If you correctly price in the negative externalities of burning gasoline, then the suburbs suddenly get a lot more expensive, and it makes more sense to densify.
In practical terms, in five years or so it's not going to be hard to get people to buy electric cars instead of gasoline, but it will still be practically impossible to get them to give up their houses, back yards, and cars to go live in the city.
Then they get all the benefits of conservation without being poorer, while particularly punishing those that don’t rearrange their lifestyles.
If the goal is to continue to survive as a species, there are much more effective strategies to implement.
Suburban living on average doubles the climate impact of the same number of people in a city. The OP notes correctly that this externality is not correctly priced in the current market.
You also haven't considered that as you move people into cities you need to scale up infrastructure in the city itself. Living spaces, transportation around the city, supply lines for supermarkets. Everything needs to scale. It's not black and white that moving everyone into a tightly packed city is going to make a meaningful difference to global emissions.
What would make a tremendous difference is turning the entire grid into a green smart grid powered by solar, wind, geothermal, etc. That would change things regardless of where people live, because the sources of energy are decentralized and can exist basically anywhere that natural resources like solar and wind exist.
Carbon emissions are directly correlated.
> You also haven't considered that as you move people into cities you need to scale up infrastructure in the city itself.
Infrastructure has economies of scale, so environmental costs scale sublinearly with capacity.
The common answer is to not calculate it but to add a carbon tax. If you make gas more expensive, road taxes higher and non-renewable energy higher cost, the market actors will change their behavior.
As for the infrastructure cost, you pay that in either case and it’s more efficiently built the denser things are.
Simply moving cargo, the lifeblood of our economy, across the oceans burns hundreds of tons of fuel oil - releasing more (and more varied) pollutants into the atmosphere and oceans. One ship, by some reports, emits as many emissions as some 50 million (or more) cars. And there are well over 9,000 on the ocean.
https://www.nbcnews.com/mach/science/zeppelins-stopped-flyin...
> As proposed in a recent scientific paper, the new airships would be 10 times bigger than the 800-foot Hindenburg — more than five times as long as the Empire State Building is tall
Cargo ships pollute more SO2 and NO2 than personal automobiles. Those two gases cause acid rain. Acid rain is a problem, yes.
They pollute a lot less CO2, though, which is the gas that is actually going to kill us if we don't stop emitting it at the rates we emit it today.
A cargo ship is the most efficient form of transport, in terms of CO2/kg/km.
A personal automobile is the least efficient.
from the Global Climate Action Summit 2018, convened by CA Gov Jerry Brown:
Every 5 weeks, China adds a fleet of electric buses equivalent to the entire London bus fleet – 9500 buses. Technologies are now market ready, societally acceptable and economically attractive to reduce greenhouse gas emissions from transport by 51% by 2030, through electric vehicles, mass transit and adapting the global shipping fleet. A complete global and technological shift to electric vehicles now looks very likely and, given recent announcements from cities, countries and car manufacturers, is possible between 2020 and 2030. However, the transformation will slow dramatically without strong national and city policies, for example setting target dates to ban internal combustion engines.