 We've seen 100-foot-high waves in the oceans in huge hurricane-force storms. But, yeah, if you crank up the wind speed, I don't see any reason to have even bigger waves than that. The idea of black swans, where things that were thought to be impossible turn out to really exist, has become fairly popular now. But the American scientist Kerry Emanuel is worried about gray swans. Can you tell us about that, Jeff Masters? A black swan is an event that's totally unexpected.