Anthony Watts has a post up purporting to show a very large UHI effect in Reno, Nevada.
I will just take his numbers and methods at face value, even though many questions come to mind. After all, 10oF is a big jump from outskirts to downtown, but maybe that is correct and not contaminated from engine heat. Also note this, which is specifically about Reno and shows how the UHI effect is removed from the data.
(pretty convincing, no?)
The problem is the conclusion that is at the very least strongly implied: if Urban Heat Islands are that pronounced, maybe global warming is just an artifact of that.
As this is a very common contrarian talking point, I do have a guide article about it: “Global warming is due to the Urban Heat Island effect“, and the points are all covered there.
I only want to reemphasize that UHI is real, no one disputes that! So it is accounted for in the reconstructions. I also want to present again something that strikes me as rather irrefutable evidence that a global warming signal is not the result of primarily urban readings. The evidence is in the images below and the plain-as-night-and-day fact that there is no correlation between warming regions of the globe and urbanization. If the “it’s just UHI” folks were correct, then the global hotspots would by and large be over areas with lots of development.
Here is a global anomaly map for 2000-2006 with 1951-1980 baseline:
and here is a satellite image of global urbanization:
Note the complete lack of correlation for Canada, China, USA, India, Asia, Eastern Europe, Africa and the poles. Also note that the one place with strong correlation between urban centers and warming, western Europe, is also the place where urbanization has changed the least, the cities are hundreds of years old and have developed much less over the last 50 than North and South America.
So. Where’s the beef?