Answer questions like ...

1. Since 1958, Arctic ice cover has lost how much of its thickness at the end of summer?
2. "Albedo" is a measure of an object's "brightness" — i.e., how much of the sunlight that hits the surface is reflected away. Which has a higher albedo?
3. Ice sheets are made of snow that builds up and gets compressed into ice, which then flows downhill toward the coast. What controls the mass of the Greenland and Antarctica ice sheets?

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