[wizofaus]

Globally that's true, but perhaps more relevant when considering the part of the biosphere that humans primarily inhabit? To what degree is the urban heat island effect caused by artificially heated air (including waste heat from A/Cs), for instance?

[supertrope]

Urban heat island effect is cause by cutting down too many trees (which reflect infrared) and paving over the majority of the surface. Here too mechanical heat is dwarfed by sunlight.

[wizofaus]

I'm not so sure, I can't find numbers but it is commonly listed as a secondary factor (including by wikipedia).

I did find this: "Results show that the urban heat island causes an average increase of 2.2 °C in the external air temperature mainly caused by the waste heat rejected from cooling system" (https://www.mdpi.com/2225-1154/9/3/48/htm)

And while it's true UHIs don't significantly contribute towards climate change, they can cause increased rainfall, and presumably have some effect on agricultural production that's done near larger cities.

[Schroedingersat]

You underestimate how wasteful suburban life is. If you have 2,000 people in a square kilometer all burning tens of kW of petrol in their cars and running multi kW AC systems in their homes and their office as well as pools, giant LED billboards and whatever else it starts to give sunlight a run for its money.

[yobbo]

How much oil is required to heat the air over Los Angeles by 2C?

(Facts quickly googled)

Area of Los Angeles: 1.29 * 10⁹ m²

Height of air column over city: say 1000m

Volume of air = 1.29 * 10¹² m³

Mass of air (density 1.29 g/l) = 1.66 * 10¹² kg

Energy of air (700 J/kg for each C) = 2.32 * 10¹⁵ J

Equivalent number of barrels of oil (6.1 * 10⁹ J) = 380327 ~= 0.4 * 10⁶

Daily consumption in all of california: 1.8*10⁶ barrels

If the calculations are right, you would have to burn around 20% of California's daily consumption inside the city to raise the air temperature by 2C.