Davin News Server

Urban Heat Island Paper Has Been Published - May 15th, 2025 by Roy W. Spencer, Ph. D.

It took the better part of two years to satisfy the reviewers, but finally our paper Urban Heat Island Effects in U.S. Summer 
Surface Temperature Data, 1895-2023 has been published in the AMS Journal of Applied Meteorology and Climatology.

To quickly summarize, we used the average temperature differences between nearby GHCN stations and related those to population 
density (PD) differences between stations. Why population density? Well, PD datasets are global, and one of the PD datasets goes 
back to the early 1800s, so we can compute how the UHI effect has changed over time. The effect of PD on UHI temperature is 
strongly nonlinear, so we had to account for that, too. (The strongest rate of warming occurs when population just starts to 
increase beyond wilderness conditions, and it mostly stabilizes at very high population densities; This has been known since 
Oke's original 1973 study).

We then created a dataset of UHI warming versus time at the gridpoint level by calibrating population density increases in terms 
of temperature increase.

The bottom line was that 65% of the U.S. linear warming trend between 1895 and 2023 was due to increasing population density at 
the suburban and urban stations; 8% of the warming was due to urbanization at rural stations. Most of that UHI effect warming 
occurred before 1970.

But this does not necessarily translate into NOAA's official temperature record being corrupted at these levels. Read on... 

What Does This Mean for Urbanization Effects in the Official U.S. Temperature Record?

That's a good question, and I don't have a good answer.

One of the reviewers, who seemed to know a lot about the homogenization technique used by NOAA, said the homogenized data could 
not be used for our study because the UHI-trends are mostly removed from those data. (Homogenization looks at year-to-year [time 
domain] temperature changes at neighboring stations, not the spatial temperature differences [space domain] like we do). So, we 
were forced to use the raw (not homogenized) U.S. summertime GHCN daily average ([Tmax+Tmin]/2) data for the study. One of the 
surprising things that reviewer claimed was that homogenization warms the past at currently urbanized stations to make their 
less-urbanized early history just as warm as today.

So, I emphasize: In our study, it was the raw (unadjusted) data which had a substantial UHI warming influence. This isn't 
surprising.

But that reviewer of the paper said most of the spurious UHI warming effect has been removed by the homogenization process, which 
constitutes the official temperature record as reported by NOAA. I am not convinced of this, and at least one recent paper claims 
that homogenization does not actually correct the urban trends to look like rural trends, but instead it does "urban blending" of 
the data. As a result, which trends are "preferred" by that statistical procedure are based upon a sort of "statistical voting" 
process (my terminology here, which might not be accurate).

So, it remains to be seen just how much spurious UHI effect there is in the official, homogenized land-based temperature trends. 
The jury is still out on that.

Of course, if sufficient rural stations can be found to do land-based temperature monitoring, I still like Anthony Watts' 
approach of simply not using suburban and urban sites for long-term trends. Nevertheless, most people live in urbanized areas, so 
it's still important to quantify just how much of those "record hot" temperatures we hear about in cities are simply due to 
urbanization effects. I think our approach gets us a step closer to answering that question.

Is Population Density the Best Way to Do This?

We used PD data because there are now global datasets, and at least one of them extends centuries into the past. But, since we 
use population density in our study, we cannot account for additional UHI effects due to increased prosperity even when 
population has stabilized.

For example, even if population density no longer increases over time in some urban areas, there have likely been increases in 
air conditioning use, with more stores and more parking lots, as wealth has increased since, say, the 1970s. We have started 
using a Landsat-based dataset of "impervious surfaces" to try to get at part of this issue, but those data only go back to the 
mid-1970s. But it will be a start.

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May:

Urban Heat, Not Climate Change - A New Study By Dr. Roy Spencer

James Hansen Canceled By His Own Climate Cult

Heavy Mid-May Snow Hits Poland

Europe And East Asia Buck Heatwave Narrative

Concordia Continues To Cool

Record US Ski Season Defies Alarmist Predictions

Record May Cold In Bâlea Lac

Concordia At -107.1F

Mainstream Damage Limitation After Antarctic Ice Growth

Cold Sweeps Japan After Historic Winter Snow

Record May Snow Slams Goose Bay
Concordia At -106.1F
Antarctica Had Far Less Sea Ice Just 1,000 Years Ago
Snow And Record May Lows Hit Europe
No May Trend
-100F Returns To Antarctica
May Frosts Persist In Europe
Mumbai Logs Coldest May Temp Since Records Began (In 1881)
Volcanoes That Changed The Modern World
NOAA Pulls Plug On "Billion Dollar Disasters" Database
Mumbai Coldest May Temp Since 1985
Tasmania Sees Snow As Cold Front Grips SE Australia
Atlantic Cools Sharply As Global Temperatures Dip
Another New Study Blows Hole In Antarctic Warming Claims
Snows and Sub-Zero Lows Sweep Europe
Ice Recovery At Both Poles
UK Carbon Prices Soar
A Scholarly Takedown Of The Net-Zero Agenda
Mt. Hutt Sees Record Early May Snowfall
Cherry Blossoms In The Snow
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Another New Study Finds Antarctica Is Gaining Ice
Japan's Summer-Only Ski Resort Opens With Record Snowpack
Historic May Snowfall Hits Moscow Region
Snow Returns To UK
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No Warming Across The High Southern Latitudes
Heat Hysteria: A Manufactured Crisis Built On Asphalt
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Taiwan Shivers Through Cold Spring
Russia Slammed By Record Late-Season Snowstorm
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