Arctic Climate Change: Sensitivities to the Forcing Scenario in CMIP6

Abstract:

While it is well known that the Arctic is a bellwether of global climate change, the future trajectory of Arctic change is highly sensitive to the forcing scenario. The ongoing Phase 6 of the Coupled Model Intercomparison Project (CMIP6) includes scenarios, from the low-end SSP1-2.6 with net negative CO₂ emissions by 2100 and the high-end SSP5-8.5 in which mitigation measures are relatively weak. Late-summer (September) sea ice stabilizes at more than half its present value under SSP1-2.6, while the Arctic Ocean’s sea-ice extent falls below the “ice-free” threshold of 1 million square kilometers by 2100 under the other scenarios. Late-winter (March) ice extent ranges from 8.5 to about 14 million square kilometers under the SSP1-2.6 and SSP5-8.5 scenarios, respectively, but with large across-model variability. Under scenarios of global warming that stabilize at 2.0°C and 1.5°C, the Arctic Ocean warms by 5-7°C and 3-5°C, respectively. Northern Hemisphere spring snow cover stabilizes in both of these cases, but with a reduced extent under the 2°C global warming. We also present results on the occurrence of extremes events under the various future scenarios, showing how SSP1-2.6 is the only scenario in which frequencies stabilize at close to present-day values.