The problem is the carbon dioxide that we need to make that much energy from now to 2056. In order to stop/stabilize our carbon production we need to reduce carbon dioxide by 175 billion tons of C02.
This is seven stabilization wedges of 25 billion tons each. It is useful to think of these wedges since we can use different means to make achieve each wedge. Each wedge reduction would make a significant impact.
Eight wedges might be
1. Carbon sequestering
2. Double nuclear power
3. Change cars from an average of 30mpg to 60mpg
4. 40 times our current wind power
5. 1000 times our current solar power - reducing need for coal plants
6/7. More energy efficient buildings, industry
8. A lot of biofuels
Reduce carbon usage to stay within a budget of allowable carbon to not increase temperature by more than 2 degrees. The US would have a smaller carbon budget than the global budget and smaller wedges.
You could depend on one of the approaches to take care of more of the carbon but it would be faster, more pragmatic and more practical to scale up several approaches at the same time.
A terawatt--one million megawatts--of "carbon-free" power is the scale needed to make a significant dent in projected carbon dioxide emissions at midcentury. In the terms used by Socolow and Pacala, that contribution would correspond to one to two of the seven required "stabilization wedges." Reaching a terawatt of nuclear power by 2050 is certainly challenging, requiring deployment of about 2,000 megawatts a month. A capital investment of $2 trillion over several decades is called for, and power plant cost reduction, nuclear waste management and a proliferation-resistant international fuel cycle regime must all be addressed aggressively over the next decade or so.