National Park Service U. S. Department of the Interior Natural Resource Program Center

Summary conclusions

The influence of human activities on the climate system, primarily through increased greenhouse gases and aerosol concentrations, will be superimposed on natural drivers of climatic change. As records of the past and model projections for the future suggest, our certainty about the patterns of climate change varies widely. Temperatures will most likely increase over large spatio-temporal scales, but the patterns and direction of change in other climatic variables are less clear. Investigating past change also instructs us that, at smaller spatio-temporal scales, changes in future climatic conditions will likely vary greatly, especially in heterogeneous mountain environments characterized by steep biophysical gradients. Temperatures are predicted to increase in the ensuing decades, making much of the western United States vulnerable to increased frequency and duration of drought (Barnett et al. 2008; Seager et al. 2007; Diffenbaugh et al. 2005). Small increases in temperature (e.g., 1–2ºC, 2–4°F) will require large increases in precipitation to offset increased evapotranspiration, especially in settings where increased temperatures significantly alter available moisture and surface-energy feedbacks (Hoerling and Eischeid 2007).

High levels of uncertainty about how ecosystems will respond to changing conditions should not prevent managers from planning for the future. Scenario planning can be an effective approach for considering a wide range of possible future conditions that oftentimes indicate similar management actions. In many ways, the outcomes of scenario planning reinforce fundamental principles of adaptive resource management. For example, management practices that focus on maintaining diversity, increasing connectivity, providing buffer habitat around protected areas, and mediating human impacts within and around public lands will also facilitate the dynamic and heterogeneous redistribution of vegetation that will likely occur across the West.

Paleoenvironmental records suggest that ecosystems are responsive to climatic change over millennial to decadal time and spatial scales, but they also suggest that we should anticipate novel vegetation assemblages as species respond individualistically to climate change and communities reorganize (Whitlock et al. 2003; MacDonald et al. 2008; Williams et al. 2007; Jackson et al. 2009b). These changes also suggest that natural disturbances, non-native species, disease, and unforeseen synergistic interactions will be associated during periods of ecological disequilibrium. Management actions that work to accommodate dynamic and difficult to predict redistributions of vegetation by protecting a full suite of biophysical and environmental gradients, increasing connectivity, and minimizing human impacts in landscapes surrounding protected areas may best protect valuable resource attributes in the face of climate change.

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