According to my curve fits, the world ecological footprint per capita for sustainability would be what it was in 1951 (about one acre per person); and we would have to reach that point between 2013 and 2017 to avoid casualties from over-consumption. Any improvements to the equivalent lifestyle would need to be zero-waste.
If we start reducing our footprint at the end of 2006, the annual rate of decrease in the footprint will need to be 14 percent; if we wait until the end of 2007, the required rate will be 17 percent; and if we wait until the end of 2008, the rate will be 21 percent. If we wait until the end of 2012, we will be unable to avoid casualties.
I did realize that what I was calling zero population was actually about what the population was projected to be in 1915, about one billion people. Although what happens when the population takes a nosedive can accurately be described as a crash, I can’t legitimately say that the population will drop to zero (though it could).