To establish the most effective conservation strategies, we must understand the ecological dynamics of the systems that we are trying to conserve. But we do not know the extent to which plants and animals shift their ranges in response to changing climates. Using the fossil pollen and mammal records, we explore how rapidly biomes transition in response to changing climates and to what extent human impacts prevent species from tracking their preferred climate. We have found that plants and animals will need to traverse broad landscapes at unprecedented rates to track climate as it changes, and I have identified strategic regions to target for facilitating this connectivity. However, we also have found that not all species exhibit the same human tolerance or climate fidelity (i.e., some species’ ranges are less affected by climate than others). My lab and I found that 67% of mammals have shifted their climatic niche, mostly in the last 500 years. Interestingly many small mammals have actually expanded their climatic niches into agricultural and urban landscapes, suggesting that humans facilitate their survival. Whereas most large mammals have been extirpated from human-impacted landscapes. We are now working to identify the climate fidelity that plant and animal taxa have exhibited over the last 20,000 years. Our goal is to identify the types of species whose climate tracking we must prioritize as we identify efficient and effective connectivity strategies.