This should be negligible. It isn't significantly different from burning fossil fuels at a rate far higher than they are being created. However, it's *just* waste heat, and not adding an insulation effect the way greenhouse gasses do. So, it should represent a net improvement over the current status quo.
Yeah, it might be marginally higher than no energy use, but it's certainly less warming than most commonly employed methods by a ludicrous factor.
Furthermore, the earth isn't a closed energy system. Waste heat can and does escape. It's like having a hotter fire instead of building a house with insulation. There'll be some additional warmth, but it isn't going to stick around.
So, at least at anything vaguely close to current population levels, it's not a problem at all.
Now, what happens as a result of problem being sucked out of the big bang way back in time...no idea. Sky's the limit there.