11.4 Cryosphere changes: ice sheets, glaciers, and sea ice

Ice sheets and glaciers are undergoing significant changes due to global warming. Greenland and Antarctica are losing mass, contributing to sea level rise. These changes are driven by surface melting, ice-ocean interactions, and shifting glacier dynamics.

Sea ice in the Arctic is declining rapidly, while Antarctic sea ice shows complex regional patterns. These cryosphere changes impact global climate through albedo feedback, affect ocean circulation, drive sea level rise, and disrupt local communities reliant on ice-covered environments.

Ice Sheets and Glaciers

Changes in polar ice sheets

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• Greenland ice sheet experiencing significant mass loss since the 1990s due to increased surface melting and ice discharge contributing ~0.8 mm/year to global sea level rise
• Antarctic ice sheet losing mass primarily in the West Antarctic Ice Sheet (WAIS) from increased ice discharge caused by ice shelf thinning and collapse adding ~0.4 mm/year to sea level
• Combined, Greenland and Antarctica account for about one-third of the observed global sea level rise since 1993 (satellite era)

Mechanisms of ice retreat

• Surface melting accelerates as increased air temperatures lead to more melting on the ice surface which can penetrate and lubricate the base speeding up ice flow (moulins, supraglacial lakes)
• Ice-ocean interactions drive retreat as warming ocean waters melt the undersides of floating ice shelves causing thinning and collapse which reduces buttressing and allows glaciers to flow more rapidly into the ocean (Pine Island Glacier, Thwaites Glacier)
• Glacier dynamics change due to:
  1. Increased ice flow velocities from changes in basal conditions
  2. Reduced ice shelf buttressing
  3. Tidewater glaciers retreating as they calve more icebergs into the ocean (Columbia Glacier)

Sea Ice Changes and Implications

Trends in polar sea ice

• Arctic sea ice declining in extent and thickness since the 1970s with summer minimum extent decreasing ~13% per decade transitioning towards younger, thinner ice cover
• Antarctic sea ice showed slight overall increase in extent from 1979 to 2014 followed by a rapid decline with regional variability of decreases in the Amundsen and Bellingshausen Seas and increases in the Ross Sea impacted by atmospheric and oceanic circulation patterns making changes less clear than the Arctic

Impacts of cryosphere changes

• Global climate impacted as ice loss reduces the albedo leading to increased absorption of solar radiation and further warming (ice-albedo feedback) while changes in freshwater input from melting ice can affect ocean circulation patterns (AMOC slowdown)
• Sea level rise driven by melting land ice (ice sheets and glaciers) directly contributing to rise along with thermal expansion of ocean water due to warming
• Local communities impacted by:
  • Coastal flooding and erosion risks increasing due to sea level rise (Miami, Venice)
  • Arctic communities affected by changes in sea ice impacting transportation, hunting, and traditional livelihoods (Inuit, Yupik)
  • Glacial retreat altering water resources affecting agriculture, hydropower, and water supply for downstream communities (Andes, Himalayas)