75. Southern Asia - overall temperature trend STABLE to 1975

In my previous four blog posts I determined the temperature trends for India, Pakistan, Sri Lanka and Bangladesh using unadjusted temperature data. The number of stations used to calculate the mean temperature each month is shown in Fig. 75.1 below. In the first three cases no warming was detectable before 1975, and only a modest temperature increase of about 0.6°C thereafter. In the case of Bangladesh there was a continuous warming that amounted to less than 0.3°C. This is significantly different from the conventional narrative on global warming, and highlights the impact that temperature adjustments have on the warming trends published by most of the main climate groups. In almost all cases the affect of these adjustments is to increase the rate of warming in the final trend as most of the regional trends I have published on this blog have also illustrated. In this post I will combine the results for India, Pakistan, Sri Lanka and Bangladesh into a temperature trend for the region.

Fig. 75.1: The number of station records included each month in the mean temperature anomaly for each of four countries in South Asia.

In Post 70 I performed a similar task for data from the different countries in South-East Asia using two separate methods. One method just involved a simple average of temperature anomalies from all the different stations in the region, while the second used a weighting process that was used to average the mean anomalies for the different countries based on their land areas. If all the countries have similar densities of stations, then both methods should yield the same result. In the case of South-East Asia that was broadly the case for most countries other than Burma, but the differences in the two methods still led to a difference in the temperature trend gradients of almost 0.1°C per century. In the case of South Asia there are large differences in station density between countries, and these differences can also change over time, as shown in Fig. 75.2 below. For this reason, in this post I have chosen to adopt the area weighted method to determine the regional temperature trend.

Fig. 75.2: The station density each month for each of four countries in South Asia.

By comparing Fig. 75.1 and Fig. 75.2 it can be seen that India clearly has the most sets of station data, but it is Sri Lanka that has the highest density of stations. However, the temperature anomaly for Sri Lanka will also be subject to greater uncertainty as it is based on only a handful of stations (eleven at most). Then again, the contribution of the Sri Lanka stations to the final regional trend will be small due to the much smaller area of Sri Lanka compared to both India and Pakistan.

Fig. 75.3: The temperature trend for South Asia based on an average of anomalies from all long and medium stations. The best fit is applied to the monthly mean data from 1876 to 1975 and has a positive gradient of +0.19 ± 0.06 °C per century. The monthly temperature changes are defined relative to the 1951-1980 monthly averages.

Applying an area weighted approach to the calculation results in the temperature anomaly time series shown in Fig. 75.3 above. This is calculated by multiplying the mean anomaly data for each country (e.g. the monthly data in Fig. 74.2 for Bangladesh) by the area of that country, and then summing the resulting products for all four countries in the region. Then the result is divided by the total area of the four countries.

Like the equivalent anomaly time series for the individual countries, the regional anomaly exhibits very little warming before 1975 with about 0.5°C of warming occurring thereafter (see Fig. 75.3). To reiterate, this is the result that we get when we use the actual raw unadjusted temperature data for each station and not the adjusted/homogenized data that is generally favoured by climate scientists.

Fig. 75.4: Temperature trends for South Asia based on an average of Berkeley Earth adjusted data from all long and medium stations. The best fit linear trend line (in red) is for the period 1876-2005 and has a gradient of +0.66 ± 0.02°C/century.

If, however, we perform the same calculation with adjusted data (which is available in the same data file as the unadjusted data on the Berkeley Earth site) we get a quite different result as is shown in Fig. 75.4 above. There is now a strong and continuous warming trend from 1875 onwards. The total warming is claimed to be 1.25°C, with 0.5°C of this occurring before 1975 (see 10-year average in Fig. 75.4). This is still less than that claimed by Berkeley Earth and shown in Fig. 75.5 below. However, this is likely to be because Berkeley Earth included both Iran and Afghanistan in the Southern Asia region, and according to Berkeley Earth the regional temperature trends for both Iran and Afghanistan exhibit over 1.5°C of warming after 1970. That would help to explain the larger temperature rise post-1970 seen in Fig. 75.5 (almost 1°C) than is seen in Fig. 75.4 (only 0.7°C). What is harder to explain is why there is so much warming before 1900 in Fig. 75.5 when there is a) so little data with almost all being due to one or two stations in India, and b) very little increase in atmospheric carbon dioxide levels to cause such a temperature increase.

