eventually, we're going to run out of nearly everything.  especially land.  unlike, say, oil, there is no hope for discovering any vast, unknown reseviors of land.  we're pretty sure we know where is all is (opinions vary regarding atlantis and mu) and it's not like new land just springs up out of the depths of the sea (okay, well, it is rather like that, but too slowly to be of much use.  not to mention unstable).  as a general rule, if lost continents suddenly reappear, they tend to bear cthulu or some other unspeakable horror or blasphemy from beyond the stars anyway.  so, best to stick with what we've got.

land is the limiting factor.  it can only bear so much, and there is only so much left that is a) arable and b) not already being used anyway.  people aren't going to give reproduction up anytime soon.  mandatory sterilizations, birth limits, forced abortions and contraceptives all carry a heavy price in human rights violations, to start.  so, how do we continue to feed ourselves?

some people think the inevitable result is human migration to the stars; starting with moon and mars colonies.  these people tend to be a bit too into science fiction.  besides, you cannot farm the moon or mars (and theortical terraforming of mars would take an awful long time).  besides, a pre-requisite to such a migration would be, perhaps, a viable solution on earth.  that is, advances in hydroponic farming.  utilize the same solution cities have been implementing for years: when you can't build out, build up.  sure, i have no idea how to manage it, but it seems the logical course of action.  we already know how to grow some things via hydroponics.  we're going to eventually run out of land.  why not hydroponic skyscrapers? 

yes, because water is a finite resource as well.  granted, it is also reusable (provided we clean it well enough).  there is desalination and iceberg harvesting, but those will only go so far.  ice cap and glacial melting limits iceberg harvesting.

global warming skeptics are an interesting lot.  there are those who flat out deny the globe is warming (silly, because it's measurable) because, oh, it still snows in january or because there was a hotter july 120 years ago.  these people tend to just not understand averages, the difference between global and local, or the difference between climate and weather.  there are those who refuse to see any human hand in climate change.  they point out truths such as the fact that the earth's climate has varied over its 4 billion year history.  well, sure, so?  or that methane and water vapor are more effective greenhouse gases.  again, true, but so what?  methane is a non-factor in the atmosphere and atmospheric water vapor is limited by temperature.  once the atmosphere gets oversaturated with water vapor, it, uh, rains.  it can, however, inhance warming since warmer air holds more water vapor.  and so on.  one of the arguments against any mitigation of co2 emissions is the "who are we to say what temperature the earth should be" line.  well, here's the thing most people forget.  preserving the environment is important for human survial.  why is extiction a problem?  because high biodiversity is good for all creatures: more for us to eat.  pollution?  kills us, that's bad.  kills our food, also bad.  a warming climate?  again, it is potenitally harmful for humans directly, and through our food supply.  the planet doesn't care what temperature it is; humans do.  sure, life will go on regardless.  it's rather difficult to completely irradicate.  even if we were somehow able to wipe out all life (including bacteria) on the land, we've still got entire chemosynthesis based ecosystems that will likely continue.  but, our species may not make it, and that's a problem for those of us who enjoy existing.  self preservation, pure and simple.  regardless of any noble and altruistic import we may want to tack on. 

i liken the the skeptics to alcoholics who figure, well, i've got cirrosis already, why give up drinking?

there is no money in thinking long term.  at least not any short term profit.  this is why we're seeing car companies battle the rising costs of fuel by offering fixed fuel price deals, instead of working feverishly to improve engine efficiency and thus gas mileage or offering feasible alternative fueled vehicles.  think about it.  our energy infrastructure is still, basically, based on late 19th, early 20th century technology.  sure, it's been tweaked, but the underlying priciples haven't changed in nearly a century. 

hell, we may be in the midst of a magnetic field reversal right now.  the magnetic field has been slowly weakening for years.  of course, this also leads some lunatics to claim it means the core is going to stop spinning and we'll lose the magentic field and die!!!!!  instead of the far more likely (and historically, okay, prehistorically, overdue) field reversal.  i kind of think it might be fun and am wondering if it will seriously fuck with birds.

anyway, yeah, sure.  the earth goes on about its business without worrying much over the bugs on the surface.  hell, increased warming may actually make it colder by shutting off thermohaline convection, though opinions vary as to just how important that is to moderating northern marine climate.  given the sheer number of variables that go into determining climate: albedo, milankovic cycles, position of the continents, plant life, animal life, bovine flatulence, topography, bathology, etc.. one can certainly say "fuck it".  it's going to do what it will.  and yes, sure, it will.  doesn't mean we should hurry it along though.

ah, long term planning for shortages though.  here's why it doesn't happen.  say there is absolutely convincing evidence that fresh water would run out in 20 years if action wasn't taken to conserve, clean and resuse water.  action is actually taken (for once).  water rationing is imposed.  a special tax is levied to pay the billions that go into overhauling the sewage treatment infrastructure of the nation, develop effecient desalination plants and pay for research into new well drilling methods and more efficient irrigation.  everyone has to buy new toliets, shower heads and faucets.  prize-winning suburban lawns wither.  colonge and perfume sales skyrocket.  bakyard pools are filled in.  goldfish go free.  people stop building golf courses in the middle of deserts.  there is a palpable pinch felt by all.  twenty years pass. and then a gaggle of scientific heads hold a press conference saying that new analysis indicates water supplies should last for at least 200 more years...before they can mention that means "at current usage rates" and "thanks to the conservation efforts put in place" the nation collectively cries "what the fuck!?!?!?  you bastards said we were going to run out and so i gave up golfing in death valley and now we've got tons of fucking water? what the fuck?" and the scientists are summarily lynched.

maybe that's when alien conservationists come to cull the herd? 

"you bastards said we were going to run out and so i gave up golfing in death valley and now we've got tons of fucking water? what the fuck?" and the scientists are summarily lynched."

Maybe not summarily lynched. Give them a chance to explain why the erred on the side of caution, and then lynch them. Fucking scientists. Next thing you know, they'll be trying to figure out a way to actually extend our stay here rather than simply trying to figure out how to stop the train.