In the past month I have shown some detailed response of the Earth’s temperature to global events. Examples of this are the ENSO and volcanic eruptions. By comparing the temperature anomaly between the satellite and the station methods for these events, it has become clear that the station method is becoming less sensitive to these events over time.
The main problem with the station behavior is that over the past 20 years the measured global temperature has started to diverge more from the satellite method. This leaves everyone with different choices as to what data they use to look for global warming and the results are substantially different. It is clear why the satellite method is more responsive at detecting global temperature change, but that doesn’t explain why the station method is becoming less effective over time.
Long time followers of the global warming debate will know that the Urban Heat Island (UHI) effect is commonly used to explain the problem, but it isn’t enough by itself. The UHI certainly has an influence on some stations, but the urban effects are not enough to explain the entire problem of why the station method has shown twice as much warming as it should have.
A private group named the Science and Public Policy Institute recently released a very detailed study of the station method of measuring temperature over a large area. The results are very interesting and point out some of the reasons why the station method of measurement has shown more warming than it should. Including some reasons that are not commonly being discussed.
The study focuses only on the stations in the state of Utah. The study takes 36 stations and breaks them down into three different categories.
Urban Stations: 11 in total
Agricultural Stations: 12 in total
Low Impact Stations: 13 in total
By performing an in depth study of each station from 1948 to 2009 they determined the rate of warming for each type of station. The paper provides more detail, but the end result is the following seasonal temperature response.
The chart in its original form was in °F/year and I have converted it to °C/decade which is more conventional. Surprisingly, the agricultural stations show more warming than the low impact stations. I would have expected a greater similarity between them, but the results are different.
The theory proposed in the study is that agricultural regions perform irrigation which has the result of increasing the local dewpoint. Increasing the water vapor content in the air around a station has the effect of insulating the atmosphere from losing temperature as much during the night. This is also something that would contribute to the overall UHI as well.
The warming trend for the low impact is also the most consistent between the max and minimum temperatures in both the summer and the winter. The Urban and Agricultural stations have enormous differences in when the warming is taking place. That is the the signature of the change in land use. Because the minimum temperatures are being artificially elevated, it is making the stations less sensitive to natural cooling effects like volcanoes and La Nina’s.
The overall decadal warming for each station type is here:
Now compare this to the warming trends that are shown from 1979-2010 for the station and the satellite methods.
The warming rate for the global station method in the past 30 years is right between the Urban and Agricultural station results.
This study provides a solid and credible reason for why the stations are showing a decreased sensitivity to global events. The insignificant response to the recent two ENSO events is very curious. This study provides evidence that shows why the station methods are showing more warming while at the same time also being less responsive to cooling events that happen.