A Problem with an Overpopulation==Disaster Scenario
The following is a common illustration of why We Must Do Something About Imminent Overpopulation Immediately (quoted by Dan Gardner):
The problem with the above scenario isn't, contrary to Dan Gardner, that an environmentalist is more certain about the catastrophe than about potential solutions. It's quite common for some parts of a field of knowledge to be known to a greater degree of certainty than other parts. To put this is terms that my fellow wingnuts can understand, it's possible to be certain that funny money will lead to inflation and also disclaim the knowledge that can enable a government to pick winners.
Imagine a test tube filled with food. That's the Earth, he says. Now introduce a single bacterium to that test tube and let it grow exponentially. In the first minute, one bacterium becomes two bacteria. In the second minute, two become four. Four become eight. Eight become 16. If it takes one hour for the bacteria to multiply until they fill the entire test tube and there's no more food -- and the bacteria all die -- when will the test tube be exactly half full of food and half full of bacteria?
In the 59th minute. Which is strange because at that moment things look fine. But the very next minute, catastrophe strikes.
The problem with the scenario is that it points the reader's attention at the ratio between the time until Disaster Strikes and the total elapsed time (in this case 1/60). The important ratio is that between the time until Disaster Strikes and the reaction time of the organisms in question. That is likely to be less spectacular.
There's also the little problem that bacteria use up the nutrients but don't produce them. That's unlikely with humans.