That's not feasible. Even the most isolated nation-state in the world (i.e. N. Korea) has a hard time getting its high tech projects finished if all of the other countries are working against it. And they have the advantage of a fanatical following and oppressive control of the military and media.
Something on this scale would be pretty much impossible to pull off if all the G-8 countries put you/your company on an embargo list for high tech materials.
North Korea is making Nukes to threaten the world with. And is a tiny shithile country with an already destroyed economy.
It helps to be claiming to be acting in humanity's best interest instead of obviously being a despot. Think about the political aftermath of interfering with someone claiming that they are trying to save the world and having a reasonable argument that is the case.
Someone attempting this would likely be in a major country and would likely have the approval of most of the countries. If the USA attempted no amount of embargos could stop them, the same with Russia and maybe a few other countries.
It is even possible that Germany, France, Israel or South Africa could pull it off with a little politics and clandestine dealings. They could delay politically and pester larger nations and demand UN actions while continuing development.
If the US and Russia were dead set on stopping they could with a few bombing runs from aircraft carriers. I don't think that is likely because neither of these countries is crazy and would love to be saved at no cost while having a political bogeyman they can use in the future.
EDIT - Have an upvote for a thoughtful and reasonable reply though.
So, just to be clear, you want to impose your will on the planet, as a whole. You don't care about any form of democracy. You don't care what anyone else thinks. You think you're right, and anyone who opposes you is wrong. And since you're right, you're justified in doing whatever you think is necessary.
Vast tragedies throughout history were perpetrated by people who thought they knew better than everyone else, that their ends justified imposing their means on the rest of the human race.
Your attitude is dangerous, because you can use it to justify anything (e.g. you think you're about saving lives). It is evil, because it places you above everyone else and leads to death (e.g. you think you're saving civilization, which requires destroying the bad parts of it).
You either have not learned from history, or have learned the wrong lessons from it and are following in the footsteps of millennia of anti-heroes.
If I pull off some massive project like this what is another person/business/country going to do about?
If someone "solves" climate for some value of solved are you going to invade them and start a war over your economy being saved?