This section of the DOE report starts with one of those points that should be obvious but is too-often swept under the rug by alarmists: our record of temperatures over land was collected where people live. And people have been changing their surroundings over time, especially by building large cities whose man-made structures and materials, such as asphalt trap heat, driving up thermometer readings for reasons unrelated to climate change. So the fact that such records in some places go back to the 1800s doesn’t mean we have good data for measuring climate change. What we need is a record of what the air temperature would have been if the land surface had never changed. But pristine locations, by definition, are where no one has lived, so with rare scientifically-dedicated exceptions no one was writing down the daily temperatures there. As the DOE team states, in a tone more diplomatic than we would use, “The IPCC acknowledges that raw temperature data are contaminated with UHI effects but claims to have data cleaning procedures that remove them. It is an open question whether those procedures are sufficient.” They then proceed to unravel the IPCC claim and close the question.
The section begins by reporting that the most recent IPCC report (the “AR6”) insisted that urbanization bias added no more than 10 percent to the measured warming trend. But they didn’t have any evidence to offer, they were just repeating what they had said in their previous report (“AR5”). But that report also made the claim without citing a source. The one before that (“AR4”) had cited a source, but the paper they cited didn’t have any data to support the claim, it just offered it as a conjecture. Guesses all the way down.
Meanwhile in the years leading up to the AR4 papers had appeared in the climatology literature arguing that urbanization and related influences added something more like 30 to 50 percent to the measured warming trend. The AR4 dismissed those findings by claiming they were artifacts of natural variability and lacked statistical significance, but (drum roll please) offered no supporting evidence. Subsequent studies showed that the IPCC’s claims were untrue and deep in the back pages of the AR5 the IPCC admitted that, uh, heh heh, we made it up. But they stuck to the 10 percent claim anyway.
The DOE report section goes on to argue that the problem with the way IPCC authors have tried to measure the urbanization contamination problem is not merely that it has not been shown to work. It’s far worse. It has been shown not to work. It demonstrably doesn’t find this effect even in data independently known to be contaminated.
Our suspicions about the biases of the land-based warming record persist because the people whose job it is to investigate the topic keep sweeping the evidence under the rug. Then they say there’s no evidence. Sure, nothing to see here folks, other than thousands of acres of roads and high-rises where there used to be trees and fields.
Absence of evidence is not evidence of absence, especially when the evidence keeps getting paved over.
