Shifts in Arctic vegetation and associated feedbacks under climate change

Climate warming has led to changes in the composition, density and distribution of Arctic vegetation in recent decades1–4. These changes cause multiple opposing feedbacks between the biosphere and atmosphere5–9, the relative magnitudes of which will have globally significant consequences but are unknown at a pan-Arctic scale10. The precise nature of Arctic vegetation change under future warming will strongly influence climate feedbacks, yet Earth system modelling studies have so far assumed arbitrary increases in shrubs (for example, +20%; refs 6,11), highlighting the need for predictions of future vegetation distribution shifts. Here we show, using climate scenarios for the 2050s and models that utilize statistical associations between vegetation and climate, the potential for extremely widespread redistribution of vegetation across the Arctic. We predict that at least half of vegetated areas will shift to a different physiognomic class, and woody cover will increase by as much as 52%. By incorporating observed relationships between vegetation and albedo, evapotranspiration and biomass, we show that vegetation distribution shifts will result in an overall positive feedback to climate that is likely to cause greater warming than has previously been predicted. Such extensive changes to Arctic vegetation will have implications for climate, wildlife and ecosystem services. Vegetation productivity in Arctic ecosystems has increased over the past few decades, resulting in a trend of greening that is coincident with increases in Arctic surface air temperatures, which have risen at approximately twice the global rate12. Continued greening over the next century will produce multiple climate feedbacks. For instance, expansion of woody shrubs and trees into the tundra biome will act as a positive feedback to climate warming through increased surface net short-wave radiation associated with reductions in albedo due to taller and darker canopies5. Higher rates of evapotranspiration associated with woody vegetation will increase atmospheric water vapour concentrations, causing a second positive feedback to regional atmospheric heating6,8. Locally, shading associated with increasing shrub canopy covermay reduce soil temperatures, potentially slowing carbon release due to permafrost degradation and thus acting as a negative feedback to climate warming7. We estimate the influence of future climate-change predictions on the distribution of Arctic vegetation types using machinelearning, multi-class, ecological niche models13 implemented at relatively fine spatial resolution (4.5×4.5 km cells) and with Arctic