Suppose the Flying Spaghetti Monster were to look at Earth’s population issues and decide to act. Suppose His Noodliness decides that the simplest way is to obliterate the country with the highest population, China. Big hunk of rock. From orbit. Only way to be sure, right? So how big a rock does it need to be? And what would be the short term and longer-term side-effects? If these are too significant, His Noodliness may consider obliterating India instead - lower (just) population, but more isolated.
Considering China is the fourth largest country in the world in terms of area, and is 1.30x10^6 sq km larger than the continental United States, I’d say a meteor large enough to obliterate it would be large enough to obliterate the rest of humanity as well.
“Obliterating” China would likely cause horrible effects across the globe - nuclear winter, for one. Possibly, molten ejecta falling across half of the globe, for another. Oven-like heat across a large percentage of the globe, blast damage, large quantities of water vapor and dirt suddenly forced into the atmosphere. . . subsequent disease among the few survivors, starvation, violent struggles for food.
Truly ‘obliterating’ the country of China would result, very likely, in the extinction of the human race, and would significantly change the environmental conditions of the globe for thousands of years, if not permanently.
A smaller strike might result in the death of the equivalent of the population of China, without the outright destruction of a percentage of the planet equivalent to the size of China, and the human race MIGHT survive it, having been knocked back to a feudal society, or worse.
Oh, I always love it when threads come up on meteor impacts, it’s an excuse to show this web page: Impact Earth which will allow you to plug in values for yourself, and see the effects. Try some values for near Earth asteroids, they make the news once and a while, that you can get from wikipedia, and see what happens. Adjust size until you get the effect you want. It’s great fun … er, a good way to learn.
Rather than one big rock, a bunch of tiny ones would be better! A projectile with a 1000 ft diameter going 10000 miles a second should create a mushroom cloud that destroys or damages everything within 500 square miles.
IIRC the majority of China’s population lives near the coast. In that case drop a number of smaller meteors around the coastline and let tsunamis do the work.
You won’t get all of China this way but you’d put a serious dent in their population. I would think the global effects, while almost certainly still there, would not be too awful.
1.3 billion meteors, each the size of a baseball. With uncanny aim. Now that would get evangelists going!
That’s about 5% of the speed of light. Yes, that would do a lot of damage.
20 km/sec would be a more typical speed for an Earth-impacting asteroid.