The literal footprint of a rail system is also very large; clearing and grading rail lines across the country would have a significant environmental impact.
citation needed. It helps a lot that (electric) trains do not need to carry their own fuel. Also, trains can run on low-carbon energy, whereas there is no viable alternative to jet fuel at the moment, and producing that from net-zero-carbon processes (akin to biodiesel) is not economical.
* trains are long
* trains travel slower than airplanes, and drag is proportional to the square of speed
* making conclusions solely based drag coefficients from the density of the air is sound reasoning
One of these statements is false. I get that hackernews is just a forum for casual discussion of various technical topics, but overly categorical statements based on a reasoning in a vacuum (no pun in intended) just force the conversation into unproductive threads like this one. I'm kinda sorry I took the bait at this point.
I hear this sentiment a lot, and I don't understand it. Trying to speak the truth isn't just optional outside formal contexts. There's no situation so casual that I it suddenly becomes appropriate to make up bullshit and present it as facts.
That is to say, I agree with your larger point: if nickff wants to make the claim that trains consume more energy than aircraft, he'd better come up with a reasonable source for that information.
I think if you want to make this analysis come out you need to include starting/stopping losses (and maybe fuel hauling, empty car overhead, etc...) to the train trip or somesuch. Naively trains are going to win and it's not even close.
* Transportation infrastructure is a societal investment that produces benefits, it's not just about its cost. Investing in terrestrial transportation like trains, even if it is more expensive can give rise to proportionally greater societal benefits than air travel--think, a long-haul train has multiple stops, providing connection points for economic activity (smaller towns and cities connected through train stations) that planes clearly cannot. I actually think it's totally OK that trains require more investment because they may create larger network effects in the big picture.
* In some sense, all societal spending is make-work. If we're going to have make-work programs, we might as well spend it on the best long-term strategy, which in my honest opinion, having lived in Europe for a number of years, is cities being well-connected with cheap and fast rail, subways, and trams.
* Climate change is a real thing, and it's due mostly to CO2 emissions. It's gonna cost money to fix. We need to stop deploying the "but itz mah dollarzzzes" as an excuse not to act. We need to start thinking about paying back the absolutely massive debt we racked up from cheap and easy energy.
* Carbon offsets are a shell game that we can play in the short run, but ultimate we need to get to zero carbon footprint, which cannot be accomplished with offsets alone.
In summary, we better start paying up.
https://www.grc.nasa.gov/www/k-12/airplane/drageq.html for the drag side.
There are also a huge number of fuel consumption, economic analysis, and environmental impact studies, but I am sure you can find those easily if you're interested.
This will not be any different nationally. It might actually be quite worse.
A plane is about 5 tons an hour, or 10kg per 300 people per mile, so 30kg of jet fuel per 1000 people per mile, or 1.2GJ
So a cruising a330 uses about 10 times the energy per passenger mile as an ICE high speed train.
Clearly the comparison of polution caused it then affected by how green the electricity source is and the extra environmental impact of burning fuel in the high atmosphere.