Executive Summary

The cryosphere, comprising snow, river and lake ice, sea ice, glaciers, ice shelves and ice sheets, and frozen ground, plays a major role in the Earth's climate system through its impact on the surface energy budget, the water cycle, primary productivity, surface gas exchange and sea level. The cryosphere is thus a fundamental control on the physical, biological and social environment over a large part of the Earth's surface. Given that all of its components are inherently sensitive to temperature change over a wide range of time scales, the cryosphere is a natural integrator of climate variability and provides some of the most visible signatures of climate change.

Since AR4, observational technology has improved and key time series of measurements have been lengthened, such that our identification and measurement of changes and trends in all components of the cryosphere has been substantially improved, and our understanding of the specific processes governing their responses has been refined. Since the AR4, observations show that there has been a continued net loss of ice from the cryosphere, although there are significant differences in the rate of loss between cryospheric components and regions. The major changes occurring to the cryosphere are as follows.