In this study, the period that corresponds to the thresholds of a 1.5 ℃ rise (relative to 1861 - 1880) in surface temperature is validated using a multi-model ensemble mean from 17 global climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). On this basis, the changes in permafrost and snow cover in the Northern Hemisphere are investigated under a scenario in which the global surface temperature has risen by 1.5 ℃, and the uncertainties of the results are further discussed. The results show that the threshold of 1.5 ℃ warming will be reached in 2027, 2026, and 2023 under three Representative Concentration Pathways (RCP2.6, RCP4.5, RCP8.5) respectively. When the global average surface temperature rises by 1.5 ℃,the southern boundary of the permafrost will move 1°-3.5° northwards, particularly in the southern Central Siberian Plateau. The permafrost area will be reduced by 3.43*10~6 km~2 (21.12%), 3.91 * 10~6 km~2 (24.10%) and 4.15*10~6 km~2 (25.55%) relative to 1986-2005 in RCP2.6, RCP4.5 and RCP8.5, respectively, under a scenario of 1.5 °C warming. The snow water equivalent will decrease in over half of the regions in the Northern Hemisphere but increase only slightly in the Central Siberian Plateau. The snow water equivalent will decrease significantly (more than 40% relative to 1986-2005) in central North America, western Europe and northwestern Russia. The permafrost area in Qinghai-Tibet Plateau will decrease by 0.15*10~6 km~2 (7.28%), 0.18*10~6 km~2 (8.74%), and 0.17*10~6 km~2 (8.25%), respectively, in RCP2.6, RCP4.5, RCP8.5. The snow water equivalent in winter (DJF) and spring (MAM) over the Qinghai-Tibet Plateau will decrease by 14.9% and 13.8%, respectively.