Lots of interesting posts here.
My understanding of the 911 business is – current consensus – that contrails and often-ensuing stratus (same with ship exhaust) do more to prevent heat radiating outwards than they shade the Earth's surface.
Yes, let's face it: overpopulation is the Big Daddy of our problems every which way. We're choking the whole works. But lay off Africa, hitherto relatively lightly populated. India yes, scary, and when combined with China will, in a few years, amount to Three Billion people, far higher than total world population the day I was born – and I'm 64. Those two Industrial Giants ain't stoppin' for nuthin'.
So, after staying just one jump ahead of our own extinction for hundreds of thousands of years, we now have runaway overpopulation which spells ... our extinction. Along with that of millions of other species.