Cooperative Institute for Research in Environmental Sciences

Abstracts: 13

Cryospheric Change Detection: Examples from Various Data Sets

Richard Armstrong and Tingjun Zhang, Cryospheric and Polar Processes Division

The "cryosphere," which traces its origins to the Greek word kryos for frost or ice cold, collectively includes those portions of the earth system where water is in a solid form. Possibilities include sea ice, river and lake ice, glaciers, ice caps and ice sheets, ice shelves, permafrost, seasonally frozen ground and snow cover. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, precipitation, hydrology and atmospheric and oceanic circulation.

Global mean temperatures have risen over the past 100 years by about 0.6 C. Over half of this increase has occurred in the last 25 years. Polar and high-latitude regions are thought to be most sensitive to warming. In some regions, extreme warming has already been detected. Locations in Alaska and northern Eurasia, for example, have warmed by nearly 6.0 C in the winter months over the past 30 years. Many regions of the cryosphere are very sensitive to temperature change. Average temperatures in snow and ice-covered areas typically remain below 0 C much of the year. Unlike other substances found on Earth, ice and snow exist relatively close to their melting point and frequently change phase from solid to liquid and back again. Consequently, consistent and prolonged warming trends should result in observable changes to the Earth's cryosphere. Water changing from solid to liquid and back often results in dramatic visual changes across the landscape as various snow and ice masses shrink or grow.

In this phase of our ongoing study of the state of the cryosphere we investigate changes in snow cover, frozen ground, sea ice, glaciers and the related parameter sea level. Various forms of remote sensing allow the monitoring of snow, ice and frozen ground at varying spatial scales over the most recent 25 to 35 years. Results presented here focus on long-term monitoring of snow cover and frozen ground, but also include examples from other components of the cryosphere. In terms of spatial extent, frozen ground and snow cover represent the largest components of the cryosphere with a mean maximum areal extent exceeding 50 million km2, equivalent to about one half the land surface area of the Northern Hemisphere. In most all cases, regardless of parameter or measurement method, the amount of snow, ice and frozen ground has been decreasing over the past several decades.