In his bestselling book The World Without Us, Alan Weisman considered how the Earth could heal and even refill empty niches if relieved of humanity's constant pressures. Behind that groundbreaking thought experiment was his hope that we would be inspired to find a way to add humans back to this vision of a restored, healthy planet--only in harmony, not mortal combat, with the rest of nature. But with a million more of us every 4 1/2 days on a planet that's not getting any bigger, and with our exhaust overheating the atmosphere and altering the chemistry of the oceans, prospects for a sustainable human future seem ever more in doubt. For this long awaited follow-up book, Weisman traveled to more than 20 countries to ask what experts agreed were the probably the most important questions on Earth-and also the hardest: How many humans can the planet hold without capsizing? How robust must the Earth's ecosystem be to assure our continued existence? Can we know which other species are essential to our survival? And, how might we actually arrive at a stable, optimum population, and design an economy to allow genuine prosperity without endless growth? Weisman visits an extraordinary range of the world's cultures, religions, nationalities, tribes, and political systems to learn what in their beliefs, histories, liturgies, or current circumstances might suggest that sometimes it's in their own best interest to limit their growth. The result is a landmark work of reporting: devastating, urgent, and, ultimately, deeply hopeful. By vividly detailing the burgeoning effects of our cumulative presence, Countdown reveals what may be the fastest, most acceptable, practical, and affordable way of returning our planet and our presence on it to balance.