I really don't understand how carbon capture can make sense, in terms of thermodynamics. Burning hydrocarbons releases energy, plus carbon dioxide and water vapor. Capturing the carbon dioxide back would, in some way, require an equivalent amount of energy to be spent, right? Where is this energy coming from? In this case, it's actually mentioned in the article (unlike many other carbon capture proposals): add regenerative braking to trains -- plus make the engines work harder by adding a lot of extra air resistance for the filtering system.
Meanwhile, the European electric grid -- and therefore its electric trains -- is partly ran by burning fossil fuels (not to mention the manufacturing processes for the proposed batteries and filters). So you're burning carbon in order to get carbon out of the atmosphere -- there's no way that equation comes out as a net negative for emissions, there are inefficiencies everywhere.
This is honestly one of the most compelling carbon capture proposals I have read, and it still doesn't make sense to me. What am I missing here? Why is this being taken seriously?
Artificial photosynthesis is absolutely required in several sectors, if you want to eliminate the use of fossil fuels. International air travel is the main example, so is space travel, and global shipping is a little behind. There's no way to fly passenger jets over the Atlantic and Pacific Ocean using battery power; the density is just too low. Likewise, if you want to have SpaceX continue to launch large methane-fueled or RP-1 fueled rockets without fossil fuels, capture of atmospheric CO2 and conversion to hydrocarbon fuel will be needed.
It's also a way of storing energy for long periods of time, i.e. if you're in the near pole regions of a planet, and want to capture solar energy in the summer and use it in the winter, batteries aren't going to work on those timescales. Some other means, generally a stable chemical conversion, will be needed. Converting carbon dioxide to methane or gasoline, converting nitrogen to ammonia (a bit dirty), even converting iron oxide to reduced iron, are all possible methods of doing this.
As far as converting atmospheric carbon dioxide to a form that won't eventually get back in the atmosphere, that's pretty difficult (you have to make limestone, CaCO3, or perhaps carbon fiber building materials, or even better, diamond).
I'm not against that point, as I mentioned in another comment, research into hydrocarbon synthesis is the only "carbon capture" scheme that makes sense to me, because it's not promising anything for free. "We'll use this solar/wind/nuclear energy to create fuels out of the air, and then we'll burn them later for less" makes thermodynamic sense, and as you pointed out, is necessary to continue some endeavors (and maybe to permanently remove CO2 from the atmosphere, at a huge cost).
It's these "we'll use fossil fuel energy to pull carbon out of the atmosphere and store it" schemes that smell like perpetual motion machine trickery to me.
And you are right... even worse: putting carbon emitted back into the ground requires not only the energy gained through burning, but several multitudes of that.
That's why not burning it in the first place is almost always better. Still, carbon capture is necessary, because there are things that are extremely hard to substitute.
Further, if we don't go for negative emissions, we will have at least 4 degrees of warming (even if we stop emitting now).
Meanwhile, the European electric grid -- and therefore its electric trains -- is partly ran by burning fossil fuels (not to mention the manufacturing processes for the proposed batteries and filters). So you're burning carbon in order to get carbon out of the atmosphere -- there's no way that equation comes out as a net negative for emissions, there are inefficiencies everywhere.
This is honestly one of the most compelling carbon capture proposals I have read, and it still doesn't make sense to me. What am I missing here? Why is this being taken seriously?