Classifying land-based temperature stations as “Urban” or “Rural” in UHI studies does not demonstrate anything about false temperature trends.

From Dr. Roy Spencer’s Global Warming Blog

by Roy W. Spencer, Ph. D.

The more time I spend on a research project, the more time I have to reflect on what others simply consider true. And in the process, I sometimes have an epiphany rather than a clarification of my thoughts on a subject.

As I continue to investigate how to quantify urban heat island (UHI) effects with the aim of determining the extent to which land surface temperature trends have been artificially inflated by urbanization effects , there is a recurring theme that I found was not handled well in previous installments. published articles on this topic. I’ve mentioned it before, but it’s so important it deserves to be posted on its own (brief) blog.

It concerns the popular assumption that “urban” thermometer locations experience spurious warming over time, while “rural” locations do not.

Obviously, at any given time, urban environments are warmer than rural environments, especially at night. And urbanization has increased around temperature monitoring sites over the past 50 to 100 years (and beyond). However, several studies over the years have found that urban and rural areas tend to have very similar temperatures. This has led investigators to conclude that temperature data sets such as the Global Historical Climate Network (GHCN), especially after “homogenization”, are largely free of warming effects. created by the process of urbanization.

But the conclusion is wrong… all it shows is that the temperature trends between rural and urban areas are similar… not that those trends are unaffected by urbanization effects.

Instead of, Studies have demonstrated that the greatest rates of warming as populations increase are in areas near rural, not urban. The one-quarter power relationship is found by Okay (1973) and other things (and what I’m also finding in the summer GHCN data) means that population density increases from 1 to 10 people per square kilometer (both “rural”) creating warming more than an urban area growing from 1,000 to 1,700 people per square kilometer.

Therefore, “rural” locations cannot be considered immune to artificial warming from urbanization. This means that studies comparing “rural” to “urban” temperature trends haven’t really proven anything.

The mistake people have made is assuming that it’s just because urban locations are warmer than rural locations at any point in time that they then have a much larger false warming effect on trend over time. That is simply not true.