2020, Ito, Akihiko, Reyer, Christopher P. O., Gädeke, Anne, Ciais, Philippe, Chang, Jinfeng, Chen, Min, François, Louis, Forrest, Matthew, Hickler, Thomas, Ostberg, Sebastian, Shi, Hao, Thiery, Wim, Tian, Hanqin

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 °C global temperature increases above pre-industrial levels, on the warming 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 Impact Model Intercomparison Project phase 2b protocol. We analyzed the simulated changes of net primary productivity, vegetation biomass, and soil carbon stocks of eight ecosystem models that were forced by the projections of four global climate models and two atmospheric greenhouse gas pathways (RCP2.6 and RCP6.0). Our results showed that considerable impacts on ecosystem carbon budgets, particularly primary productivity and vegetation biomass, are very likely to occur in the NHL areas. The models agreed on increases in primary productivity and biomass accumulation, despite considerable inter-model and inter-scenario differences in the magnitudes of the responses. The inter-model variability highlighted the inadequacies of the present models, which fail to consider important components such as permafrost and wildfire. The simulated impacts were attributable primarily to the rapid temperature increases in the NHL and the greater sensitivity of northern vegetation to warming, which contrasted with the less pronounced responses of soil carbon stocks. The simulated increases of vegetation biomass by 30–60 Pg C in this century have implications for climate policy such as the Paris Agreement. Comparison between the results at two warming levels showed the effectiveness of emission reductions in ameliorating the impacts and revealed unavoidable impacts for which adaptation options are urgently needed in the NHL ecosystems.

2019, Shiogama, Hideo, Hasegawa, Tomoko, Fujimori, Shinichiro, Murakami, Daisuke, Takahashi, Kiyoshi, Tanaka, Katsumasa, Emori, Seita, Kubota, Izumi, Abe, Manabu, Imada, Yukiko, Watanabe, Masahiro, Mitchell, Daniel, Schaller, Nathalie, Sillmann, Jana, Fischer, Erich M., Scinocca, John F., Bethke, Ingo, Lierhammer, Ludwig, Takakura, Jun’ya, Trautmann, Tim, Döll, Petra, Ostberg, Sebastian, Müller Schmied, Hannes, Saeed, Fahad, Schleussner, Carl-Friedrich

Clarifying characteristics of hazards and risks of climate change at 2 °C and 1.5 °C global warming is important for understanding the implications of the Paris Agreement. We perform and analyze large ensembles of 2 °C and 1.5 °C warming simulations. In the 2 °C runs, we find substantial increases in extreme hot days, heavy rainfalls, high streamflow and labor capacity reduction related to heat stress. For example, about half of the world's population is projected to experience a present day 1-in-10 year hot day event every other year at 2 °C warming. The regions with relatively large increases of these four hazard indicators coincide with countries characterized by small CO2 emissions, low-income and high vulnerability. Limiting global warming to 1.5 °C, compared to 2 °C, is projected to lower increases in the four hazard indicators especially in those regions.