the thread seems to have derailed slightly. It's original purpose was
to discuss a short term possible extinction event
An extintion event caused by lack of food, excess pollution, and too many people. The segue is that, "too many people" doesn't need to be an extintion event because the earth can accommodate a lot more people than the people in your study realized. Largely because apparently people have a "gather stuff and then it's gone" mindset, and the universe doesn't really work that way.
for maximum efficiency food-wise, we need to become vegans.
There's no need to grow animals in order to have meat.
http://en.wikipedia.org/wiki/In_vitro_meat
There's a problem you can't circumvene though. Population pressure will eventually break down human society. Humans(like any species) can't survive with a constant high population density
...already addressed multiple times: we're building in three dimensions.
The most important problem will be the weather though. Cities tend to absorb heat
That's not a problem. That's
beneficial, because the waste heat would be reclaimed.
This is, incidentally, a significant part of the solution for the energy consumption issue. One doesn't actually need to collect all those exojoules every year, any more than one needs to "acquire new dirt" to plant new seeds each season.
If you are talking about a population of trillions of people then you are not talking about "anytime soon". Many centuries if not a few millennia would be the better estimate.
...I admit that does skew the naure of the debate somewhat. If 6.3 trillion people materialized overnight, that would be very different than if it were gradual growth over a few hundred years. And looking at even the fastest predicted
growth rates, we would have those centuries.
Honestly I think a few decades would be enough time to finish up all
technological requirements of supprting trillions of people. We're almost there. The majority of everything discussed so far could be done with today's technology. But the
infrastructure would take quite a lot longer. And if we do have centuries to work with...I think that the technological advances in that time will make a lot of our accounting now pretty much irrlevant. I've been avoiding futuristic Star Trek style solutions here, but we've gone from our very
first flight to
sending an object outside the solar system in roughly 100 years. So...looking to what we'll be capable of 100 from now...stuff like interplantary teleportation and matter replication seems pretty reasonable to me.
In any case, the planet herself would have no problem accomodating trillions of humans. It might not might not actually happen...but the people saying it's "not possible" aren't any different from those who thought it impossible to fly, to travel in space, etc. Of course it's possible. In fact, even saying it now...I suspect that "trillions" is probably a pessimistic figure by several orders of magnitude. If we simply colonized down like ants, the available space is so large that I don't have an intuitive grasp of it. And each level we build up has more surface area that the last. Space is totally not an issue. It's just a matter of providing proper input and output in the form of food, water, climate, plumbing, entertainment, communication, etc. And those are all simply engineering problems.
Trillions is no problem. It just a question of what technology is required to fill in the empty gaps in what we can do.