Homer-Dixon sent out a recent email on updated activities, and a visit to his site led me to read above-linked article on complexity. Complexity is one of the most interesting, and I think productive, theories to arise on my intellectual horizon. It applies to natural sciences and social sciences (which, of course, shade into one anther). Homer-Dixon gives a succinct description of complexity theory and of "panarchy", taken from the work of his fellow Canadian, "Buzz" Holling.
This article deals with climate change, Homer-Dixon's current number one concern. Unlike the enigmatic Seth Roberts (a UC Berkley/Quinghua) professor who takes appropriate skepticism to an extreme of denial, Homer-Dixon looks beyond theoretical skepticism to realities, such as the Arctic, and says we'd better sit up and pay attention. I really admire his work. Deep theoretical understanding combined with first-hand observations and engagement make his work the most compelling and important that I've read on the issue (burning, literally) of climate change.