Fig. 75.5: The temperature trend for South Asia since 1790 according to Berkeley Earth.

Finally, if we compare the temperature trends for the four countries of South Asia we see that while there are broad similarities in their general trends over timescales of decades, there is only moderate correlation of more short term features and fluctuations (see fig. 75.6 below). The main reason for this is distance. The principal cities of Bangladesh (Dhaka), Sri Lanka (Colombo) and Pakistan (Karachi) are all at least 2000 km apart. As I demonstrated in Post 11, temperature anomaly time series from stations that are more than 1500 km apart are very poorly correlated as Fig. 11.2(a) in that post illustrates.

Fig. 75.6: A comparison of the temperature trends of Bangladesh, Pakistan and Sri Lanka with that of neighbour India. For clarity the trends for Pakistan and Bangladesh are offset by +1°C and -1°C respectively.

Summary

The temperature trend for Southern Asia shows no warming before 1975 and only about 0.5°C thereafter (see Fig. 75.3).

The trend based on Berkeley Earth adjusted data shows significantly more warming (about 1.1°C in total), including significant warming (about 0.5°C) before 1975 (see Fig. 75.4).

72. Pakistan - temperature trends COOLING before 1997

There are 34 temperature records for Pakistan which have more than 480 months of data (see here for a complete list), of which five are long station records with over 1200 months of data. This means that its overall station density (stations per square kilometre) is about 30% higher than that of India, but it has less than half the density of long stations.

Fig. 72.1: The (approximate) locations of the long and medium temperature records in Pakistan. Those stations with a high warming trend between 1938 and 1997 are marked in red while those with cooling or stable trends are marked in blue. Those denoted with squares are long stations with over 1200 months of data.

The locations of the 34 long and medium stations are shown in Fig. 72.1 above. Their geographical spread is fairly even which suggests any simple average of their temperature anomalies should yield a fairly accurate approximation to the true mean temperature anomaly for the region. It can also be seen that the vast majority of stations (27) have stable or cooling trends for the 60 years up to 1997. 

The monthly temperature anomalies for each station were calculated by subtracting the monthly reference temperature (MRT) for the relevant month from the unadjusted mean temperature for that month. The MRTs are different and specific to each station, but were always calculated using data from the same time period of 1951-1980 for each station using the method described previously in Post 47. This ensures that the baseline reference temperature for each station is consistent so that all temperature changes over time are measured relative to the same point in time.

Fig. 72.2: The temperature trend for Pakistan based on an average of anomalies from all long and medium stations. The best fit is applied to the monthly mean data from 1938 to 1997 and has a negative gradient of -0.12 ± 0.21 °C per century. The monthly temperature changes are defined relative to the 1951-1980 monthly averages.

If we calculate the monthly temperature anomalies for the 34 stations in Fig. 72.1 and average them, the resulting times series exhibits a trend that is slightly warming, as shown in Fig. 72.2 above. However, all this warming occurs either before 1938 or after 1997. Between 1938 and 1997 the climate actually cools, and as Fig. 72.3 below indicates, the data for this time interval is probably more reliable as it is based on good data from a larger number of stations (between 20 and 34). The trend before 1931 is based on at most data from seven stations, most of which are located near major cities. On the other hand, significant data after 1990 comes from stations with large gaps in their temperature records between 1980 and 2000. 

The overall picture from the data in Fig. 72.2 is that, for most of the 20th century, the climate in Pakistan was stable or cooling. Any warming before 1930 was probably restricted to the large cities and was not indicative of the overall climate of the region. The only significant warming to have occurred in Pakistan in the last 150 years has occurred after 1997 and amounts to 0.65°C in total at most. Even then, its reliability is questionable due to the large gaps in much of the data that precede the temperature rise. This is why there is a large dip between 1975 and 2000 in the station frequency plot in Fig. 72.3 below.

Fig. 72.3: The number of station records included each month in the mean temperature trend for Pakistan in Fig. 72.2.

