There is ample evidence that 20thcentury warming has shifted ranges of temperate and arctic species, but on page 261 of this issue, Moritz et al. (1) provide an exceptionally thorough example: They take advantage of a well-documented study from a century ago (2) to demonstrate contractions and expansions of elevation range among small mammals in Yosemite National Park, California, USA. In contrast, there have been few attempts to even address the tropics’ sensitivity to global climate change (3). Also in this issue (page 258), Colwell et al. (4) use a novel conceptual approach to analyze climate shifts in tropical ecosystems.