Indonesia is one of the largest countries in the world and has one of the largest populations at over 267 million. Its archipelago of islands straddles the equator and stretches from a longitude of 95°E to 141°E, a distance of over 5000 km. The country has 53 medium length temperature records with between 480 and 1200 months of data, but only one long station record with more than 1200 months of data (see here). That station is Jakarta Observatorium (Berkeley Earth ID: 155660). It is also the station with the most pronounced warming trend (see Fig. 31.1 below).
Fig. 31.1: The temperature trend for Jakarta Obervatorium since 1866. The best fit is applied to the interval 1866-2013 and has a gradient of 1.82 ± 0.08 °C per century. The temperature changes are relative to the 1961-1990 average.
Overall the temperature rise for Jakarta Obseratorium is nearly 2.7 °C from 1866 to 2013, yet this is not representative of the country as a whole. The medium stations in Indonesia exhibit both warming and stable trends as shown in Fig. 31.2 below. In this case stable trends are defined to be those with a warming that is less than twice the uncertainty. The stations are also fairly evenly dispersed, but are mainly coastal.
Fig. 31.2: The locations of long stations (large squares) and medium stations (small diamonds) in Indonesia. Those stations with a high warming trend are marked in red.
If we average all the records from the long and medium stations we get the overall trend shown in Fig. 31.3 below. Instantly we see a problem. While the overall trend since 1908 appears to be negative (-0.03 ± 0.04 °C per century in fact), there are large discontinuities around 1860, 1902 and 1941.
Fig. 31.3: The temperature trend for Indonesia since 1840. The best fit is applied to the interval 1908-2002 and has a negative gradient of -0.03 ± 0.04 °C per century. The temperature changes are relative to the 1961-1990 average.
The reason for this is the low number of station records before 1950, as illustrated in Fig. 31.4 below. For example, between 1866 and 1903 there is only one temperature record available, that of Jakarta Observatorium illustrated in Fig. 31.1 above.
Fig. 31.4: Number of stations per month included in the regional average for the Indonesia temperature anomaly. Only stations with more than 240 months of data in total and sufficient data in the period 1961-1990 are counted.
That is not the only problem, though. Low station numbers means that the average can be heavily distorted by one or two rogue datasets, and in this case there are at least three potential candidates in addition to Jakarta Obseratorium in Fig. 31.1. They are shown in the three figures below.
Fig. 31.5: The temperature trend for Christmas Island (Berkeley Earth ID: 154345) since 1900.
Fig. 31.6: The temperature trend for Padang (Berkeley Earth ID: 155706) since 1850.
Fig. 31.7: The temperature trend for Jakarta (Berkeley Earth ID: 15412) since 1866.
The last of these (Fig. 31.7) is another temperature record from Jakarta. Although this has none of the large temperature offsets seen in Fig. 31.5 and Fig. 31.6, it does appear to be as anomalous as the Jakarta Observatorium data in that it is inconsistent with the rest of the data for the country. It is also in close proximity to an existing station (Jakarta Observatorium). So, on the one hand it can corroborate the trend from Jakarta Observatorium, but on the other hand the weightings of both in the overall average trend should be halved.
The remaining question is whether the large temperature falls seen after 1950 in Fig. 31.5 and Fig. 31.6 are real. The suspicion (and it is just a suspicion) is that they are real because similar falls occur in too many other records. For example, they can also be seen in records from Dilli, Bandung and Pontianak.
So, rather than discarding the data from Christmas Island (Fig. 31.5) and Padang (Fig. 31.6), what happens if we discard both the datasets from Jakarta (Fig. 31.1 and Fig. 31.7) instead? The result is the trend shown in Fig. 31.8 above. This has a negative trend of -0.08 ± 0.04 °C per century, a trend which is also consistent with the data around 1850. The only anomaly is the data from 1903-1913 that is solely from Christmas Island.
The conclusion from this is that the only part of Indonesia that has exhibited any significant warming since 1850 is the capital and largest city, Jakarta. The rest of the country has seen no temperature rise at all.
Fig. 31.9: Temperature trend for all long and medium stations in Indonesiasince 1850 derived using the Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1871-2010 and has a gradient of +0.94 ± 0.03 °C/century.
What we need to do next is compare the results illustrated above, derived using the anomalies from the raw temperature data, with the equivalent results from Berkeley Earth. Summing and averaging the adjusted anomalies from Berkeley Earth yields the graph in Fig. 31.9 above. These are very similar to the published curves from Berkeley Earth shown in Fig. 31.10 below. Most of the differences are likely due to the inclusion of additional of smaller datasets in the Berkeley Earth plots.
The gradient of the best fit in Fig. 31.9 is +0.94 ± 0.03 °C per century. This is about half that seen in the data for Jakarta Observatorium shown in Fig. 31.1 above, but completely at odds with the data for the rest of the country shown in Fig. 31.8. It suggests that the temperature data from Jakarta has been assigned a greater level of significance (or weighting) and confidence than data from elsewhere in Indonesia. This is perhaps not surprising. The two records from Jakarta are two of the longest and most complete. They also exhibit trends that are both smooth and monotonic. But that does not mean their greater weighting is justified.
Fig. 31.10: Temperature trend for Indonesia since 1840 according to Berkeley Earth.
If we compare the Berkeley Earth adjusted data shown in Fig. 31.9 with the original raw unadjusted anomalies shown in Fig. 31.3, the difference is significant. This difference is shown in Fig. 31.11 below.
Fig. 31.11: The contribution of Berkeley Earth (BE) adjustments to the anomaly data after smoothing with a 12-month moving average. The linear best fit to the data is for the period 1904-2012 (red line) and the gradient is +0.96 ± 0.03 °C per century. The orange curve represents the contribution made to the BE adjustment curve by breakpoint adjustments only.
The data in Fig. 31.11 is shocking. If my analysis is correct, then it suggests that the adjustments made to the data by Berkeley Earth could have added about 0.95 °C to the warming trend since 1904. In other words, virtually all the warming claimed by Berkeley Earth to have occurred in Indonesia since 1904, and depicted in Fig. 31.10, may be the result of their own data adjustments, and not the original data. Moreover, most of this added warming appears to come from breakpoint adjustments.
Conclusions
1) The only warming seen in Indonesia appears to have occurred in Jakarta (see Fig. 31.1).
2) This warming has been large (about 2.7 °C) and continuous since 1866, which is consistent with its source being population growth linked to increased energy consumption and direct anthropogenic surface heating (DASH), as discussed in Post 14 and Post 29. It may also be a consequence of the urban heat island (UHI) effect.
3) There has been no warming of the overall climate in Indonesia since 1900 (see Fig. 31.8 below).
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