Future Transport and Energy - Cars, Trains, Ships and Planes
Cars are going to be non-carbon emitting in the future, but they cannot be expected to reduce pollution as BEVs (Battery-Electric Vehicles) since that just takes electricity from carbon-emitting powergrids. Moreover literally anyone that has briefly looked into how batteries are manufactured knows that they're as bad if not worse for the environment to manufacture as making gasoline and diesel. You are going to use your feet and public transportation more in the future so cars are going to be more need-based and not vanity items. The methods to do this already exist for Light Transport, the problem is how to decarbonize trucks, airplanes and ships. 71% of all carbon emissions are caused by 100 corporate enterprises (that do little to nothing to reduce their carbon footprints despite being able to nullify the majority of their outputs). There is no need to completely electrify transportation using batteries. Batteries make sense for personal cars, small trucks, and city buses. Trains don't need batteries since they can use overhead powerlines and live rails. Ships and aircraft cannot rely on batteries. They need fuel with far more energy density.
The go-to choice for Airplanes because power to weight of hydrogen is better than that of jet fuel. Fuel cells + electric motors have better efficiency (70-80%) than pure jet turbines (20-30%). Electric jets can still have a sort of afterburner that burns hydrogen for extra thrust.
Blended wing / Flying Body fuselage designs (a la the Su-27 or ЭКИП*) will accommodate bulky hydrogen tanks without much problems or downsides. Hydrogen will also be very interesting for heavy industrial vehicles, because all your industrial equipment now can produce a lot of electrical power, that can be used by secondary equipment. A big hydrogen powered tractor can probably double as an electric emergency generator for an entire town and power it for like a week. Cities could probably get emergency power out of H2 powered utility vehicles as well. And you can make hydrogen with a relatively small hydrolysis machine if you have water and electricity, which means it's possible to operate this in places where a traditional diesel supply is not viable. When most light weight vehicles change to electric batteries it might be cheaper to operate a hydrogen supply system for heavy equipment than a traditional fuel supply line. https://web.archive.org/web/20200709130123/http://researchbank.rmit.edu.au/view/rmit:20100/n2006040078.pdf https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft
The problem with hydrogen is that its cost intensive to transport, store and use. Here is the need for synthetic fuels: Using chemical processes to produce large quantities of molecules of diesel, kerosene, petrol etc.. There exists a process called Fischer-Torpsch which does just that.
The Fischer-Torpsch process requires hydrogen as an input so you could argue if you need hydrogen, why not just produce hydrogen fuel cells. The reason is that Hydrogen (Protium, Dueterium and Tritium) requires a large-scale production of new machinery and infrastructure, synthetic fuels do not. https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process
Alternatively Pyrolysis could be used https://en.wikipedia.org/wiki/Pyrolysis
The real important factor is that the hydrogen, either for fuel cells or for synthetic fuels, must be produced in a non carbon-emitting way. For example, the US Navy aircraft carriers can produce jet fuel from air and seawater using some process powered by the onboard nuclear reactors. Nuclear is carbon free energy so the resulting fuel is carbon neutral, it was made from carbon already existing in the atmosphere and will not change the total atmospheric carbon when combusted. This is why installing vast quantities of carbon-free electricity is important. Heck this can even be done on a local level https://archive.ph/HqJjU
Carbon capture is also a necessity but requires more electricity generation capacity. So of course, we must generate the electricity in a way that does not produce more carbon emissions. Most electricity comes from coal right now, which is why I advocate for electrification using non-emitting power generation like nuclear supplemented by solar and wind. There are a multitude of methods for carbon capture such as BECCS. https://en.wikipedia.org/wiki/Carbon_capture_and_storage
the big argument for synthetic fuels is that they don't depreciate existing capital. But if you make synthetic fuel out of plants you are competing against food production, and if you make it from hydrogen and captured carbon you have an extra energy conversion step with additional efficiency losses in your energy supply. You can make synthetic fuel in direct solar conversion which draws hydrogen and carbon from the air in a catalytic thermal reactor, or via algae, but also consider that fuel cells will likely be able to use both h2 and synthetic fuel. I think that H2 and Synfuel are close contenders with H2 having a slight edge, especially since there has been some progress in getting rid of rare metal electrodes, getting higher temperature resistant proton exchange membranes, and cheaper thinner insulation for cryogenic H2 storage.
So to summarize; the future of transport lies in synthgas and H2 cells alongside nuclear energy and solar/wind.
Public transport is probably going to supercede the need for in-city cars for the most part but people should be able to have cars and moreover Unless an established city is properly constructed it is not possible to effectively fully implement public transport as you could in cities planned for this problem. This applies to suburbia too; they're extensions of the city transitioning to the more rural areas. https://www.youtube.com/watch?v=JGVBv7svKLo&ab_channel=CityBeautiful https://www.youtube.com/watch?v=CWKuCoSg85w&ab_channel=EcoGecko https://archive.is/8qRJy