Key risks associated with projected climate trends for the 21st-century include the prospects of future climate states with no current analog and the disappearance of some extant climates. Novel 21st-century climates may promote formation of novel species associations and other ecological surprises, whereas the disappearance of some extant climates increases risk of extinction for species with narrow geographic or climatic distributions and disruption of existing communities. Here we analyze multi-model ensembles for the A2 and B1 emission scenarios produced for the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC AR4), with the goal of identifying regions projected to experience 1) high magnitudes of local climate change, 2) development of novel 21st-century climates, and/or 3) disappearance of extant climates. Novel climates are projected to develop primarily in the tropics and subtropics, whereas disappearing climates are concentrated in tropical montane regions and the poleward portions of continents. Under the high-end A2 scenario, 12-39% and 10-48% of the earth's terrestrial surface may respectively experience novel and disappearing climates by 2100 AD. Corresponding projections for the low-end B1 scenario are 4-20% and 4-20%. Dispersal limitations increase the risk that species will experience the loss of extant climates or the occurrence of novel climates. The strong concentration of disappearing climates in tropical regions previously identified biodiversity hotspots poses a serious challenge to conservation biologists; for these regions, standard conservation solutions (e.g. assisted migration, networked reserves) may be insufficient to preserve biodiversity.