Ice

This chapter introduces the concept of the ‘cryosphere’ to help us understand the crucial role of water, locked up as ice, on the entire planet’s ecology. Glaciers, ice sheets, sea ice and permafrost combine to regulate our global temperature and sea level, and distribute fresh water to Earth’s habitats. Glaciers and ice sheets hold 70% of the planet’s fresh water, and are dynamic entities acutely sensitive and malleable to temperature and gravity. Sea ice is yet more delicate, with a maximum thickness of just a few centimeters – a product of its intimate relationship to the seasons that govern growth and melting. Permafrost occupies vast areas of the arctic northern hemisphere, and has a soft ‘active layer’, melting and refreezing as the seasons change, making it less ‘permanent’ than the name implies. Placing Earth’s climate history in a geological context, the chapter highlights that we are currently experiencing a relatively warm interglacial period, which ramped up roughly 10,000 years ago. Nevertheless, the last century has seen a marked spike in temperatures, the effects of which the icy world is particularly vulnerable to. Enhanced satellite observation has shown the rapid retreat of vast bodies of locked up water, e.g., the Greenland Ice Sheet, impacting ocean-circulation and methane release, and posing huge threats to world-wide, low-lying communities. The cryosphere is an impermanent, delicate system that must be protected by urgently addressing emissions, or risk being lost forever.