Climatology of Northern Hemisphere Cryo‐cover

Abstract

AbstractThe Earth's cryo‐cover (defined here as snow cover and sea ice) is dynamic, and varies considerably on both interannual and seasonal time‐scales. This study analyzes trends in Northern Hemisphere cryo‐cover from 1979 to 2020 using three datasets: National Snow and Ice Data Center (NSIDC) Sea Ice Extent, Rutgers Global Snow Lab (GSL) Snow Cover Extent and MeaSuREs State of the Cryosphere values. Temporal trends of cryo‐cover, both as a combined variable and as separate snow and ice components, are calculated on an annual and monthly basis. Using derived cryo‐cover concentration values, pixels are categorized to be either stable (covered 75% of the time or more) or transient (covered <75% of the time), as a method to differentiate the type of cryo‐cover present annually and monthly as well as associated trends and transitions from one cover type (stable or transient) to the other. Results indicate a decrease in cryo‐cover since 1979 with sea ice decreasing in all months, but snow cover increasing in the autumn and early winter and decreasing during the spring. Decreasing trends in stable cryo‐cover are observed during most months with several months seeing increases in transient cover. Increases in autumn snow cover (particularly in October) help to offset the large decreases in late summer/early autumn sea ice. From April to August, cryo‐cover as a whole exhibits statistically significant decreasing trends. A comprehensive understanding of the climatology of cryo‐cover is of great importance in understanding the radiative impacts of a changing cryosphere in a warming climate.