I though the attached might be interesting. It shows little more urban related trend in NY over the 20th century. Also on warmest days it is warmer outside the city. This is probably unique to NY. The reason LWC [London Weather Centre?] isn't as warm as LHR [London Heathrow Airport] on the very warmest days is because the measurements are 50m up on a building! Cheers Phil
For example, the Urban Heat Island effect causes New York City to be about 5 degrees warmer than surrounding suburbs and accounts for 5 to 10 percent of summer electricity use.