[justa-hairyape]

Kinda hard to state something that has not been quantified is insignificant, when it has not even been quantified. Apparently the only reason CO2 is theoretically a problem is due to the increased water evaporation that occurs (feedback) due to the trapped heat from the CO2. So any generated heat effects get amplified by the resulting increased water evaporation. And urban areas are definitely sources of water vapor.

[marktwain]

The total energy consumed by people from constructed sources, oil, coal, hydroelectric, nuclear, etc. is about the equivalent of 1.05 billion tons of oil per year. That includes far more than all the oil burned by all the motors in a year. It includes coal fired plant, nuclear plants, everything that uses energy in any kind of technology.

The total energy received by the Earth from the Sun is equivalent to 131,400 billion tons of oil per year.

The total heat output of all of man's works is less than .00008 of the solar input. There is no way that we can measure the temperature that closely. The variability of the clouds on a single day may be more than that. It is less than 1/10,000 of the heat input to the planet.

I believe that to be insignificant in the overall heat budget. Here is where I found the numbers.

http://www.mpoweruk.com/solar_power.htm

This is not to indicate that there is no “heat island” effect in urban centers. That effect is real, but is different from the heat input into the total Earth heat budget, and includes a lot of energy streams going in and out of urban heat islands due to the large presence of so much asphalt and concrete, and so few trees, more than anything else.