I have written many times challenging claims of Sierra Global warming on my blogs. There is one weather station at Lake Tahoe, which over history has been affected by urbanization, that is often cited in studies and papers as proof of Sierra warming. Details HERE.
A family of 3 papers have been published to examine urbanization bias. These papers validates my claims that Sierra Warming is the result of weather station urbanization.
Summary: “Urbanization bias” – Papers 1-3
Many areas around the world have become highly urbanized over the last century or so. Records of weather stations which are located in urbanized areas may show artifical warming trends due to urbanization bias.
In this essay, we summarise the main points of our three “Urbanization bias” papers, which we have submitted for peer review at the Open Peer Review Journal.
It has been known since at least the 19th century that urban areas are warmer than rural areas. This is known as the “urban heat island” effect.
This is a serious problem for estimating global temperature trends because many weather stations are now showing warming from an urban heat island, which wouldn’t have been there 100 years ago. That is, gradual urbanization has introduced an artificial warming bias into their weather records. This bias is called “urbanization bias”.
Since the 19th century, and particularly in the last few decades, the world has become increasingly urbanized. Urban areas still only comprise about 1%. So, this doesn’t really have much impact on actual global temperature trends. But, about half of the weather stations used for analysing global temperatures are in urban areas. As a result, the estimated global temperature trends are seriously affected by this bias.
These estimated global temperature trends are the main basis for the claims that there has been “unusual global warming” since the Industrial Revolution. This means that much of the “global warming” that people are worried about is probably just urbanization bias!
Despite that, several studies have claimed that urbanization bias isn’t a problem. So, in Paper 1, we carefully analysed these studies to see if their claims were justified. In all cases, we found that they weren’t! It turns out that the authors of those studies had each made basic errors and/or hadn’t looked at their data carefully enough.
One of the groups using weather records to calculate global temperature trends has developed a computer program which they believe has removed the urbanization biases from their data. However, in Paper 2, we analysed this program in detail and found that it didn’t work. It actually introduced as many biases as it removed!
In Paper 3, we studied the main weather station archives used for calculating global temperature trends, i.e., the Historical Climatology Network datasets.
The U.S. component of the datasets was the most reliable component and most of the U.S. stations were fairly rural. However, we found that urbanization bias had introduced an artificial warming trend of about 0.7°C/century into the urban stations. To put this in context, the “unusual global warming” that has allegedly occurred since the Industrial Revolution is supposedly about 0.8°C/century.
For the rest of the world, the Historical Climatology Network datasets didn’t actually have enough rural stations with sufficiently long records to estimate global temperature trends. Only EIGHT of the rural stations had data for at least 95 of the last 100 years!
This means that the claims that there has been “unusual global warming since the Industrial Revolution” are mostly based on data from urban stations, and much of it is probably an artefact of urbanization bias.
The paper are long and complex. The full details are HERE.