Well we could do as we have done from the beginning , let the poor in famine stricken regions die off.
Implement something like Larry Niven's birth right policy, basically put down the number of kids you have to a lottery unless both parents are of exceptional intelligence.
Go to the level of say Make Room Make Room, Harry Harrison's concept that in the end comes out as Soylent Green is people.
Get of this freaking planet.
Or as in Logan's Run, everybody over 30 is killed.
For the most part people in the future will die.
I'm with Larry Niven on this one birth right lottery. Every one can have one kid, you have to win the lottery to have two and win it again to have the third .The problem on the intelligence side is how do we determine who is intelligent and that a twit who has a few billion dollars does not get to have more kids than they should.
For that last one look up the Marching Morons by Cyril Cornbluth.
If can think of it now, realize that someone thought of it 50 years ago.
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We are currently adding 100 million people a year to the global population. It's utterly impossible to export that number of people off the planet. If we continue at that rate, in 200 years the population would be around 26 billion, not 10-12 billion. Clearly we can't continue as we are--the global fisheries have essentially collapsed during my 60 year lifetime--and clearly we can't export billions of people off the planet when we can't even afford exploration missions to Mars, so population control is the only realistic answer, especially if average life spans increase. That means that certain human populations will have to quit breeding like rabbits, and soon.
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It's not popular as an opinion but I think we will need to institute a "Stop at Two" form of population control eventually, with occasional relaxations if populations begin to decline.