The Moving Map

Earth's climate zones are not fixed. Play a time-lapse across millions of years and you would watch them crawl across the globe. During the Eocene epoch, the planet was so warm it was essentially ice-free. Crocodile relatives basked in the Arctic, and forests grew in Antarctica. The map of "hot" and "cold" looked nothing like today's.

Then run the clock forward. At the Last Glacial Maximum about 20,000 years ago, ice sheets buried most of Canada and northern Europe under crushing weight. Yet only 6,000 years ago the Sahara was a green, lake-dotted savanna — the African Humid Period. Zones don't just nudge a little. They can turn a desert into grassland and a forest into ice.