Re:End of the world
The problem with precipation patterns is that adaption is dependent upon local geography and resources. One perception I developed a few years back was the possibility of detrimental changes of rainfall hitting the Great Plains of the USA.
Granted, it's a huge geography, but I'm talking long-term. There are already drought issues in certain areas, and with the US agricultural sector already heavily subsidised the possibility of it becoming increasingly vulnerable would set a very regretable set of circumstances.
Of course, rainfall isn't the only issue - worse and more frequent east coast hurricanes, stronger and more frequent mid-state tornadoes. Then there are the temperature differences and how that affects soil fertility, not to mention the spread of tropical disease into temperate zones - not simply dramatic human disease, but dramatic plant disease and even those that would attack cattle etc.
Sounds a little alarmist, but over the coming decades the US agricultual sector (not to mention others) is going to face serious issues related to Global Warming - a very issue it practically denies even exists.
As for China, though - it wants to play the power game, sure. But they're playing a global game. It's not a case of military domination, as much as economic, that they appear to want to play at. And doing so would certainly be a challenge to any agressive ideaology.