Russia will have unexpected gains in Ukraine and US will decide to directly intervene using armies from Poland, Baltic states, Romania, Slovakia, Czechia, starting the WW3, escalating beyond all prior limits rapidly. EU will get completely nuked within a day, destroying all cities above 100k, leaving only pockets of rural areas survivable. UK and Ireland will be swept by a massive tsunami from a nuke detonated underwater. There will be a full-blown nuclear exchange between the US and Russia, wiping out most countries in the northern hemisphere in the process, reducing human population to 1/10th of the current level within a year, leaving only parts of South America intact. Humanity will enter another stone age with no chance of rebuilding the civilization due to having all surface-level resources exhausted and will turn to cannibalism to survive, however Earth will be too damaged to carry life and will slowly become another Mars with deadly background radiation everywhere. Metro 2033 will be renamed to Metro 2023.
It's just a prediction on the very negative end of the spectrum. It's done in military gaming all the time ("what's the worst that could happen?") but typically nobody treats it too seriously exactly for the reason you mentioned.
> There will be a full-blown nuclear exchange between the US and Russia, wiping out most countries in the northern hemisphere in the process, reducing human population to 1/10th of the current level within a year, leaving only parts of South America intact
I just wanted to give a nod to all the other countries in the southern hemisphere, since some also have a likelihood to miss out on a nuclear Armageddon: Australia, lower Africa, Madagascar, New Zealand, potentially some of the South East Asian nations, and a whole bunch of island nations, Antarctica.
I would be surprised if NZ didn't have any nukes pointed at it due to being the favorite spot of the western elite for survival arrangements. For Australia only a few coastal cities need to be taken out as well. I think some parts of Argentina, Chile, Brazil and maybe Uruguay stand a chance of being untouched, maybe South Africa as well.
It's my opinion that in a nuclear Armageddon, it wouldn't just be a free-for-all for every nuke to be let fly at every country currently at odds with each other. For example, if Russia and US trade nukes, I wouldn't expect all other WMD wielding country to just start attacking every country they're in poor standing with.
For Australia in particular, we don't have nukes so we shouldn't be on anyone's Mutually Assured Destruction ledger, and if not that then it would be an opportunistic nuke, the purpose of which I can't fathom. It would be better to take Australia by conventional means and keep the infrastructure in tact, since without our allies we have very little defense.
It was revealed that during Cold War there was a plan to nuke all cities over 100k inhabitants anywhere in the world so that no civilization can restart anywhere. For example, some nukes on Ukraine were pointed to China, a somewhat ally of the USSR at that time. I don't think Australia can rely on being non-nuclear to escape if SHTF.
In your scenario I would predict that 70-80% of russian nukes and missiles malfunction due to poor maintenance / disobedience / sabotage / some existing only on paper / pre-emptive strikes due to intelligence of imminent attack.
Most of the rest end up being destroyed by already established anti-missile defenses.
Starlink ends up being a missile defense in disguise and Musk ends up being hailed as savior of some US cities after sattelites do kinetic intercepts of a lot of missiles entering space. (even though it would probably be a us dod takeover of the the sattelites)
Putin and company gets gaddafi treatment.
Russia promptly unconditionally surrenders after NATO campaign and nuclear retaliation threats
or actual detonations based on how many they got through.
