In this post I will study the extent of climate change in Central America. I have already discussed the trend for Mexico in the previous post where the conclusions were ambiguous. The warming that was seen in the mean temperature anomaly (MTA) could have been more than 1°C since 1900 (see Fig. 93.7), but could equally have been close to zero or even negative (see Fig. 93.6) depending on which partial dataset was used. The compromise was an estimate of about 0.6°C of warming (see Fig. 93.1).
But at least Mexico had over 130 significant temperature records on which to base these conclusions. The rest of Central America (Belize, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama) in contrast has less than forty. For this reason I have combined the analysis for these seven countries into a single post.
Fig. 94.1: The (approximate) locations of the weather stations in Central America. 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 stations with over 600 months of data, while diamonds denote stations with more than 360 months of data.
In total the seven countries being considered here have only 32 medium stations with over 480 months of data before 2013 (see here for a list) and none with more than 900 months of data, although there are 19 with over 600 months of data. There are an additional ten stations with over 360 months of data. The location of these stations are shown on the map in Fig. 94.1 above. It is immediately clear that there is far from an even distribution of these stations across the region with much of Guatemala, Nicaragua and Panama having little coverage.
The other complication is that the stations in the region do not all have data for the same time period. Only about five stations have a significant amount of temperature data before 1950 and none of these have any data after 1980, whereas about eleven stations have no data before 1970. That makes it difficult to combine both into a single trend because these two sets of stations require different 30-year reference time periods against which to measure the temperature change.
Fig. 94.2: The mean temperature change for Central America relative to the 1951-1980 monthly averages. The best fit is applied to the monthly mean data from 1921 to 1975 and has a positive gradient of +0.28 ± 0.11 °C per century.
One solution is to calculate different monthly reference temperatures (MRTs) for each set. This is what I have done in Fig. 94.2 above and Fig. 94.3 below. The results are broadly the same but have significant differences.
In Fig. 94.2 the MRTs were calculated for the 30-year period from 1951 to 1980. The temperature anomalies for each station were determined by calculating the twelve monthly reference temperatures (MRTs) for each station using the method described previously in Post 47. The MRTs for each station were then subtracted from that station's raw temperature data to produce the anomalies for that station. These were then averaged to obtain the mean temperature anomaly (MTA) for each month.
The results in Fig. 94.2 indicate that there was little or no temperature rise in the region before 1975, but a significant rise of about 1°C spread over the following twenty years. The mean temperature then seems to plateau for twenty years.
Fig. 94.3: The mean temperature change for Central America relative to the 1971-2000 monthly averages. The best fit is applied to the monthly mean data from 1917 to 1975 and has a negative gradient of -0.18 ± 0.11 °C per century.
A similar picture is seen for the data in Fig. 94.3 where the MRT period was defined to be from 1971 to 2000. The main differences are that the temperature trend before 1975 is now negative, and the temperature rise thereafter is slightly less, being about 0.8°C rather than about 1.2°C. So which of these two data interpretations are more likely to be correct? The answer depends on which graph has the better data.
Fig. 94.4: The number of station records included each month in the mean temperature anomaly (MTA) trend for Central America in Fig. 94.2 (blue curve) and Fig. 94.3 (red curve).
The graph in Fig. 94.4 above shows the number of stations used to determine the MTA each month for both Fig. 94.2 and Fig. 94.3. It indicates that Fig. 94.3 has the greater amount of data after 1975 but not before. This suggests that the temperature trend before 1975 resembled that in Fig. 94.2 and was therefore stable. After 1975 the temperature rose, but not by as much as Fig. 94.2 suggests. It probably rose by about 0.8°C in line with the data shown in Fig. 94.3.
Fig. 94.5: Temperature trends for Central America based on Berkeley Earth (BE) adjusted data. The average is for anomalies from all stations with over 240 months of data. The best fit linear trend line (in red) is for the period 1901-2010 and has a gradient of +0.83 ± 0.03°C/century.
Of course none of this corresponds to the trend produced by Berkeley Earth (BE), or even the trend that results from averaging the BE adjusted data. The latter is shown in Fig. 94.5 above. This graph is the result of averaging the anomaly data for each station after it has been adjusted using breakpoint alignment. As I have usually to be the case in previous country analyses, it differs markedly from the unadjusted data. It is also worth noting that the BE anomalies before breakpoint alignment already differ from anomalies derived solely from the raw station data because Berkeley Earth appears to use homogenization, Kriging and gridding in its process to determine the station anomalies. That is yet another reason for looking at the raw data instead.
What is apparent is that the trend shown in Fig. 94.5 above differs considerably from the official Berkeley Earth temperature trend for the region that I have reproduced in Fig. 94.6 below. That is because it the graph in Fig. 94.6 includes data from Mexico. In fact the curves in Fig. 94.6 are very similar to the equivalent graph for Mexico shown in Fig. 93.3 in Post 93. This is not surprising as the area of Mexico is four times the combined area of the seven countries being considered here.
Fig. 94.6: The temperature trend for the whole of Central America, including Mexico, since 1830 according to Berkeley Earth.
If we add the BE adjust data from Mexico (weighted 79% for its area) to the data in Fig. 94.5 the result is the graph shown in Fig. 94.7 below. As expected this agrees closely with Fig. 94.6 at least for data after 1920.
Fig. 94.7: Temperature trends for Central America including Mexico 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 +0.55 ± 0.02°C/century.
Summary and conclusions
1) There is no evidence of any meaningful rise in temperatures in Central America before 1975, even though the data is not great.
2) After 1975 the temperature appears to rise suddenly but gradually until 1995 and then plateau.
3) The maximum temperature rise after 1975 is about 1°C.
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
Link to list of all stations (including Mexico).
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