What you will learn in Cryosphere, Glaciers and Ice Sheets

1. 1. Floating and grounded

   Two vessels, one block of ice in each. Melt the one that floats and the one that rests on a support, read the levels, and find out why the Arctic Ocean is not the sea-level story and Greenland and Antarctica are.

2. 2. A glacier is a budget

   Snow is the income, melt is the spending, and the glacier's length is what the budget can support. Warm a glacier and it retreats; warm it and feed it enough snow and it advances.

3. 3. Ice flows

   Ice deforms under its own weight like a very stiff fluid, and it can slide on its bed. The speed is greatest at the centre of the surface and least against the bed and the walls, and the surface cracks where the flow is stretched.

4. 4. Measuring ice

   Three agencies published three different sizes for the same Arctic minimum, and none of them is wrong. Extent is a measurement with a method attached: an instrument, an algorithm, a threshold, a grid and a day.

5. 5. Ice ages

   The orbit's three cycles change when and where sunlight arrives, and hardly change how much. Combine them, lay them against the glacial record, and find the forcing far too small on its own — and the 100 000-year rhythm still unexplained.

6. 6. What the ice remembers

   Drill into an ice sheet and every metre holds more years than the one above it. Read the layers, the isotopes, the trapped air and the volcanic sulphate, and see why the age of deep ice is a model as well as a count.