I think your point misses part of the market's intent. If you want the market to act correctly, you have to model the carbon or greenhouse constraint in the opmization.

That way you'll send the proper price signals and incentivize new generation or other assets (badly needed in much of the US). What we're currently doing fixes one problem and causes another. This is why ERCOT is having to do things like add in a $9000/MWh ORDC (among other reasons). The prices are just too low.