Most of the Northern Hemisphere Permafrost Remains under Climate Change.

Degradation of cryospheric components such as arctic sea ice and permafrost may pose a threat to the Earth's climate system. A rise of 2 °C above pre-industrial global surface temperature is considered to be a risk-level threshold. This study investigates the impacts of global temperature rises of 1.5 °C and 2 °C on the extent of the permafrost in the Northern Hemisphere (NH), based on the 17 models of Coupled Model Intercomparison Project Phase 5 (CMIP5). Results show that, when global surface temperature rises by 1.5 °C, the average permafrost extent projected under Representative Concentration Pathway (RCP) scenarios would decrease by 23.58% for RCP2.6 (2027-2036), 24.1% for RCP4.5 (2026-2035) and 25.55% for RCP8.5 (2023-2032). However, uncertainty in the results persists because of distinct discrepancies among the models. When the global surface temperature rises by 2 °C, about one-third of the permafrost would disappear; in other words, most of the NH permafrost would still remain even in the RCP8.5 (2037-2046) scenario. The results of the study highlight that the NH permafrost might be able to stably exist owing to its relatively slow degradation. This outlook gives reason for hope for future maintenance and balance of the cryosphere and climate systems.