There's a general feeling that dynamic vegetation feedback may be necessary to get this right, but it's a subject that's much in flux. (realclimate.org)
In addition, they find that accounting for vegetation feedbacks leads to increased warming in summer at higher latitudes and a reduction in summer warming at lower latitudes. (pacificclimate.org)
Betts, R. A., Cox, P. M., Lee, S. E. & Woodward, F. I. Contrasting physiological and structural vegetation feedbacks in climate change simulations. (nature.com)