Roy Spencer claims, without proof, that they do. Berkeley Earth (BEST) found they do not, after having actually examined the global thermometer set six ways from Sunday with a skeptical eye:
"The Urban Heat Island effect is real. Berkeley’s analysis focused on the question of whether this effect biases the global land average. Our UHI paper analyzing this indicates that the urban heat island effect on our global estimate of land temperatures is indistinguishable from zero."
http://berkeleyearth.org/faq/#question-15
paper:
"Influence of Urban Heating on the Global Temperature Land Average using Rural Sites Identified from MODIS Classifications," Wickham et al., Geoinfor Geostat: An Overview 2013, 1:2
http://dx.doi.org/10.4172/2327-4581.1000104
https://www.scitechnol.com/2327-4581/2327-4581-1-104.pdf
And indeed, that's been the determination for some decades; here's a 1990 paper from Nature:
At the Astrobiology conference I was at a couple of weeks ago, a speaker said that on Earth cities occupy 0.2% of the globe's surface area. (It was in the context of the possibility we might see lights on an exoplanet's surface.) I also learned a new word then: "ecumenopolis" -- a planet whose entire surface is covered by one gigantic city.
If there are no UHIs, i.e. no net UHI, then the global mean average temperature (GMAT) is
Now let's say there is a UHI, the same in all cities, and those cities occupy a certain area. Then the GMAT would be something like this weighted average:
(Apologies for the different font sizes.) So the difference in GMAT between a world with a UHI and one with no UHI is
The ratio on the right-hand side is 0.002, and the urban heat island effect is, what, about 5 K (=9°F)? Then
That's your UHI. The trend will change even slower than this, per decade.
Even if the area of all the cities doubles, it will still be only about 0.02 K << global warming of 1 K.
Just a back of the envelope calculation, but it suggests the UHI is indeed small-to-negligible. Because the Earth is vaaaaaaaaaaaaaast.
"The results show that the urbanization influence in two of the most widely used hemispheric data sets is, at most, an order of magnitude less than the warming seen on a century timescale."Is there a way to estimate the influence of the UHI? Here's my attempt.
"Assessment of urbanization effects in time series of surface air temperature over land," P. D. Jones et al, Nature, volume 347, pages 169–172 (1990).
https://www.nature.com/articles/347169a0
At the Astrobiology conference I was at a couple of weeks ago, a speaker said that on Earth cities occupy 0.2% of the globe's surface area. (It was in the context of the possibility we might see lights on an exoplanet's surface.) I also learned a new word then: "ecumenopolis" -- a planet whose entire surface is covered by one gigantic city.
If there are no UHIs, i.e. no net UHI, then the global mean average temperature (GMAT) is
Now let's say there is a UHI, the same in all cities, and those cities occupy a certain area. Then the GMAT would be something like this weighted average:
(Apologies for the different font sizes.) So the difference in GMAT between a world with a UHI and one with no UHI is
The ratio on the right-hand side is 0.002, and the urban heat island effect is, what, about 5 K (=9°F)? Then
That's your UHI. The trend will change even slower than this, per decade.
Even if the area of all the cities doubles, it will still be only about 0.02 K << global warming of 1 K.
Just a back of the envelope calculation, but it suggests the UHI is indeed small-to-negligible. Because the Earth is vaaaaaaaaaaaaaast.










