My point is that in achieving the goal of zero or negative net carbon emissions, changing the economic price structure which allows carbon emissions may prove to be an effective tool. It's not that the market solves all problems (something with which I strongly disagree), or that an unregulated market is the only option (a view I reject absolutely as absolutely false, blatantly ahistorical, and a complete misrepresentation of market theory). But markets are powerful.
At a sufficiently high level, and in the case of a carbon tax, that's likely to be exceedingly painful, the option to emit simply doesn't exist.
Bake that price structure, through both depletion amortisation (a much stronger update to Hotelling's Rule, which was based on multiple false premises), and an at-the-source sequestered carbon introduction tax, at all levels of international banking, finance, and trade, and you make it a money-losing proposition to mine coal, pump petroleum, or drill natural gas, anywhere.
When I say that the taxes would be painful, I mean increasing costs not by a few percent, but by orders of magnitude. That's going to be heavily traumatic -- it's a large part of what's exploded social unrest across the Middle East in the past five years, and is in the process of tearing Venezuela to shreds. Saudi Arabia and Russia are likely next on the block even if only present trends continue.
So yes: the carbon tax would be an outright ban, though it might take some time (~10-20 years) to fully reach that stage. I'd prefer faster. Hell, I'd prefer we'd taken this approach in 1960 when the consequences were first becoming apparent.
Infrastructure and capital take time to replace. We're looking at rebuilding an airplane in flight. I'm not at all sanguine that we'll succeed.
And: if we do address the CO2 problem, there remain numerous others, most reducing to total population and absolute average wealth (which is to say, resource consumption). Which are likely to destroy what we call modern civilisation even if we do manage the carbon crisis.
Putting those first: what we need isn't more time, or an energy miracle. It's to embrace limits, the fundamental limits of Earth's carrying capacity, and how many people, of a given material affluence, can be supported. This is a question I've been looking at for the past several years, or more accurately, I've spent much of that time trying to figure out what the fundamental question was, starting from "what are the big problems?" My answer:
How do we embrace limits to growth?
Gates raises a few really excellent points.
He dismisses the problem of not having a price on carbon. I'd return that not only is that a problem, but we've a much larger issue of not fully accounting for the creation or replacement price of the fossil fuels we've been consuming at a breakneck rate -- some 5 million years of petroleum accumulation are consumed every year. That itself is an accident and error of early economic theory (one which was very nearly corrected in the late 19th century), and of early theories, and derived law, of mineral rights law (look up the "rule of capture" for a few hours of entertainment).
His mini-biographies on Parsons and Deisel, collectively the two people who now power much of the world, was a telling rebuttal to the claim that capitalism rewards innovation. Neither man made much from their inventions, Deisel, as Gates says, committed suicide in the face of bankruptcy.
On the storage front, there is one possiblity that's open to us: liquid hydrocarbons. They're not a net energy gain, but if we're looking for a storage solution that's high-density, highly flexible, and has very long-term proven storage life (100 million years and counting), electrically-generated synfuels offer a plausible pathway. Specifically seawater-based Fischer-Tropsch fuel synthesis, studied for over 50 years by Brookhaven National Labs, M.I.T., and the US Naval Research Lab. There are undoubtedly complications, but it's an underconsidered option.
Also on the storage front, the Dr. Sadoway mentioned is one of the recent superstars in battery storage technology. His molten salt battery isn't something you'd want to put in a car, but with extremely abundant (cheap!) substrates, could form the basis of city-scale electrical storage. Not for hundreds of millions of years, but days to weeks, evening out supply inconsistancies for a grid dependent on intermittent renewables. The fact that this technology is facing obstacles is disheartening. It's also why I advocate both considering sustainable, carbon-neutral paths to liquid hydrocarbon fuels, and embracing limits.