or the potential risks that history has yet to throw at us at all.
I'm fundamentally optimistic about the future.
I think the odds of another major terror attack (and subsequent revenge invasion) are significantly greater than zero, and I have a short list of personal favorites that I can't believe no one has tried yet. Flying airplanes into buildings was a good one, but there are a bunch more ways that bad people could do major harm with limited resources. I think most people don't realize how fragile civilization really is.
I wouldn't be surprised by a devastating outbreak of some antibiotic-resistant pathogen taking 10% of the world population in my lifetime. Such diseases already exist, and new ones are evolving faster than our drugs are. I don't think anyone believes our ability to scale up the production of new antibiotics can possible compete with exponentially growing infection numbers, so this is one of those deals where we rapidly lose control of if we don't stop it up front. The planet has never had this many people living in such close quarters before, we're ripe for infection.
Natural disasters happen with some regularity. What would the US economy do if Mt. Rainier wiped out half of Seattle? If the Hayward fault took down half of Northern California? Katrina was a speedbump in a second-tier city.
War. Always war. It's what humans do. There are lots of ways for this to unfold next time, but my money is on some combination of the Middle East and China.
Climate Change. In most places, changes will be slow and gradual and we'd have no problems adapting. In some places, those slow changes will lead to very rapid shifts. Plate tectonics was slow, too, until South America suddenly disconnected from Antarctica and connected the Pacific and Atlantic oceans for the first time in a billion years and dramatically changed the planet's ocean circulation pattern. That's the sort of problem with climate change I'm worried about.
Generic population growth. There are currently more people living in southeast Asia than in the rest of the world combined. I don't claim to understand what impact that will have on the future of the planet, but I don't believe it will be irrelevant to the next century.
And despite all of that, I still think the future of the world economy looks better than the past. Standards of living are rising. The rule of law is expanding. Life expectancy and literacy rates are climbing. We've already survived a bunch of that bad stuff listed above, and we'll get through some more of it, but I still think the general trend for humanity (and the stock market) is up up and away for the remainder of my own short life.