If there is one country in the world where you expect dramatic climate change on account of its own greenhouse gas emissions, then that country would probably be the USA. And if there is one state in the USA that embodies the American passion for fossil fuels, that state would be Texas. So when Texas was hit by extreme weather earlier this month in the shape of winter storms Uri and Viola, which resulted in millions Texans losing their electricity supply, then it was only a matter of time before people started screaming "climate change". Because even extreme cold weather is a symptom of anthropogenic global warming (AGW) and climate change (apparently). Unfortunately there is just one problem: there has been no global warming in Texas. So, given the topical nature of the Texas climate at the moment, I thought I would take a temporary break from Europe and take a closer look at climate change in Texas.
The mean temperature trend for the region is shown in Fig. 52.1 below. This was achieved by averaging the temperature anomalies from the 220 longest weather station temperature records in the region, where the temperature anomalies were measured relative to the monthly reference temperature (MRT) in each case. The MRTs were calculated for the interval 1961-1990. For a more detailed explanation of the MRT calculation process, see Post 47.
For 160 years up to 2013 there was no anthropogenic global warming (AGW) occurring in Texas. In fact the mean temperature for the region rose by less than 0.08 °C. And while there is some evidence of a rise in temperature since the 1960s, this still leaves temperatures lower than in the first half of the 20th century.
Fig. 52.2: The number of station records included each month in the mean temperature trend for Texas.
The temperature trend shown in Fig. 52.1 is the average of up to 220 of the longest temperature records for the state as illustrated in Fig. 52.2 above. All the temperature records have over 720 months (or 60 years) of data, of which 64 are long stations with more than 1200 months of data. These 220 stations are also distributed fairly evenly over the region as shown in Fig. 52.3 below. This means that a simple average of all the temperature anomalies without additional weighting coefficients should yield a mean temperature trend that is reasonably accurate, even though there does appear to be a slightly higher density of stations in the east of the state than in the west. This conjecture will be tested by comparing results later.
Fig. 52.3: The locations of long stations (large squares) and medium stations (small diamonds) in Texas. Those stations with a high warming trend are marked in red.
The other point of note about the stations in Fig. 52.3 is the high proportion of stations that appear to exhibit no warming; over 70% of them. Here, a warming station is defined as being one where the temperature gradient is more than twice the uncertainty in the trend and the total temperature rise also exceeds 0.25 °C.
This high proportion of cool stations is unusual but not unique. It has seen in many other places including New South Wales and Victoria. What it appears to highlight is the strong correlation that exists between the degree of warming seen at a particular location and the size of the local population, degree of economic development and the length of the temperature record itself.
Short, younger temperature records tend to exhibit greater warming because they only have data from the latter part of the 20th century and post 2000, and increased urbanization in the latter part of the 20th century is clearly warming the local environment. In fact, direct anthropogenic surface heating (DASH) or waste heat equating to about 0.7 W/m2 has probably warmed Texas by up to 0.3 °C since 1850. In addition, the short length of modern station records means that they do not include any of the natural variation seen in earlier times such as naturally high temperatures seen in the 19th century. In addition, many rural stations appear to exhibit very little warming, while major cities like Jakarta, Sydney and Melbourne can display very large degrees of warming that do not correspond to the climate of the rest of their regions.
What is interesting is comparing the trend based on the original true temperature data in Fig. 52.1 with the equivalent trend based on an average of the adjusted data used by Berkeley Earth. This adjusted data includes the effects of homogenization and breakpoint adjustments that are supposed to improve the quality and accuracy of the data. The mean of the adjusted Berkeley Earth data for the 220 longest station records in Texas is shown in Fig. 52.4 below.
Fig. 52.4: Temperature trend in Texas since 1840 derived by aggregating and averaging the Berkeley Earth adjusted data for the 220 longest data records for Texas. The best fit linear trend line (in red) is for the period 1881-2010 and has a gradient of +0.58 ± 0.04 °C/century.
Unlike the original data in Fig. 52.1 which exhibits virtually no warming, the Berkeley Earth adjusted data has a strong positive trend of 0.58 °C per century. In total this equates to a warming of over 0.8 °C from 1880 to 2010, while the 10-year moving average suggests an even greater warming of over 1.2 °C. Again, this may be consistent with IPCC reports, but it is not consistent with the actual real data in Fig. 52.1. It is, however, virtually identical to the published Berkeley Earth version shown in Fig. 52.5 below.
Fig. 52.5: The temperature trend for Texas since 1820 according to Berkeley Earth.
The similarity of the data in Fig. 52.4 with the Berkeley Earth published version shown in Fig. 52.5 above in effect validates the simple averaging process I have employed, not only for the data in Fig. 52.4, but also for that in Fig. 52.1 as well. It demonstrates that weighted averages are not needed.
Fig. 52.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 52.4 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 1911-2010 has a gradient of +0.568 ± 0.003 °C per century. The orange curve shows the contribution from breakpoint adjustments only.
Overall, the Berkeley Earth adjustments appear to add between 0.6 °C and 1.2 °C to the warming of Texas, depending on how you view it. If we consider the net adjustments made to the data (the blue curve in Fig. 52.6 above) which are the difference between the mean anomalies in Fig. 52.1 and Fig. 52.4, these appear to add about 0.6 °C of warming. On the other hand, the difference in the gradients of the best fit lines in Fig. 52.1 and Fig. 52.4 results in over 0.7 °C of warming being added. Either way, these are significant modifications to the original real data that completely change its properties.
Summary
1) The mean temperature of Texas has been stable since 1840 (see Fig. 52.1).
2) In contrast, the Texas temperature trend based on Berkeley Earth adjusted data exhibits a warming of over 0.8 °C before 2010 (see Fig. 52.4).
3) Virtually all the warming seen in the Berkeley Earth adjusted data (as denoted by the trend of 0.58 °C per century in Fig. 52.4) can be accounted for by the adjustments made to the data (as seen in the trend of 0.57 °C per century in Fig. 52.6).
4) Adjustments made to the temperature data by Berkeley Earth via breakpoint adjustments and homogenization (see Fig. 52.6) have profoundly changed the magnitude of the warming of the Texas temperature trend since 1840 (see Fig. 52.4) compared with that observed in the raw original data (see Fig. 52.1).
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