Forecasts of species range shifts under climate change most often rely on ecological niche models, in which characterizations of climate suitability are highly contingent on the species range data used. If ranges are far from equilibrium under current environmental conditions, for instance owing to local extinctions in otherwise suitable areas, modelled environmental suitability can be truncated, leading to biased estimates of the effects of climate change. Here we examine the impact of such biases on estimated risks from climate change by comparing models of the distribution of North American mammals based on current ranges with ranges accounting for historical information on species ranges. We find that estimated future diversity, almost everywhere, except in coastal Alaska, is drastically underestimated unless the full historical distribution of the species is included in the models. Consequently forecasts of climate change impacts on biodiversity for many clades are unlikely to be reliable without acknowledging anthropogenic influences on contemporary ranges.

气候变化下物种范围变化的预测最常依赖生态位模型，其中气候适应性的表征高度取决于所使用的物种范围数据。如果当前环境条件下的范围远未达到平衡，例如由于在其他合适地区的局部灭绝，则建模的环境适应性可能会被截断，从而导致对气候变化影响的估计有偏差。在这里，我们通过比较基于当前范围的北美哺乳动物分布模型与解释物种范围历史信息的范围，来研究这种偏见对气候变化估计风险的影响。我们发现，除了阿拉斯加沿海地区以外，几乎所有地方的估计未来多样性 除非模型中包括了该物种的完整历史分布，否则将大大低估该值。因此，如果不认识到人为因素对当代范围的影响，对气候变化对许多进化枝对生物多样性的影响的预测就不太可能可靠。