Redesign cities such that people can safely get around by bicycle.

“This will be the hardest because unless the vast majority of power is supplied by something else it will drag humanity back into the pre-digital age” Not really. Consuming a lot less (no new car every 3 years, no big buildings, a lot less junk in general), wasting a lot less (no bitcoins, no ads, a lot less A/C and heating) etc. would already achieve a lot. Probably to the point that powering with renewables (+nuclear) would be feasible.

"-12,800 megatons / year" - hope we can save some for cows then, like cows. basically total says - go nuclear and things are done. definitely a much better answer than those before, that's for sure.

Honest question: how long till we deplete the raw material for nuclear energy?

Note that economically nuclear loses out to renewables with present day technology. If you want to build up new electricity generation capacity it is much cheaper to build wind turbines and solar power plants (that is still true if you build your solar power in cold europe instead of the middle east). Nuclear is just way too expensive to make it a useful solution.

"Once lab-grown meat becomes commercially viable" - I don't know about lab-grown meat specifically, but I'm sure meat alternatives in general are already commercially viable. The only potential practical limitation I see on just banning meat altogether today (if you ignore the risk of people whining) would be how quickly meat alternatives can ramp up their production to meet meat demand (but even this may not be as big of a problem as it seems, as I've heard what we're feeding animals would already be enough to sustain humans).

RE: your points 1 & 2: I think your global impact estimate is way too high. This source says that the US has relatively shorter commute times, largely due to higher proportion of public transit use in other countries. I'd also bet that in Europe and parts of Asia fuel efficiency is higher for commuter vehicles then the US, on average.

Some quick googling suggest that in US 5% of commuters use public transit, in Germany it's 28%. In India, accounting for nearly 20% of world population 66% walk, bicycle, or don't commute, 18% use public transit, 13% use mopeds/motorcycles, and only 3% drive, so eliminating cars will have almost no effect. I'd expect China to be not quite as extreme but similar.

@quarague cheap solutions is what got us there in the first place. solar panels rob plants for place to absorb stuff, lol, including those on the roofs.

You have ignored the energy cost of creating the infrastructure to make your estimates possible. For example, 400m commuters using public transport with 40 per bus: assuming one bus can make 10 useful commuter journeys at each end of each working day, that requires building 1m buses, and in a country like the USA where the road infrastructure has been left to rot for half a century, a lot of new road construction - and more expensively, bridge construction. (Buses are heavier than cars, and therefore damage roads faster than cars).

@quarague, renewables only work right now because natural gas makes up such a large part of the energy mix: if a cloud passes over a solar array, or the wind dies down, you can fire up a gas turbine or two to compensate. Going pure renewables requires an extensive storage infrastructure to compensate; going nuclear doesn't.

@alephzero the savings are net - considering that you'd have to sink enough money into the roads to keep car commuting from urban sprawl suburbs a viable option. If even a fraction of the money that currently goes towards buying and maintaining cars and the roads they drive on were to be reinvested in public transports like trains, trams, subways & buses this is a clear win.

@GregorThomas if the 4.8 ton / car average cited by DoT is right it's going to be somewhere in that category. Results will vary depending on how many cars are used in a given country. Feel free to check my math though

@Ivana very good question I would be curious to know that myself.

Vincent comment is rigth about calculations. Source of mistake is that electricity is about 1/6 of total energy(if I remember it correctly), take look at wiki total energy consumption world wide for exact number. So, it will require more nuclear reactors. Which require then full cycle of fuel and fast neutron reactors which will be breeders. We are close to have it, so not a big deal. Modular reactors yeah good stuff.

@AdamCoville I think the 4.8 ton / car is probably right for the fleet of American cars being driven the amount that Americans drive them, on average. I think if you look at the global fleet of cars - both more fuel efficient and (more importantly) driven less than American cars, I bet that number is lower by at least 20% - let's say 4 ton / car.

Bigger is your reduction based on the 2B global workforce assumes that all 2B are commuting by car to start. In reality, at least 70% of the world population in countries like China, India, Indonesia, Pakistan, Brazil, Bangladesh, etc., have a commuter profile similar to India - say 5% of the workforce drives. A rough estimate of the number of commuting drivers is something like 5% drivers * 70% * 2B workforce = 70M cars, plus 80% drivers * 30% * 2B workforce = 480M cars = 550M cars total. Let's say 50% of them can go remote = 275M cars * 4 tons CO2 = 1.1 megatons CO2 reduction.

So a better estimate is about 80% lower. Since point #2 is based on the same assumption, it should probably also be ~80% lower, so 400 megatons of CO2. I would make the summary remote work: 1.1 megatons, additional public transit: 400 megatons. And all of a sudden lab grown meat / reduction of meat in diets looks like much higher impact globally.

It's really just a handful of egregiously bad countries (ahem, USA), that need to change their car culture and invest more heavily in public transit to have a big current impact. Investments in public transit in developing and growing countries is important too to keep them on the right track.

Indeed. And our regulators / city planners deliberately axe public transport as a way to drive car sales and make manufacturers happy. It's really a toxic situation. I wonder if military intervention wouldn't be what is really required