Pronounced and unavoidable impacts of low-end global warming on northern high-latitude land ecosystems
Arctic ecosystems are particularly vulnerable to climate change because of Arctic amplification.Here, we assessed the climatic impacts of low-end, 1.5 °C, and 2.0 °Cglobal temperature increases above pre-industrial levels, on thewarming of terrestrial ecosystems in northern high latitudes (NHL, above 60 °N including pan-Arctic tundra and boreal forests)under the framework of the Inter-Sectoral ImpactModel Intercomparison Project phase 2b protocol.We analyzed the simulated changes of net primary productivity, vegetation biomass, and soil carbon stocks of eight ecosystemmodels that were forced by the projections of four global climatemodels and two atmospheric greenhouse gas pathways (RCP2.6 andRCP6.0). Our results showed that considerable impacts on ecosystem carbon budgets, particularly primary productivity and vegetation biomass, are very likely to occur in theNHL areas. Themodels agreed on increases in primary productivity and biomass accumulation, despite considerable inter-model and inter-scenario differences in themagnitudes of the responses. The inter-model variability highlighted the inadequacies of the presentmodels, which fail to consider important components such as permafrost andwildfire. The simulated impacts were attributable primarily to the rapid temperature increases in theNHL and the greater sensitivity of northern vegetation towarming, which contrastedwith the less pronounced responses of soil carbon stocks. The simulated increases of vegetation biomass by 30–60 PgC in this century have implications for climate policy such as the Paris Agreement. Comparison between the results at twowarming levels showed the effectiveness of emission reductions in ameliorating the impacts and revealed unavoidable impacts forwhich adaptation options are urgently needed in theNHL ecosystems.