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

• Main Authors: Mudryk, Lawrence, Santolaria-Otín, Maria, Krinner, Gerhard, Ménégoz, Martin, Derksen, Chris, Brutel-Vuilmet, Claire, Brady, Mike, Essery, Richard
• Format: Text
• Language: English
• Published: 2020
• Subjects: Ice; permafrost; Sea ice
• Online Access: https://doi.org/10.5194/tc-2019-320; https://tc.copernicus.org/preprints/tc-2019-320/

This paper presents an analysis of observed and simulated historical snow cover extent and snow mass, along with future snow cover projections from models participating in the 6th phase of the World Climate Research Programme Coupled Model Inter-comparison Project (CMIP-6). Where appropriate, the CMIP-6 output is compared to CMIP-5 results in order to assess progress (or absence thereof) between successive model generations. An ensemble of six products are used to produce a new time series of northern hemisphere snow extent anomalies and trends; a subset of four of these products are used for snow mass. Trends in snow extent over 1981–2018 are negative in all months, and exceed −50 × 103 km 2 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, which is valid across all scenarios. 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.