>Adding electric motors and a battery to diesel trains JUST for carbon capture seems foolish.

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.

Direct air capture is the holy grail of climate solutions. Its success would offer us a way to put the cat back in the bag, and see CO2 levels decrease.

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.

Great. Now build out the infra… adding carbon to the air.

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”.

Unless you're in a sufficiently carbon dense region (third world maybe) it seems exceptionally optimistic to assume the train will be able to power more than itself in either scenario. Not that it's not a good idea anyway but unless the train can cover itself with spare change leftover you're not going to be powering anything extra without creating waste.

There might be an additional benefit for fossil fuel trains. Point source capture is usually more efficient than direct air 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.

Do trains always have a connection to the grid?

That's rather a lot of spelling braking as breaking to let pass without comment on a top post.

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

Or just go fully electric overhead like they do in northern european countries. Some of the ore trains in the far north generate a fair bit of electricity from regenerative braking that's then used by other trains going uphill or fed into the local power system.

Because the motion of the train would alleviate the need for large power consuming fans.

Trees capture carbon, but they don't sequester it. You need additional steps to prevent the biomass from decomposing. This isn't too hard, generally just burying plant material below enough earth will do the trick, but it's a substantial expense at scale.

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.

Photosynthesis is pretty inefficient and trees release the CO2 when they rot, so they aren’t great for long term storage. At certain phases of growth, forests are actually carbon positive. DAC can bind carbon to rock or pump it deep underground where it will stay potentially forever(on any meaningful human timescale). You can also directly account for the tons of CO2 removed by DAC which makes it more used for carbon trading schemes that financially incentivize capture.

I think the example to look at is biological nitrogen fixation, vs. the Haber-Bosch process, which operates at high pressures and temperatures and therefore has a small area footprint. You can do biological nitrogen fixation with legume (pea, bean) crops in symbiosis with nitrogen-fixing bacteria nodules, and then compost the crop to generate a nitrogen-rich fertilizer, but this means devoting large fields to the process. The Haber-Bosch process in contrast can produce much greater amounts of pure ammonia in a single location.

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.

you only can plant so much trees, with no guarantee that they even will grow old; currently we do everything but increase tree "population", because instead of going vegan we have ever rising meat consumption demanding more and more land for agriculture.

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

Because trees cannot be grown just anywhere, they require specific [land, water, nutrient] conditions that also happen to be the same things that are already under pressure from our civilisation. This is caused by things like extensive monocrop agriculture, grazing etc. Furthermore, trees do not necessarily sequester carbon beyond their lifespan - the sequestration is an additional process that may or may not occur naturally. Think of old trees dying, falling down and decomposing vs old trees dying and being covered by mud.

I read The Ministry for the Future recently and it was largely centered around the idea of a Carbon Coin (money based on how much carbon you sequestered or didn't emit). https://en.wikipedia.org/wiki/The_Ministry_for_the_Future

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

Totally agree, woody biomass is being under utilizes these days. Gasification produces syngas which can be used to produce heat and electricity when wind and solar aren't producing. The biochar that is left over can be introduced into the soil to improve it's nutrient and bio-activity (terrapreta). This is essentially reverse mining of carbon and is stable for thousands of years in the soil. It also keeps the biomass from producing greenhouse gases from decomposition.

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.

In much the same way that a solar panel is more efficient than a tree at capturing energy from the Sun.

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.

Considering that most of the energy supply is currently going into brake pads, designing an efficient regen braking system is quite reasonable.

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?"

Or at least create the hydrocarbons in a factory, sucking the carbon from the atmosphere, and using energy from renewable sources or something of the sort. This would be carbon neutral at least, and still allows liquid fuels to be used. I have never seen anybody invest into this research. Somebody please correct me if I'm mistaken here.

It's not either-or. Planting more trees is necessary but not sufficient.

> Are parts of the US unable to electrify trains for some reason?

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.

Not sure why AlgorithmicTime's comment is dead, so I'll reply here. Long distances are probably tricky to electrify. I don't know enough about US railroads (what little I know of US railroads comes from playing Ticket To Ride) to comment on the feasibility, but there are very long electrified railways in China and Japan, across difficult terrain. There is probably not much benefit in feeding electricity from regenerative braking back onto the overhead line if it's a very long segment with only one train (no one to use the power + transmission losses).

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.

Even if fully electrified train is difficult, hybrid and energy regeneration could be better.

Those ridiculously long distances in the middle of nowhere are not really well suited for overhead electrical wires.

Batteries are no-go. Typical electric locomotive is like 5MW sustained for multiple hours. It wouldn't be able to pull just its own batteries for any reasonable distance.

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