That goes without saying, but if the change is not just a slow and natural one, or develops unlike the normal slow and natural ones we all agree are happening all the time, the results could be more dramatic. Things change, but our tenure and effect on this planet is explosively fast compared to most climatological or geological processes. Even human processes in the past were glacially slow compared to the last two centuries or so, and they show no sign of stabilizing in the near future. Sooner or later our luck will run out, and I fear it will hapen before we even realize it.

The fear is not that the world might change, it's that it might change dramatically, in such a way that we can't adjust to it in time. I'm sure rain forests like the Amazon have disappeared in the past, due to natural causes, or icecaps have melted, or coastlines have been inundated. But I doubt many of these things happened in a generation, and certainly not to a society whose industry and agriculture and economy required some measure of stability.

Even purely natural changes may challenge our ability to adjust. If these changes are aggravated by our own activities, the results could overwhelm us. It may not be a planet-crushing catastrophe, but just consider what might happen if the monsoon stopped, or the western plains became a desert, or Europe acquired the climate of Labrador...all in just a few decades.