Glacier Time Machine: Advance, Retreat and Sea Level
Understand a glacier as a budget: snow added above the snow line minus ice melted below it. A positive balance makes it advance, a negative one makes it retreat, and the meltwater ends up in the sea.
Before you try
What if summers were 3 °C warmer? How long would a 8 km glacier last?
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What happened?
Move a control to see what changes and why.
One glacier with a simple length response and a fixed melt rate per degree; the sea-level figure is an illustrative scaling, not a forecast.
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Try these ideas
- Run the Today preset for 50 years and note the retreat.
- Find the warming at which the balance is exactly zero for the default snowfall.
- Run the Little Ice Age preset and see how far the glacier advances.
Why it works
A glacier is a river of ice that flows slowly downhill. High up, more snow falls each year than melts, and it packs down into ice; lower down, melting wins. The boundary is the snow line. If the glacier gains more than it loses over a year it advances; if it loses more it retreats, even though the ice never stops flowing. Warmer summers move the snow line up the valley and tip the balance toward loss.
The Himalaya holds thousands of glaciers that feed the Ganga, Indus and Brahmaputra in the dry season, and most are shrinking. Meltwater from land ice raises sea level worldwide. In this simulator you set the yearly snowfall and the summer warming, run the years, and see the front advance or retreat and the sea-level contribution grow. Presets recreate the Little Ice Age, today, and a high-warming 2100.
Check your understanding
Question 1 of 4
A glacier retreats when
Warmer summers move the snow line
Melting which of these raises sea level?
Why do Himalayan glaciers matter for people far away?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Compare old and new photographs of a glacier such as Gangotri.
- Ask: if a glacier stops retreating, has the climate stopped warming?
- Melt an ice cube in a full glass of water and see whether it overflows.