Excellent article from Ryan Meyer of the Center for Science, Policy and Outcomes at the University of Arizona on the inadequacies of models that purport to assess the damages of global warming. Read the whole thing, but two specific points are well worth excerpting:
The a priori assumption that global climate change is the only global change problem we need to deal with is misguided. Starting with climate change as the central problem, and then building a model around variables that plausibly can be linked to climate change, will of course yield a picture of the future in which climate change is the dominant problem. If one insists on framing problems in global terms, climate should be just one of many changes important to the future of humans on Earth. The broad perspective of global change may provide a far more useful (and balanced) context for specific global problems like climate change.
A bottom-up approach to identifying and quantifying potential climate impacts is crucial to understanding the importance of climate change in socio-ecological systems. The marginal social cost of one ton of carbon emitted into the atmosphere – a number actively debated among environmental economists (e.g. Richard 1999, Clarkson and Deyes 2002, Pearce 2003, Guo et al. 2006) — is no more useful to the rural farmer in Zimbabwe than the knowledge that the global average temperature might rise by a few degrees. Local dynamics must be incorporated into any realistic and usable account of climate impacts.