Hurricane Katrina showed us how difficult it has become to distinguish between natural disasters and man-made ones. First, the Army Corp of Engineers decides it can build a better river than Mother Nature and in the process deprives the delta of storm-absorbing wetlands and barrier islands while allowing the ground under New Orleans to subside into a suicidal bowl. Then a storm hits and... well, you know the rest of the story. The lesson is simple: we are embedded in natural systems and whether we acknowledge that or not can be a matter of life and death.