We're more in agreement than disagreement. And I'm largely not contesting your assertion that these are challenges. The question is what, if any, alternatives or mitigations are available.

I don't think we're close to solving the problems. But there are domains which look more promising. We can at least look to exploiting those (which means spreading awareness), whilst addressing others, and cutting a huge intractable problem into smaller ... yes, still often only very-barely tractable ... problems.

You might care to adopt a less confrontational attitude.

There's also the distinction between remaing at the present level of ~37 gigatons CO2 (increasing at 1.6% per year, or doubling every 43 years), to far nearer 0 in terms of gross, and what potential there is for then making up that difference.

My preferred carbon capture technologies are wetlands and trees, in about that order, for the record.

On rail: of transport modes, only water is more efficient, and that just. Before rail, canal or river conveyance was your best bet, and that still carries tremendous amounts of cargo, with high bandwidth but low latency.

All told, the embedded energy of rail is comparatively low, especially relative to paved roads (asphalt). It's pretty hard to do better. Let's not toss this one out.

Shipping: again, it's not carbon-neutral, but the most effective use of what carbon we're using, with mitigations elsewhere, if possible. The point being that there is far more fuel flexibility than in flight.

Indoor climate control: Again, the question remains, what's possible. Passive designs, which in many cases aren't high-tech, but traditional, can achieve. At the very least, directly addressing heating and cooling via passive, thermal storage, and circulation methods makes the remaining humidity / moisture concerns more tractable.

Materials: The larger point here is that changing costs (financial, internalised ecological, energy) will change materials and land use, and building practices. Skyscrapers are ... useful in some regards, but with light to increasing urban densities, there's a lot of mileage in low-rise construction (5-10 storeys), which traditional materials are well capable of, and which achieve densities that only a very few high-rise cities presently match.

Ag: numbers I have say 13% of total emissions:

https://www.wri.org/blog/2014/05/everything-you-need-know-ab...

A large fraction of which is livestock (I'd listed nitrogen fertiliser, which I still believe is the largest fossil fuel input). Thankfully, methane's residency in the atmosphere is far shorter than CO2's, though it's a much more powerful greenhouse gas. Global livestock biomass is truly immense, both absolutely and by historical standards:

http://peakoilbarrel.com/wp-content/uploads/2016/01/Terrestr...

https://xkcd.com/1338/

Genetic engineering of crops may be possible, but we've already transferred a great deal of agricultural primary productivity from survival to caloric activity through the Green Revolution and hybridisation. How much potential remains is ... an interesting question. (See especially Ophuls's ecology texts.)

For heating/cooling, the low-hanging fruit are passive designs, additional insulation, thermal mass, site-appropriate design, limited footprint, limited exposure, increased ventilation in warmer climates especially, as well as district heating / cooling. These can achieve tremendous efficiencies over existing heating/cooling loads.

Again, reading to point: the solvable portion of the problem makes the less-solvable moisture/humidity management at least more tractable.

Smil: He'll be the first to tell you that he doesn't have all the answers, and that BAU isn't sustainable. But he'll do so with copious amounts of extensively-researched, detailed, and soberly-presented facts, addressing much or all of the relevant aspects of the domain. He doesn't just throw his hands up in the air (at least not in public), or castigate his counterparties.

Like Smil, I'm not an optimist. I am a realist, however, which means making realistic assessments of the situation and possible future(s).

Most of those possible futures don't look so hot, frankly. This is like threading a needle, and the tolerances are low.