Abstract
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.
Highlights
Over the last 100 years, global climate has warmed distinctly, with the global surface temperature increasing by 0.74 °C ± 0.18 °C between 1906 and 20054
Previous studies have demonstrated that the permafrost will degrade because of temperature rises caused by greenhouse gas (GHG) emissions, the likely extent of permafrost degradation under a particular risk-level threshold remains to be determined
The determination of the period that corresponds to the thresholds of 1.5 °C and 2 °C rise in temperature is different under different models or different Representative Concentration Pathway (RCP) scenarios (RCP4.5, 6.5 and 8.5)
Summary
Over the last 100 years, global climate has warmed distinctly, with the global surface temperature increasing by 0.74 °C ± 0.18 °C between 1906 and 20054. Anisimov and Nelson[8] investigated permafrost distribution in the NH using a frost index under a global mean temperature rise of 2 °C and doubling of CO2 levels Their projected permafrost extent was 18.34 × 106, 18.74 × 106 and 19.17 × 106 km[2], respectively, as obtained using the Geophysical Fluid Dynamics Laboratory (GFDL) model, the Goddard Institute for Space Studies (GISS) model and the United Kingdom Meteorological Office (UKMO) model. This study focuses on what degree or how large in extent would the permafrost degradation response be to global warming under global temperature rise at risk-level thresholds of 1.5 °C, perhaps a maximum threshold of 2 °C. This is an important issue to the global community and is helpful for making adaptation and countermeasure policies
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