Earth's Frozen Water
Understand the cryosphere, Earth's frozen parts, including snow, glaciers, ice sheets, sea ice and frozen ground. Glaciers, ice sheets and permanent snow store about 69% of Earth's fresh water. Trace snow and meltwater through the water cycle. Distinguish melting land ice, which adds ocean water, from melting floating sea ice. Complete melting of the Greenland and Antarctic ice sheets could raise average global sea level by more than 65 metres.
What a learner can do afterwards
- Define the cryosphere as Earth's frozen parts and name snow, glaciers, ice sheets, sea ice and frozen ground, including permafrost
- State that glaciers, ice sheets and permanent snow store about 69% of Earth's fresh water
- Trace snow and meltwater through the water cycle and explain the sea-level effects of melting land ice compared with floating sea ice
1 · Read
You have learned about glaciers and ice sheets. These belong to the cryosphere, Earth's frozen parts. Snow, sea ice and frozen ground belong too. Permafrost is ground that stays at or below 0 degrees Celsius for at least two years. It may contain ice, but soil and rock are not themselves frozen water. Ocean currents move liquid water.
69% means about 69 parts out of 100. That is more than all the other freshwater stores together. Not all the remaining water is easy to use. To find what remains in a model, subtract the stored amount from the total. If 7 of 10 counters represent ice, 10 minus 7 leaves 3 counters for other water.
Snow can build up into glacier ice. Meltwater can flow into rivers and the ocean. Liquid water can evaporate into vapour. As vapour cools, cloud droplets or ice crystals can form. Water falls as rain or snow, called precipitation. Snow can build up again. The cycle has no fixed beginning, and water may stay frozen for a long time.
This is one possible route. Not every drop follows the same path.
Melting land ice adds water to the ocean and raises sea level. Floating sea ice already pushes ocean water aside, so melting it has little direct effect on sea level. Complete melting of the Greenland and Antarctic ice sheets could raise average global sea level by more than 65 metres and flood many coastal places. This is a full-melt scenario, not a forecast for the next few years.
Land ice and floating sea ice affect sea level differently.
The cryosphere includes ice, snow and frozen ground. Most fresh water is stored as ice and snow. Meltwater joins the water cycle, and melting land ice raises sea level.
Lesson text, questions and flashcards written for this dataset.
The three readings were written for this dataset. Linked video: "When will the next ice age happen? - Lorraine Lisiecki", Lorraine Lisiecki, TED-Ed.
More to read
From snowfall to flowing water
A snowflake lands on a glacier. More snow covers it, and the layers may become glacier ice. Some of that ice may later melt. Water can travel through streams to the ocean, evaporate and eventually fall as snow again.
This is one possible route through the water cycle. Water may also remain in a glacier for a long time. Being stored as ice does not remove it from the cycle. The cryosphere contains water stores that change and connect with liquid water and water vapour.
Two ways the ocean can rise
Land ice stores water outside the ocean. When that ice melts and its water reaches the sea, the ocean gains water. Floating sea ice already pushes water aside, so its melting has little direct effect on sea level.
Ocean warming can also raise sea level. Warmer seawater takes up more space. Adding meltwater and expanding seawater are different processes.
The more-than-65-metre estimate concerns complete melting of the Greenland and Antarctic ice sheets. It does not say that this rise will happen in the next few years.
Measuring ice from space
Different satellite measurements answer different questions about ice. Changes in Earth's gravity help scientists estimate changes in the mass of ice sheets. Radar observations can help track glacier movement.
Researchers compare measurements made at different times. They can investigate how much ice has been lost and how quickly parts of a glacier are moving. These are related questions, but they are not identical.
A measurement of recent ice loss is also different from a forecast. Predicting future change requires more than extending one measurement forever.
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2 · Watch
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Where this leads
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.