Urban areas can be warmer than surrounding non-urban areas because there is a lot of combustion, pavement and other structure can collect solar heat and retain it for a while, and other factors. It is not uncommon to look at a weather map where conditions for precipitation are marginal, and everywhere but the urban zone, or only the urban zone and nothing else, is showing a weather phenomenon. Because people and airports (where weather is very important) are located in or very near urban areas, it stands to reason that a lot of the data used to estimate global temperatures would be affected by any urban effects, and if urban areas are a) warmer than surrounding areas and b) increasingly warm over time then “global warming” may well be an artifact of the urban heat island effect. That wouldn’t necessarily make it a hoax, but it would make it wrong. We would then have to revise our understanding of certain aspects of physics because we expect global warming to occur in CO2 levels go up, but physics has been revised before. Kepler was wrong, Newton was wrong, maybe the climate change scientists are wrong too….