Can we rely primarily on energy efficiencies in the meantime? Up to a point, yes; but efficiencies are not a panacea for all our energy problems. Energy efficiencies are known to cause rebounds, which can reduce potential energy savings by stimulating additional energy use.This is Jevons Paradox, and you can see it in gasoline consumption in the US over decades.
Here's a back of the envelope calculation:
Take CO2 and population data from the World Bank, for 2009. Assume that
- OECD countries cut their per-capita CO2 emissions by 30%.
- the per-capita emissions of the non-OECD countries reach a factor F of the OECD countries (currently F=0.29).
- the world's population increases to 10 billion, with all the increase in the non-OECD countries.
In other words, even if we cut our emissions by 30% and everyone in the world attains this standard of living, emissions would be 2.5 times today's.
You can't even get to today's (already unacceptable) levels of emissions, and F=1, unless the cutback = 72%
I don't see how you can possibly get enough cutback in emissions with conservation and increased efficiency, unless most of the world stays poor. The demographics swamp everything.
And if we have to reduce emissions by 80% of today's, it's impossible without new technologies (at least in energy storage, if not renewable energy). Impossible. You can't even get close.
You must either (1) invent new ways to store energy, or (2) new ways to generate noncarbon energy. Lots of it, on demand. R&D is the only answer.
Note: the only data I used is (2009):
OECD population: 1.225 B
non-OECD population: 5.536 B
OECD per-capita emissions: 9.83 mt
non-OECD per-capita emissions: 2.88 mt
(Remember, US per-capita emissions in 2009 were 16.9 mt.)