I just read a great (but too scientific to post for most people – ask me for citation) on some rainfall research.
It was great because in the heated debate of climate change, it was remarkably neutral and objective and practical. Their research shows that the rise in carbon started between 300 and 1000 years ago. So it was way before humans started emitting carbon. But it has sped up recently, so we are probably making it worse.
The result that they are worried about (and the subject of their research) is that the band of good rainfall is moving north. By the year 2100, the land between the equator and Arizona/Florida/Italy/S. China/etc. will not be suitable for farming.
So we have two choices. We can keep arguing about who is to blame and have to deal with the results rapidly and painfully in 50 years or we can agree that it is both natural and human-caused, start now, do it gradually, and hopefully without much pain.
My favorite option is the urban model. The idea is to create high rises that have shopping on the bottom, then offices above, then housing above that, and then hydroponic farming units at the top. Each building could be totally self-sustaining when necessary, but for variety’s sake they can all be different (different shops, different companies, different food growing, different types of condos). And they can be done in low rainfall areas.
The other option is to start moving farms from currently fertile areas in the soon to be dry zone northwards. We have lots of available land in Alaska that will become very fertile when the band gets there (again, by 2100).
Both of these would be rough to shift to in 10 years, but we have 80-90 or so if we start now.