The deniers don't have to be proven correct to prevent action on climate change, they just have to put out enough FUD to create doubt.
Cigarettes, seat belts, lead paint, asbestos, Linux, climate change. They've all been fought using the same tactics.
Going back, worldwide, to a pre-industrial civilisation would be a possibility. However, We're looking at 90% fatality rates to get to that point due to lack of food production. Probably would be even less than that. No chance in happening, unless forced by catastrophic event.
Another possibility is tremendous rationing. We see what having even simple healthcare is in this country. Instead, we would look at rationing everything in the world, including determining who lives and dies by how much resources they use (carbon debt). With 2 high input/output countries, good luck on this happening either.
And we have to look at all the smaller ways to handle global warming. One proposal is to dump megatonnes of lime in the ocean?! Or perhaps this carbon credits scam: it makes the rich richer (Well, where DOES the money go?). At least sources of energy like solar or wind make sense... Until you realise the amount of energy to make a solar panel is greater than the total energy you will get out of it. Bummer.
And underlying is this assumption that global warming == CO2 peak.. I've heard of this law called thermodynamics. CO2 may trap heat, but heat generated anywhere is still heat. We generate heat via our vehicles, electric grid, generators, burn piles, and other human sources of heat. Is this not a direct consideration as well?
A little googling on solar panel energy cost found, for example, these links:
http://solarbus.org/documents/pvpayback.pdf
http://www.theoildrum.com/node/3910
which claim that energy payback of solar panels takes about three years.
For various reasons I think we'd do better with advanced nuclear, such as integral fast reactors or molten salt reactors. Either would be safer than what we have now, proliferation-resistant, and produce a lot less nuclear waste with a much shorter lifetime. We could have a very energy-rich future without carbon emissions.
As for carbon credits, a lot of economists advocate a "fee-and-dividend" scheme. Instead of trading credits, major source emitters simply pay a flat fee per ton of carbon, passing on the cost to the rest of us. The money is divided among all citizens, equal amount per person. Most people come out ahead (since the median emissions are less than the average), but since the dividend is constant and the new cost variable, everyone has more incentive to conserve.
I've seen calculations for the contribution of waste heat and it's very minor compared to greenhouse gases. However, if our energy usage continues to grow exponentially on this planet it'll be a real problem in a couple hundred years: http://physics.ucsd.edu/do-the-math/2011/07/galactic-scale-e...
For example, I'm in Australia. Aluminium smelting here consumes about 1/3 of the electrical energy produced. Mostly that's done with hugely subsidised brown coal. If there were a serious effort to use solar power to smelt Aluminium instead, you'd see a big reduction in the CO2 produced, and it'd likely be cheaper than the current situation.
But there isn't the political will to get it done - primarily because of idiotic arguments like yours.