re: True enough, but...
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. :-)
I also agree that
““there are probably things that could be done which would have significant affect on local temperature.â€â€œ
One method would be to improve the efficiency of all devices that will use energy to do work.