Future Climate Scenarios for California: Freezing Isoclines, Novel Climates, and Climatic Resilience of California’s Protected Areas

Twenty-first century climate change threatens biodiversity, ecosystem services, and human welfare. The diversity of responses and climate sensitivity among species and ecosystems presents a challenge for forecasting, conservation, and resource management. This paper explores several biotically informed analyses of current climates and future climate projections for California, and their implications for biological conservation. Section 1 examines shifts in the distribution of freezing events, mapping areas that are no longer projected to experience freeze events of various magnitudes by the end of the twenty-first century; whereas, they have experienced freezes in the past. These areas may be sensitive to vegetation shifts, as plants that are not cold tolerant expand their ranges northward and to higher elevations. Section 2 examines expanding, novel, shrinking, and disappearing climates of California, based on the areal extent occupied by different combinations of climatic conditions. Under more severe climate change scenarios, large areas of the desert and Central Valley regions may experience expanding and novel climates, while conditions along the coast and in the High Sierra are forecast to shrink in extent, and in some cases disappear. Such analyses provide a general framework for forecasting impacts of climate change on species and vegetation types that occupy these regions. Section 3 examines the climatic heterogeneity of California's protected area network, encompassing State and National Parks, National Forests, and other public and private conservation lands. Climatic heterogeneity is expected to enhance conservation in the twenty-first, promoting diversity of species that tolerate different conditions and allowing for dispersal along climate gradients in response to climate change. Large reserves, especially those spanning broad elevational gradients, are critical to encompass a broad range of present and future climates. These results highlight the value of large, connected areas for conservation in the face of climate change.