The short answer is: that's a complicated question. There are reasons to be worried and reasons not to be, but neither have to do with what you mentioned.
Don't worry too much about food. There is more than enough to go around. The only reason why there is starvation is because of the logistics of getting...
Best answer: The short answer is: that's a complicated question. There are reasons to be worried and reasons not to be, but neither have to do with what you mentioned.
Don't worry too much about food. There is more than enough to go around. The only reason why there is starvation is because of the logistics of getting it to everyone (some people not being able to afford food, there's only so much food we can ship to underdeveloped countries, etc.). Moreover, making more food is not an impossibility, even using the same amount of space. Cows, for instance, are very wasteful when it comes to space, as they eat a lot of grain, which takes up space to grow, in order to produce not a ton of meat. As the population grows, we will probably see the price of beef, dairy, and other space-hungry foods rise and demand will increase for other, less space-hungry foods. In turn, people will grow more of those foods and the problem will fix itself before it ever becomes a matter of starvation. We're actually seeing that happen already as many dairy farms are shutting down.
Mars is not our savior. If we will ever be able to sustainably on Mars, it will not be for at least a generation. That takes a ton of planning, and even if everything goes smoothly, we won't have a village-sized colony there for many decades. Everything will have to be imported. Think of all the things that are necessary for life- oxygen, food, water, thermostasis, shelter from the dust storms- all that has to be accounted for.
Water is a much bigger issue than food, but poor places will be hit first and hardest. If you live in a first-world country, you probably won't see anything worse than a bit of rationing in your lifetime. That might look like only getting to shower every other day and not being allowed a lawn because they're an unnecessary use of water. Poor places might suffer from mass dehydration.
Poor places, currently, are the ones over-breeding, while many developed countries are in fact not reproducing at replacement level. It's a horrible "solution," but as more of the places we accept immigration from to make up the difference become unlivable, their death rate may come to match their birth rate, thus causing population growth to slow.
Ultimately, it won't come down to whether the population gets larger (it likely will) but whether developed countries do what is necessary to support a larger global population. There are so many "ifs" when it comes to this, but humanity has worked past so many crises before that it seems unlikely that this one will do us in.
4 weeks ago