"Yes, the cause is the question. I agree that the quick answer is “humans” and their use of “energy” nuclear or otherwise. ( energy is defined as “Amount of work done [or technically, do-able - but now we're into thermodynamics which gets messy... By Nick at Space Sciences: http://www.habitablezone.com/nexus/index.asp?svcpt=space

(By quoting Nick, I hope that the meaning of the word will become clear. :-) "

Not really. I can assume that "“humans” " is some kind of technical glitch which probably is humans in quotes. And I can assume you intended to refer to a specific post by Nick instead of giving a link to the entire Space board.
Btw copy link location gives: http://www.habitablezone.com/currentevents/messages/463463.html
A link to my post above.

Moving on:
"I also agree that

““there are probably things that could be done which would have significant affect on local temperature.”

“

One method would be to improve the efficiency of all devices that will use energy to do work."

I think there has been a fair amount effort already in this area- though no doubt more could be done, but I don't see this as a fruitful approach. First, one needs to identify the problem [you know, like, is there any problem and where are there any problems]. Or I guess even more basic, one needs to understand that Urban areas are a small proportion of total global area. So what I'm saying is that Urban Heat islands are more significant in terms of regional affects than any affect upon global climate or temperature. The idea that because they have little affect upon the globe, should not be *translated* into meaning it is insignificant. AND all idiocy about "Global Warming" in general is masking potential solutions because the general focus is misdirected.