Climate change already harming the global economy - environment - 26 September 2012 - New Scientist
I remain very skeptical that reliable economic modelling can possibly be done for the economic effects of global warming over the long term.
Just use common sense, and don't limit your thinking to some artificial target like the turn of the century.
I mean, can anyone reliably model the economic effects of eventual ocean level rise of (say) 3 metres over the course of 100 - 200 years? I would rather just assume that turning many centres of civilisation (known as "cities") into empty versions of Venice is a bad idea, and you do what you can now to reduce the possibility in as economically sound way as you can.