Birth rate drops as survival rate improves. Good health care improves survival rate. If you want to go negative, economics, keeping people poor, also has an effect on reducing birth rate. I remember the days of upwards on 11 children in irish families. I was one of 5. Now the average would be 3. (Incidentally this is also mirrored in the rest of the animal kingdom; less predators, less offspring)

I believe that climate change and the shortage of water is going to happen much more quickly than most folks think. As ocean levels raise there will be a lot of people having to move inland and as aquifers dry up a lot of people will be short of water. What's left will be very overpopulated leaving less land for agriculture. Things seem to take a long time to happen but when they happen it occurs very quickly.

We as a species have broken with nature. We grow to much food, and medicine perhaps cures to many ills. Mother nature will win in the end. America may not be the bread basket of the world much longer. We are running out of water in the west. We have the ability to use birth control on a world wide basis, but I doubt we can organize well enough to implement an effect program. Good luck humans.

Global sterilization.

It seems to be a part of the nature of man to destroy our environment. Virtually ever4y ancient city that was abandoned was due at least in part, if not in totality to damage they did to their local ecologies. Now it appears we are doing it on a world wide level. Not having anywhere left to go, at some point the population will decrease due to our destroying and/or changing local econlogies, which will inevitably result in famines.

That's the intuition, right? More people being healthy meaning more people live. But that intuition is wrong. The better the medical conditions of a society the lower the birth rates become. Turns there is a worldwide trend of lower and lower birth rates even in 3rd world countries due to better medical care.
I guess women also don't feel forced to become mothers if they have better access to education and a career so that's also one good thing to do.
But laws to protect the environment, CO2 taxes and other incentives to reduce our reliance on limited resources is needed on a wider level. The USA being the biggest consumer needs to make the biggest changes. Let's see if we survive this century, good luck y'all.