A)photosynthesis
Nothing more to say
This doesn’t make sense lol
Well there are many catastrophic scenarios that we already overcome. You should consider educating yourself about the great filter. A great filter is a hypothetical barrier that each civilization can or cannot overcome. From here on things get a little complex so I won't bore you with them. But there are experts in this theory called great filter and I'm sure they can tell you a lot about.
Immigration and emigration is typically done with the purpose of looking forward to a better and more prosperous life, a more comfortable life where the money you earn can last you a pretty long time and buy you enough thing to live more comfortable than where you used to live. Therefore, when you move to a prosperous country, having children is not something you’ll worry about given to the commodities you’ll have and the easy access to baby food and baby clothes and stuff, therefore, when people emigrate/immigrate to more prosperous countries, they’re comfortable with the idea of having more children, and that leading to population growth.