> NOTHING we will right now will have ANY significant effect in less than 100+ years

Where are you getting this from? Some people are estimating the lag to the maximum effect as low as ~10 years [1], with the popular consensus being ~30 years until the peak effects are reached (so probably a lot less time needed for any significant effects to be felt). If the 100+ years were true, it's very unlikely we'd be able to measure any large effects from emissions from 100+ years ago, while the average temperature have increased by 1°C [2]. In that time cumulative emissions have increased 16-fold (1920: 100 bT, 2020: 1.6 tT) so we'd be fucked without any recourse if that were true.

That seems to be a sorry excuse to just say "fuck it, we'll just have to adapt when the time comes"

The broad scientific consensus (ipcc) is that just continuing on like we do right now will have significant detrimental effects on humanity and that actions taking today can stop global warming by ~2040 [5].

> beside the fact that in environmental terms are no more friendly than a plane

Where are you getting this from? Or are you conflating environmental impact in general and global warming impact specifically for this argument? (Which I'd also not agree with, but that's a different point).

And why would cities be less able to adapt? They seem to be better suited for adapting, with more indoor spaces and less energy & resource usage. Due to the concentrated nature a lot less area has to be adapted for climate change effects (and there certainly are cities that won't exist, primarily due to sea level rise, but that's also the case for non-cities).

Air travel especially suffers from noise & pollution (not the co2 kind) concerns, which is (at least in europe) stopping many airports from expanding. It's also very limited in capacity.

Water has great capacity, but can only use few fixed waterways, with most inland waterways requiring a significant amount of human intervention to make them suitable. Why would a ship be more flexible in travel & destination than a railroad or trucks?

I also disagree with your hypothesis about the needed flexibility on most infrastructure projects in regards to time. Most railways & highways are by now more than 40 years old (with railways usually being much older) and very few parts have been deemed useless (at least in germany), because human development is pretty fixed in place, with most population centers 40 years age still having at least a significant population now. Usually the worst issue is that capacity is quickly reached in just a few years, but that's more of a nice problem to have.

Climate change will have effects on human living, but if we let it get so extreme that formerly unlivable places in the north become very livable while those built up areas that are currently used by humans become unlivable, I doubt a functional global or large distance transport network will be available or even necessary on a larger scale.

And regarding the Green New Deal: Recommendations from it[3] seems to outline needed actions for emissions cuts and approaches for mitigating climate change[4] in the near term pretty well.

[1]: https://iopscience.iop.org/article/10.1088/1748-9326/9/12/12...
[2]: https://www.climate.gov/news-features/understanding-climate/...
[3]: https://en.wikipedia.org/wiki/Green_New_Deal#Green_New_Deal_...
[4]: https://www.ipcc.ch/site/assets/uploads/2018/02/AR5_SYR_FINA... P. 27
[5]: https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6... P 15, P 18