I’m seeking reader input to the headline question.
Rich countries like the U.S. need to cut CO2 emissions more than 80% by 2050 to have a serious shot at the 2°C (3.6° F) target climate scientists say is needed to avoid the most dangerous climate impacts and potentially irreversible tipping points (see “Study Confirms Optimal Climate Strategy: Deploy, Deploy, Deploy, Research and Develop, Deploy, Deploy, Deploy“). Here’s the key chart from the IPCC’s full Working Group III report (Box 13.7, page 776):
I’d like to put together a picture of the U.S. in 2050 if we met the target — but just the “modest” target from the 2009 climate and clean energy jobs bill of an 80% reduction compared to 2005 levels.
Certain questions need answering. How much total energy is consumed in 2050, which is to say how much energy efficiency and conservation has been achieved — they aren’t the same thing. Certainly by 2030 (if not sooner), we’re going to be quite desperate to avert Dust-Bowlification and irreversible loss of the great ice sheets, so in the 2030s and 2040s one can imagine a considerable amount of conservation and dematerialization separate from the technologically-driven energy efficiency that is possible. [No, I'm not interested in scenarios of economic/societal collapse. That's avoidable if we act, but it is certainly in play if we don't.]
How much coal, oil, and natural gas is being consumed (with carbon capture and storage of some coal and gas if you want to consider that)? What’s the price of oil? How much of our power is provided by nuclear power? How much by solar PV and how much by concentrated solar thermal? How much from wind power? How much from biomass? How much from other forms of renewable energy?
What is the vehicle fleet like? How much electric? How much next-generation biofuels? What about the rest of transportation, including air travel? If you want to waste time throwing in some hydrogen cars, I suppose that is your right, but it remains too expensive and implausible to be a major, cost-effective carbon-saver even in 2050.
Please, also, feel free to identify links to analyses that have already done part or all of this. Again, I’m just looking for the U.S. energy mix.