Of course this general temperature stability and moderate temperature rise after 1999 is not what is claimed by climate scientists. Below in Fig. 72.4 is the trend for Pakistan according to Berkeley Earth which shows a warming of at least 1.5°C since 1930. Clearly this is at odds with the trend based on the raw data in Fig. 72.2, and the reasons for the differences are not hard to find, or are unique to Pakistan. Similar differences have been highlighted in many of my previous posts. They are mainly due to the adjustments made to the original raw data by Berkeley Earth through the use of breakpoints and homogenization.

Fig. 72.4: The temperature trend for Pakistan since 1800 according to Berkeley Earth.

The temperature anomalies used to calculate the trend in Fig. 72.2 were determined using the raw data from each station. However, if we average the anomaly data for the 34 long and medium stations using not the original raw data, but the adjusted data that Berkeley Earth create from the raw data (both adjusted and unadjusted data sets are listed in the data files on their website), the result is the temperature time series shown below in Fig. 72.5. These trends are very similar to the official Berkeley Earth trends shown in Fig. 72.4 above.

Fig. 72.5: Temperature trends for Pakistan based on the average of anomalies for all long and medium stations using Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1891-2010 and has a gradient of +0.91 ± 0.03°C/century.

The difference between the Berkeley Earth temperature trend in Fig. 72.5 that is based on adjusted data, and the trend derived solely from raw data shown in Fig. 72.2, is shown in Fig. 72.6 below. As Fig. 72.6 shows, the breakpoint adjustments added to the data by Berkeley Earth add over 0.5°C of warming between 1975 and 2005. This explains why the official Berkeley Earth trends in Fig. 72.4 are so different from the trends that result from the actual raw data in Fig. 72.2.

Fig. 72.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 72.5 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 1881-2010 has a positive gradient of +0.304 ± 0.009 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

Finally, if we compare the data for Pakistan in Fig. 72.2 with the equivalent data for India (see Fig. 71.6 in Post 71) we see that there are both significant differences and similarities between the two temperature trends. The overall temperature changes from 1930 onwards are broadly the same (an increase of about 0.5°C), and many of the peaks in the two different 5-year moving averages coincide (see Fig. 72.7 below). But the overall level of agreement is much less than we have seen for trends for different countries in central Europe (see Post 57) and for different subsets of data for the USA (see Post 67). 

The reason for this is that the stations for India and Pakistan are over 1000 km apart on average. This means that India and Pakistan are much less likely to share a common climate than Austria and Germany are (where the stations are less than about 200 km apart on average). As I showed in Post 11, the spatial separation of weather stations is an important factor in determining the degree of correlation between them in their temperature signals.

Fig. 72.7: A comparison of the 5-year moving average temperature trends for India (blue) and Pakistan (red).

Summary

The mean temperature time series for Pakistan has three distinct epochs, each with a different trend (see Fig. 72.2).

Before 1938 there is some moderate warming of about 0.5°C, but this part of the mean temperature time series is based on only seven temperature records (see Fig. 72.3), most of which are located near major cities.

Between 1938 and 1997 the climate is fairly stable with a slight cooling trend. The data for this epoch is likely to be the most reliable as it is derived using data from between 19 and 34 different station records. This epoch also corresponds to a period when carbon dioxide levels in the atmosphere increased by 18% from 310 ppm to 365 ppm, yet apparently this had no impact on the local climate.

Finally, just after 1997 there appears to be an abrupt increase in temperature of about 0.65°C, which appears inexplicable. This period also coincides with a rapid increase in the number of active stations in the region (see Fig. 72.3), many of which have large gaps in their records in the 1980s and 1990s. So, the reliability of data for this epoch is questionable as well.

The adjusted data created by Berkeley Earth claims the temperature rise since 1900 to be over 1.5°C (see Fig. 72.5), of which over 0.5°C is the result of breakpoint adjustments added after 1995 (see Fig. 72.6).

Conclusions

There was no climate change due to carbon dioxide emissions in Pakistan before 1997.

The sudden temperature rise after 1997 could be the result of global warming, local climate instability, or it could be the result of other factors such as increased energy usage, or maybe even systemic changes to the data collection process. Whatever the cause, what is clear is that the temperature rise is much more modest than climate science would like us to believe.