Well, we could just not maintain military bases all over the goddamn planet, and retain a mostly defensive military. More realistically, I suspect that significantly reducing overseas deployments would also significantly reduce the military's carbon footprint.
I do concede that this may not be geopolitically realistic. I also agree that nuclear seems like a realistic solution for carriers and combat ships. Just eliminating diesel-powered aircraft carriers would probably go a long way, I would guess.
But at the same time, let's not kid ourselves - this will result in more wars, except it wont be U.S. ships and planes burning the fossil fuels, the fossil fuels will be expended by foreign troops and all the rebuilding necessary as a result of more conflict.
Here is an article in the WSJ about the significant increase in coups in Africa as a result of the U.S. pulling back and Europe also easing off of its policing role due to covid:
https://www.wsj.com/articles/military-coups-in-africa-at-hig...
More likely, if the world was run on Uranium and Thorium then people wouldn't be able to blame wars on oil.
It's a valid point about the military, but all militaries run on fossil fuels and a handful of big carriers/subs that runs on nuclear.
During WW2, we ran petrol/oil pipelines from the UK under water to Normandy. Each pipeline was a steel cable rolled up along an enormous floating drum called a conundrum that weighed as much as a destroyer. There were 7 of them.
https://en.wikipedia.org/wiki/Operation_Pluto
Then we extended those pipelines on land as we pushed East. There were 73 allied divisions, each requiring an average of 7 tons of supply each day, with 2/3 of that being fuel. The USSR had something like 600 divisions.
Modern armies need even more oil as jets are thirsty. Oil and gas infrastructure is critical to modern warfare at the moment, and I don't really see electric tanks or jets on the horizon. So that's not going to be an area where will be reducing much CO2 any time soon.
Long term, perhaps hydrogen might be a replacement for vehicles, and smaller nuclear reactors even for combat ships?? But we'd need to be able to make a lot of hydrogen very quickly, and have something like a strategic hydrogen reserve for wartime. The explosive nature of hydrogen is also a challenge when you are being bombed and shot at, and there are supply chain issues as to what operation Pluto would look like if it was hydrogen.