JARED DIAMOND: Is the world facing any crisis? Yes, you will not be surprised to learn from me something that you already know, that the world is facing various crises, of which I would pick out four as being the most serious crises. The crisis with the most explosive potential for damage is of course, nuclear weapons. The risk of the U.S. and Russia getting into a nuclear war has now decreased. But the risk of India and Pakistan has increased. The risks of North Korea and the United States has increased.

And then the risk that terrorists either will steal a nuclear weapon, as they tried to do at the time of the World Trade attack, or that they will take a perfectly normal dynamite bomb, which they've been very good at blowing off in the central of Paris and Lisbon and other places, and just add to the dynamite bomb a radioactive isotope like cesium 137, which you can get from any hospital medical facility. You put your isotope in your dynamite bomb and blow off your dynamite bomb in the center of Washington, D.C. And then you sterilize for the next 132 years that area of Washington, which become radioactive.

Big consequences, so risk for the world is nuclear risk. Another risk of the world is obviously climate change, which has the potential for cooking all of us, cooking and drying out and raising sea level for all of us. The third risk for the world is running out of resources. The world is operating unsustainably now. At the rate we are going, we will run out of essential resources, fisheries, forestry, water, topsoil within about the next 30 years or so. Either we solve it in the next 30 years or we'll never get to solve it. And then there's finally the world risk of inequality. There's inequality not only between Downtown LA and Beverly Hills, there's inequality between countries of the world.

But poorer countries nowadays have-- in this globalized world-- have ways of visiting their dissatisfaction on rich countries by supporting terrorists or by forming unstoppable waves of immigration or unintentionally by poor public health systems, underfunded public health systems, which means that they can't cure their own diseases of malaria and dengue. But nowadays, in these days of international travel, American tourists go into other countries and visitors from other countries come to the United States, meaning that malaria and chikungunya fever and dengue are showing up in developed countries.

So those are what I see as the four biggest problems facing the world. I'm cautiously optimistic. By cautiously optimistic I mean that we have problems and we're capable of solving the problems because the problems that we face are problems that we humans are causing, such as climate change. They're not an asteroid racing towards us and there's nothing we can do about it. And how optimistic am I? It depends upon the choices that we make. I can't predict what choices we'll make. But I would say that I see the chances as at least 51% that my sons will end up in a happy world 30 years from now.

And the chances are no worse than 49% that they'll end up in a miserable world not worth living it. But it depends upon our choices. And I cannot predict our choices. If we make the right choices, we are guaranteed to end up in a happy world.