How much warming have we had so far? How might this affect the weather?

The one major flaw in your thinking is that 1 degree change is everywhere, i.e. 1 degree in Texas, 1 degree in China and 1 degree in Antarctica, etc. The fact is that the 1 degree change is a GLOBAL average. This means that some areas of the globe are heating quite a bit more than 1 degree and some other places might actually be cooling a bit. The poles have warmed an average of 10 degrees while the American desert southwest has actually cooled slightly due to increased precipitation. It is this wide range of change that is capable of changing large atmospheric or oceanic circulations and bring about mive climate change. I'd suggest reading something better than your "Idiot's guide to..." book if it didn't even outline this very basic premise of the climate change argument.