The key insight is that you don't need to turn carbon dioxide back into carbon. You just need to store those carbon atoms it in a stable form that keeps them out of the atmosphere. The most plausible way of doing that at large scale is to accelerate the reaction of naturally occurring silicates from rocks with atmospheric CO2.
"From a thermodynamic point of view, inorganic carbonates represent a lower energy state than CO2; hence the carbonation reaction is exothermic..."
That's from chapter 7 of the IPCC Special Report on Carbon Dioxide Capture and Storage, which I recommend reading for more details.
Chapter 7 PDF: https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...
Page 321 has the executive summary with your quote.
Parent page for full book: https://www.ipcc.ch/report/carbon-dioxide-capture-and-storag...
The gist is that if you look at the exponential curves of growth of both wind and solar deployments, and assume that we don't back off from those, you get X amount of TWh/year in 2040. Combine that with conversion of heating and transport to electrification, which provides huge efficiency boosts and requires only 1/3 to 1/4 the energy (most fossil fuel energy is just wasted). Then add in all the parts of the developing world which will increase their energy use to EU/China standards, and we are just barely there.
However I think we are likely to see big gains in production capacity as the developing world ups their game. They will be consuming more electricity, but also be immensely more productive.
It isn't, and it won't be. Carbon capture is a pleasing myth we tell ourselves to avoid the massive and immediate actions that would be necessary to avert catastrophe.
We're addicted to fossil fuels, telling ourselves that when we eventually sober up we can undo the damage we've done to ourselves.
There are several startups trying to come up with ways of sequestering atmospheric carbon in ways that will last for thousands of years. We need something like that to work, and to come up with ways to fund massive deployment in the second half of this century.
IMHO when estimating future, starting with the desired outcome (or even considering it much) is harmful, as it causes you to accept unrealistic assumptions and estimates for the key items driving your predictions, just so the predictions will come out as "acceptable" to you. You need to consider the impact factors as they are, and have realistic expectations of the effect and likelihood of interventions (especially considering the specific motivation factors of the narrow groups who can make each of those interventions, how that aligns with their interests), and see to what prognosis they lead you.
If we "need to come up with ways" then it means that it's plausible that we won't, and we (in this case, not we-as-the-world but we-as-individuals and we-as-smaller-communities) also need to plan on how to protect our interests in that (quite likely) scenario. An aching desire for something to work does not imply that it's possible in the required timeframe. Especially because there's no single "we"; those that need a solution to climate change and those that could fund it are largely separate groups; you can't look at it as a primarily technical problem when the largest impact factors are political.
Perhaps you can avoid "unburning" it by some other chemical process (which is why I was asking this) but simply pumping the CO2 somewhere does not seem a reasonable option, the only place on Earth that can easily hold that much of CO2 gas is the general atmosphere where it already resides.
Climeworks' proposal to pump it into basalt caverns, where it chemically reacts and becomes solid, is one way around that.
Carbon Engineering is doing gas to liquids, and claims that they need ~2.25 kWh of electricity to convert atmospheric CO2 to 1 kWh worth of liquid hydrocarbons. We will see.
We will need gigatons/year of sequestration in 2050. It's going to require a ton of innovation to get there.
We'd need to pay back all that energy, but in the coming decades we can't even afford the energy cost of the relatively much simpler solution of "simply" not burning bulk carbon for heat.
Re gas heating, I sure could've used some just this past winter during the Texas snowpocalypse. My apartment uses electric power for heating/cooking, so electricity was a single point of failure. Resiliency through diversity is a point I missed above.
In essence, we're still burning lots and lots of carbon just to extract energy. Thermodynamics says to reverse the process and get carbon from CO2 we need to put all that energy back, with a hefty bonus due to inefficiencies.
So how can it be feasible to afford enough energy to "unburn" a century's worth of burnt carbon if we can't even get enough energy to avoid burning new carbon in the first place? Like, our energy generation might double in a few decades, but this "unburning" would require so much spare energy that it doesn't seem likely to achieve as soon as the second half of this century.