That's 4 billion nearly starving people eating nothing but tofu and bread. Meat would become such a luxury product because the only way to feed the cows would be to farm them exclusively on grass, which is less common than you think. That leaves 4 billion people who have literally nothing.
The greatest impact would be china, India, and Africa. These three regions alone have half the worlds population.
Ironically one of the only first world countries that wouldn't face starvation directly would be the United States of God Bless America. And this would make us the target of the inevitable resource wars. When every starving faggot on earth decides to pile on us at the same time, desperate for whatever we can give them. Faggot Liberals would demand we let in the refugees despite the fact that this would literally be the same as trying to rescue a drowning man by swimming out to him. They would eat what little we have and then we would all starve. Russia has a population that they can't sustain with their farm land, despite their size tiny Ukraine has more cropland. Russia would not be pussyfooting around like they are in Ukraine right now, they would begin glassing cities to take what they need. In fact if I was a betting man this the real reason the war in Ukraine actually started; Russia might be running out of oil, and know that everyone else is too. They might also fear a global supply chain shutdown, believe it or not they also need that shit. If they could take Ukraine no amount of dead ruskies would outweigh the chance of having one of the few places on earth where you could reliably grow all the food you would need for a country the size of Russia.
you think it's a refugee crisis now? with a few tens of thousands of darkies crossing into Europe? Africa would begin marching north like rats abandoning a ship, they would not stop until they got to Europe and took everything.