Are we still living in an ice age?

Yes, by the geologists' definition we are. An ice age is any long stretch of time when Earth carries big continental ice sheets and polar ice caps, and Greenland and Antarctica are still covered in them. For most of its history Earth had little or no permanent ice, but it has been in its current ice age, the Late Cenozoic Ice Age, for 34 million years. What we call 'the ice age' is just its latest cold snap.

Inside an ice age, the climate swings between colder glacials, when ice sheets spread, and milder interglacials, when they shrink back. For the past few million years these swings have come every 40,000 to 100,000 years, paced by slow wobbles in Earth's orbit and tilt. The last big freeze peaked between 26,000 and 20,000 years ago. Since 11,700 years ago we have been enjoying a warm interglacial, the Holocene.

The idea started with ordinary people puzzling over boulders. In the Swiss Alps, locals believed their valleys had once been filled with ice, and in 1815 a chamois hunter called Jean-Pierre Perraudin pointed a geologist to scratched rocks and giant stranded boulders as proof. The geologist called it absurd. Two decades later the theory had a name, the 'ice age', and it took until the 1870s for scientists worldwide to accept it.