How can you blame the advertisers?
It's the same X,XXX watts to transmit the signal regardless of TV programming or commercial time, and doesn't change unless more or less people are watching. And it then becomes a function of personal electricity consumption. Want to generate less carbon? Turn off the damned TV and do something.
It has nothing to do with the advertisers though. If no-one watched TV (the biggest component of the carbon cycle that worries them so much), they wouldn't advertise.
So, greenies: stop watching TV. If American Idol got 500K less viewers, that would be about 100 megawatt-hours saved on the power grid (at 200watts per TV, a low number).