To maximize outcomes of our proposed inter-disciplinary approach, we propose research within the context of specific landscape factors that are critical determinants of thaw effects, targeting regions that are poised for the most immediate and greatest change. Intensive, site-based studies indicate that four factors—permafrost continuity, ice content, soil morphology, and topography (Fig. 1) determine the susceptibility, rate, and hydrologic and biogeochemical consequences of thaw4. The resolution and certainty of spatial and vertical data availability for these factors is however hugely variable. Future research focused on improving resolution and certainty of these factors will be critical for making robust predictions of thaw impacts across broad spatial scales.

Permafrost continuity influences soil permeability, flowpaths, and residence times of water. This factor also affects the quantity, composition, and age of mobilized carbon, together determining its ultimate fate. We have a poor understanding of permafrost extent, and its vertical distribution (i.e. depth to permafrost and total thickness) in regions of active thaw and in discontinuous terrains at depths > 1 m. This is particularly important because in these regions we expect the largest spatial heterogeneity in depth to permafrost, which determines hydrological connectivity upon thaw, as well as the potential exchange of water and solutes above and below permafrost.

Ice content also critically determines the type and rate of thaw, and accompanying shifts in permeability. Ice-poor soils with low thermal inertia may be more vulnerable to gradual thaw over larger spatial scales and release mostly dissolved constituents. Ice-rich soils, however, are prone to abrupt thaw and surface collapse predominantly releasing particulate constituents11,12. While localized, these abrupt processes may become regionally recognized through aggregation of localized occurrences as ubiquity increases11. Relatively poor information on ground ice content at the pan-arctic scale currently limits the accuracy of quantitative projections of region-specific thaw rates2 and thermokarst potential.

Soil composition and morphology are also important. This factor regulates permeability, which in turn affects water and solute fluxes, and transit times. Soil composition and age13 determine the constituent leaching yield14, the degree of mineral sorption of organic material, and molecular structure of the organic matter—factors that affect the quantity and fate of carbon that is liberated. Information on soil composition is, however, mostly confined to the 0–3 m depth range3, resulting in uncertainty in quantifying hydrological and biogeochemical consequences of evolving flowpaths and talik formation in degrading, deeper, permafrost.

Finally, topography (i.e. relief) is a forcing factor that regulates response to thaw, superimposed on intrinsic properties described above. Topography affects the long-term build-up of organic material and ground ice, while also influencing thermokarst development (landscape collapse when ice-rich permafrost thaws) and the potential for lateral transport of dissolved and particulate material. Greater relief generates greater hydraulic gradients which increases water fluxes, reduces transit time, and enhances the propensity for lateral carbon transport along the terrestrial–aquatic continuum. While a high-resolution Digital Elevation Model is recently available for land north of 60°N (www.pgc.umn.edu/data/arcticdem/), subsidence in thermokarst-susceptible regions may necessitate periodic updates.