Once again it is time for the 2011 regional temperature update. This is the series where I show how the temperature and the temperature anomaly for the year in the region I live in. I also use this to show the Urban Heat Island (UHI) effect for the city of Boise. I do that by comparing to the daily temperatures of McCall which is a more rural town located ~100 miles away from Boise.
In one more example of the every shifting quicksand of monitoring the climate, the baseline averages for the daily temperatures have been changed in the past two months. I noticed this when I was trying to get the update done in early September. That is the main reason why the update is a little late. I did a comparison between the two sets of data and the change was interesting, but not very substantial. Since it made little difference to the final numbers this is more of an informational statement.
Part of the purpose of this series of articles is to demonstrate the limitations of temperature anomaly. It is for this reason that instead of just showing the temperature anomaly for the year, I show the high and low temperature and the average temperature for the entire year. For the locations of Boise and McCall the year is more than 75% complete so it is possible to see the seasonal changes in the temperature and the average temperature.
These two charts show that the actual temperature is always varying up and down for both the high and low temperatures. That means that the temperature anomaly is also in constant flux. If I used the temperature anomaly to define the temperature for the two locations for the entire year, the above charts would be boiled down to:
Boise: -0.17 °C
McCall: -0.81 °C
If I further merged these numbers I would get -0.49 °C. I argue that this is a fairly useless number in describing what the climate has been for the year. I say that even though the anomaly for the year is significantly below average (based on typical definitions). Such a amalgamation of data also hides the fact that Boise experiences a measurable UHI of ~1 °C for the average temperature anomaly.
So while I do deal with temperature anomaly on a regular basis because it is the standard measure of the Earth’s temperature, it is not a very useful standard, or at least it is not useful by itself. For instance, here are the daily high temperature anomaly’s for the year so far.
The anomaly is heavily impacted by weather patterns that take place during each season. There is no predictive value in the anomaly for what will happen next. The warm September that did happen in both places has no predictive value for October. October will be cooler than September and the October anomaly is not influenced by the positive anomaly that took place in September. The very end of all charts show how quickly fall arrived in both locations.
The rural location of McCall has consistently had a lower temperature anomaly for the year than the urban Boise location. What is most interesting is how the differences in locations have played out over the year.
High Temperature UHI: -2.3 °C
Low Temperature UHI: 0.3 °C
Mean Temperature UHI: -1.0 °C
A UHI between a rural and urban location of -1.0 °C is pretty typical. What is most interesting is how much cooler the daily high temperatures have been in the rural area. Each season had some difference in behavior in the anomaly for the high/low/mean temperature.
It is the high temperatures that have been the most abnormal for the year. They have been well below average for most of the year, but especially in the Spring. Boiling down the entire year into a single number takes away all understanding of what the weather was like for the entire year. That Boise almost has a “zero” anomaly for the year provides no useful information for describing the year, especially considering that most of the year has had high-temperature that are well below normal.
Using only the temperature anomaly is perhaps the worst possible way to study the Earth’s climate. Perhaps that is why it is the preferred method by those that wish to say that the Earth is behaving in an abnormal fashion.