"A question in the air: Are you an optimist or a pessimist? You have to figure out how to feed 7 billion people reliably (a billion right now are going hungry or have inadequate nutrition; 3 billion live in poverty on less than 2 dollars a day), and give them clean drinking water, and sanitation, and then factor in population growth of an unknown degree (will we hit 9 billion? 10? 16?), and then factor in people living much longer lives beyond their prime productivity years (by mid-century the median age globally will have gone from 29 to 39), and you have to do all this on a planet that is heating dramatically, with acidifying oceans and dwindling forests (losing a Switzerland of old-growth annually, we're told) and precious resources getting scarce."