An integrated index of cryospheric change in the Northern Hemisphere

The cryosphere plays an important role in the earth system and has experienced a dramatic and rapid decline due to climate change. Most cryospheric research focuses on changes in individual components, but there is no single metric that quantifies the cryosphere as a whole. We initially investigate 17 parameters representing various cryospheric components, and ultimately use principal component analysis on 13 of these variables to define an integrated index that quantifies cryospheric changes. Based on its strong negative correlation with air temperatures, we reconstruct the cryospheric index back to 1850, and also project it to 2100 using different climate model scenarios. An overall decrease is found in the cryospheric index, with interdecadal variability: an increase during 1940–1970, a subsequent strong decrease during the recent 50 years, and a projected fast decline in the future. We assess the associations between the cryospheric index and vegetation, greenhouse gases, and sea level rise. This cryospheric index represents an important new indicator of cryospheric and climatic change, that will be useful to compare against changes in other environmental variables.