As we learn more about the ramifications of climate change I think it would be irrational not to worry. I live in a civilized country with modern building standards and easy access to food and clean water so I'm not too concerned about myself. I'm very concerned about the many millions of people who don't have that luxury. If you're already on the razor's edge increased flooding or increased drought could be the difference between life and death. We also have to consider the political ramifications of mass migrations due to people fleeing floods, mudslides, drought, changing animal/insect populations and their impact on agriculture, etc. I think you're right that it's not really anything new, weather patterns have always been subject to change, but we have more humans on the planet contending for ever more scarce resources today.