State shifts and divergent sensitivities to climate warming across northern ecosystems

Abstract Northern ecosystems are among the most exposed to warming and their responses are difficult to anticipate due to the variable sensitivity of their biophysical components. Using an analysis based on expert assessment, we investigated heterogeneity in the sensitivity to climate-driven state shifts across the vast northern landscape, from the boreal to the polar biomes. Over a 3,700 km latitudinal gradient in northeastern North America, we identified 28 discontinuous states for six ecosystem components: permafrost, peatlands, lakes, snowpack, vegetation, and endothermic vertebrates. Sensitivities were quantified by the estimated time required to shift from an initial to a contrasting state in response to a 5°C step increase in mean annual air temperature. The inferred scenario reveals that multiple interconnected state shifts are likely to occur within a narrow subarctic latitudinal band at timescales of 10 to >100 years. However, response times decrease with latitude, with freshwater systems at high latitudes displaying heightened susceptibility to rapid state shifts (timescales of 1 to 10 years). The lack of coherence in response times between components and across latitudes will likely impair the integrity of northern ecosystems and generate heterogeneous range shifts, resulting in the reconfiguration of landscapes and ecosystems.