What unprecedented measures could be taken to stop climate change?

I think some kinds of global carbon tax + other green house gasses (GHG) done at a WTO type level.

Stop telling people what they can/cant do this and focus on pricing the damage points. Puts costs against goods like meat production, petrol cars, private jets etc. Rather than moralise, put a price on them and give people the choice. This will encourage farms to use seaweed to reduce cattle methane or bring in electric planes or goods that last longer.

Ideally this could be taxed at a national level. And for countries that wont, put export/import tariffs on them from the trading block to meet the cost they should have taxed. Monies raised must go towards environmental improvement measures e.g. buying land for forest regrowth or carbon scrubbing.

Obviously huge global plan with masses of detail and nothing is perfect, but generally I feel putting agreed globally consistent costs on GHG emission seems the best way to redirect the world to better behaviours.

Nuclear https://youtu.be/N-yALPEpV4w

Simple but not easy. Difficult to enforce however.

Here goes:

Non-recyclable packaging for food items is illegal as a first step. Other packaging is staged for later. No more than 10 years to implement. No excuses for anything that goes into a home to have non-recyclable packaging after that 10 year changeover.

Fossil fuels can't be sold anymore. Fossils can be used for various long lasting purposes. Not for disposable purposes, eg face masks.

Computers and similar obsolescence landfill items (IoT) must be completely repairable/upgradeable and/or at least realistically reclaimable. No excuses. Companies failing to do this are billed for the existence of the item and must track it like nuclear waste. Think in terms of landfill storage fees.

That's just a start. Good luck.

Buy coal mines, coal generators, and petroleum refineries in developed countries, sit on the coal and dismantle the generators and refineries to destroy fossil fuel supply and force consumers to cleaner options. China is harder considering the authoritarian regime, but conversely they are deploying renewables very quickly because they don’t have nimby or property rights barriers (and they have a voracious demand for energy).

You want to find ways to dismantle fossil infrastructure in a manner that is too burdensome to go back once you’ve taken action. The only way forward is then lower carbon technologies (and yes, natural gas use may temporarily increase, but that will incentivize faster deployment of cheaper renewables paired with energy storage).

My company takes part in https://stripe.com/climate That's where soon billions USD can be spent (some projects are still in research stage).

"Stripe is kick-starting market for carbon removal" https://news.ycombinator.com/item?id=29007726

Consensus and urgency among a vast majority of world governments.

Just OPEC may be enough, but there are a lot of non-OPEC controlled oil reserves, and OPEC controls haven't always been super effective. If OPEC announced (and held to) a coordinated reduction in production of say 5% a year, I don't know if other sources (or OPEC defectors) would make up the shortfall. A strong signal of reduced availability/increased prices of oil would increase motivation to use alternate energy sources, some of which have reduced emissions.

Moratorium on human procreation until we have a sustainable transition off of fossil fuels. Really it's just cruel at this point to continue to play this game where more people are brought into being, presumably for their parent's personal happiness, but have their futures shortchanged by the previous generations' lack of action.

Dump a couple container ships of powdered iron oxide in the oceans. I would not recommend this, as it could lead to global agriculture collapse and mass starvation due to lack of crucial component for plant growth. Plants require carbon dioxide...

The book "Super Freakonomics: Global Cooling, Patriotic Prostitutes, and Why Suicide Bombers Should Buy Life Insurance" discussed one method that only costs on the order of millions of dollars a year -- I believe it was putting sulphur into the atmosphere to cause a cooling effect. It certainly sounded worth considering.

Billions in funding for modern fission nuclear reactors in the short term. Trillions in funding for Fusion power plants for the medium term.

One unprecedented step in this direction would be to shift fossil fuel subsidies into nuclear subsidies. You probably want to do that part in stages.

Pretty much any measure taken to stop climate change would be unprecedented.