Historical Northern Hemisphere snow cover trends and projected changes in the CMIP-6 multi-model ensemble

Abstract:

Six observation-based products were used for trend analysis of historical Northern Hemisphere snow extent and snow mass, and to evaluate historical simulations from models participating in the 6th phase of the World Climate Research Programme Coupled Model Inter-comparison Project (CMIP-6). Trends in snow extent over 1981-2018 are negative in all months, and exceed -50 000 km2/yr during November, December, March, and May; snow mass trends are approximately -5 Gt/year or more for all months from December to May. Overall, the CMIP-6 multi-model ensemble better represents the snow extent climatology over the 1981-2014 period for all months, correcting a low bias in CMIP-5. Simulated snow extent and snow mass trends over the 1981-2014 period are slightly stronger in CMIP-6 than in CMIP-5, although large inter-model spread remains in the simulated trends for both variables. There is a single linear relationship between projected spring snow extent and global surface air temperature (GSAT) changes, valid across all CMIP6 Shared Socioeconomic Pathways. This finding suggests that Northern Hemisphere spring snow extent will decrease by about 8% relative to the 1995-2014 level per °C of GSAT increase. The sensitivity of snow to temperature forcing largely explains the absence of any climate change pathway dependency, similar to other fast response components of the cryosphere such as sea ice and near surface permafrost.