I'd never have thought that either - being influenced by the...

I'd never have thought that either - being influenced by the media that CO2 levels rising is a BAD THING. But then I asked a Q on hc, why is warming a bad thing anyway? So I did a search, and found that link. That shows deaths from extreme weather events have declined 98.5%. So if the earth is truly warming, whether CO2 caused or not, it must, in one respect, be a good thing. And if CO2 causes more warming, on the evidence collated in that link, that should continue the trend, and be more of a good thing.

Why would anyone assume a change is for the worse?

The worst floods in white man's knowledge in Brisbane were probably in 1893, when the levels were double what they were in 2011. Previous to 2011, the worst were: 1974 (37 years ago), 1950 (24 years earlier), 1931 (19 years earlier): notice a local trend too?