a slight positive gradient of +0.11 ± 0.04 °C per century.
The MTA in Fig. 113.1 was calculated by averaging the temperature anomalies from the fourteen longest temperature records for the region. Eight of these records were from medium stations with over 480 months of temperature data before the end of 2013, but there are only two long stations with more than 1200 months of data.
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 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 MTA calculation. The total number of stations included in the MTA in Fig. 113.1 each month is indicated in Fig. 113.2 below. The peak just around 1975 suggests that the 1961-1990 interval was indeed the most appropriate.
Fig. 113.2: The number of station records included each month in the mean temperature anomaly (MTA) trend for the Guianas in Fig. 113.1.
The locations of the fourteen main stations are shown in the map in Fig. 113.3 below. This appears to show that the geographical spread is fairly uniform, although there does appear to be far more stations in Suriname than in either Guyana or French Guiana. This variation in station density is probably not sufficient to significantly distort the average in Fig. 113.1 from its true value though. In which case the simple average of the anomalies from all stations used to construct the MTA in Fig. 113.1 should still yield a fairly accurate temperature trend for the region as a whole.
Overall there are more stations close to the coast than inland, and the coastal stations appear more likely to have warming trends. A warming trend is defined here as one where the temperature gradient for 1911-2010 is positive and exceeds twice the uncertainty in that trend.
Fig. 113.3: The (approximate) locations of the fourteen longest weather station records in the Guianas. 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 stations with more than 300 months of data.
In contrast to Fig. 113.1, the corresponding MTA dataset based on data that has been adjusted by Berkeley Earth (BE) exhibits a strong warming trend with temperatures rising by over 1.5°C since 1890 (see Fig. 113.4 below).
Fig. 113.4: Temperature trends for the Guianas based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1896-2005 and has a gradient of +1.06 ± 0.03°C/century.
If we next compare the curves in Fig. 113.4 with the published Berkeley Earth (BE) version for Suriname in Fig. 113.5 below (where most stations are located) we see that there is remarkably good agreement between the two sets of data at least as far back as 1900. This indicates that the simple averaging of anomalies used to generate the BE MTA in Fig. 113.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 113.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 113.1.
Fig. 113.5: The temperature trend for Suriname since 1820 according to Berkeley Earth.
The differences between the MTA in Fig. 113.1 and the BE versions using adjusted data in Fig. 113.4 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. 113.1 and Fig. 113.4. The magnitudes of these adjustments are shown graphically in Fig. 113.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 113.4) and unadjusted data (Fig. 113.1), 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 1.6°C.
Fig. 113.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 113.4 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 1896-2005 has a positive gradient of +0.96 ± 0.03 °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 the Guianas has remained stable (see Fig. 113.1).
Over the same period adjusted temperature data from Berkeley Earth appears to show that the climate of the Guianas has warmed by as much as 1.6°C (see Fig. 113.4).
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
Link to list of all stations in Guyana and their raw data files.
Link to list of all stations in Suriname and their raw data files.
Link to list of all stations in French Guiana and their raw data files.
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