Future trains could provide carbon capture

This isn't necessarily directly point source, but if the diesel exhaust is partially directed into the capture train, the CO2 concentration should be higher, and could have a more efficient CO2 capture.

The problem is how absurdly expensive these things are. In the next couple decades, even being optimistic, it's hard to forsee a scenario where we've plugged enough holes in our infrastructure that direct air capture will be better or cheaper than doing more capture inside some existing pollution site, or replacing more fossil fuels with clean energy.

But one day we will reach that point. And when we reach that point, anything to reduce the cost of carbon capture a little bit will help a lot.

So yes, regenerative breaking connection is sort of a distraction. But improvements to DAC efficiency are very welcome, and improving airflow by mounting the mechanism on a high-speed train seems like it offers a big improvement.

The state of things leave little wiggle room for iterating on and disposing of one experiment after another

Reducing consumption and industrial activity is a sure fire way to reduce carbon in the air

But I expect we’ll avoid intentional figurative death for adults today and chuck the risk over the fence into the future as usual, given how people behaved when lockdown meant “no haircuts”.

I know this is very nearly content-free. Forgive me, it's a compulsion.

There's no such thing as a train propelled by a diesel engine.

All "diesel trains" are diesel-electric. They use electric motors for propulsion, and for braking as well. Normally, there's a big resistive grid on the roof where the power is dumped.

Even restoring all the forests that have existed pre the industrialization will not help much, because it only resets a small part of the emissions. All fossil fuel burned is still in the atmosphere, likewise increasingly more methane.

Additionally, it's easily used for green washing.

Plant trees -> Yai carbon is offset, can emit like before; then trees are cut down, burn or don't even grow, and the next company can plant trees at the same land

Haber-Bosch traditionally has relied on large fossil fuel inputs, but it's possible to get the hydrogen from the process via hydrolysis of water, powered by renewable energy (or nuclear), and use electricity instead of fossil fuels to run the high-temperature, high-pressure catalytic reaction (H2 + N2 -> NH3).

The same arguments apply to carbon capture and fixation: you can do it in an industrial setting, for example the North African desert (which doesn't support much plant growth), you could use seawater as the hydrogen source and plentiful sunlight and PV/concentrated thermal for electricity to drive the carbon capture (fans etc.) and the analogous version of Haber-Bosch (Fischer-Tropsch) for CO2 - CO + H2 -> hydrocarbons.

Would be interesting to try it IRL, as you'd potentially have lots of different approaches being tried vs some kind of top down solutions

And scale is really the issue. All the world's forests combined currently absorb about 20% of CO2 humans currently emit. To go neutral, you're looking at planting around 12 trillion trees. Worse still, about 30% of Earth's land surface area are already covered by forests, so you can't simply expand the forests to get the required carbon capture.

The only realistic way to achieve 100% carbon capture by biological means would be to seed algae blooms in the ocean, which for short term carbon uptake would work pretty well, but when that algae dies it is way harder to prevent it from decomposing, meaning you don't get long term sequestration. Further, you are talking about terraforming-level changes to marine environments all over the world. Beyond the catastrophic effects that can have on other species, the full effects of what that might do to us are impossible to fully predict.

Artificial carbon capture might have higher capital costs since the equipment is not self replicating, but it can be orders of magnitude more efficient in terms of energy, CO2 capture rate, and land use requirement.

Once we are on renewable energy, the efficiency argument will make it undeniably efficient.

This drought is teaching us that "just grow a tree" is not always viable, and the resulting water crisis is also begging the question "with who's water?"

Beyond trees, we should also be growing algae and other plant mater to sequester more carbon and produce oils, sugars and other useful ingredients for our lives. This can be done at sea or in areas where water is scarce and normal vegetation grows poorly.

Or a jet is more efficient than a blackpoll warbler at migrating across the Atlantic.

Or a knife is more effective than a claw at cutting through things.

In a world full of examples, why should carbon capture be any different?

Trees weren't designed to capture carbon, so there's every reason to think something which is can do a better job.

It basically comes down to cost. The electric infrastructure costs per mile to install, and per mile per year to maintain. The benefits come per train. If you don't have enough trains per day, it's not economical to electrify.

There are some places, like the Union Pacific around North Platte, where you'd think that electrification would be a natural. But the problem is that 90 miles east of North Platte, and 20 miles west of North Platte, the lines split, and the traffic density goes down. Switching between electric and diesel locomotives twice in 110 miles adds operating cost.

I wonder at which point diesel becomes the cleaner option here, if ever. One the one hand, you have to lug a lot of fuel around over longer distances (or you need refueling infrastructure). On the other hand, transmission losses can be significant.

60 miles of catenary is way cheaper than wasting energy pulling dead weight that batteries are.

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).

Just watch out for greenwashing

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).

In fact i'm not sure why that wouldn't also apply to the trains...

For the rest, they don't because of lack of storage.

A diesel locomotive has a huge engine block, a generator, a large radiator, and electric motors on the axles. You can turn the motors into generators when you want braking, but where are you going to put the electricity? All the space (and weight) is already used.

Yes, they have batteries - enough to crank the engine when it has been turned off. Not enough to run the electric motors on the wheels, though.

If you don't have a grid as "storage", you need to carry it, and that's a problem. And freight trains obviously only have motors in the locomotive(s) and do the distributed braking on the cars mechanically, so a good chunk is lost even if the locomotive can do it.