The phrase “ice age” usually conjures images of woolly mammoths and frozen plains. Those were specific times when ice covered much of the Northern Hemisphere. But scientifically, an “ice age” just means a period when there’s significant permanent ice somewhere on Earth - and by that definition, we’re technically still in one. The Arctic and Antarctic ice caps qualify.
The current ice age started about 2.6 million years ago and is called the Quaternary Ice Age. Within it, the climate has cycled between cold glacial periods (when ice sheets advance far south) and warmer interglacial periods (when they retreat back to the poles). We’re in an interglacial period right now - the last full glacial peak was about 20,000 years ago, when ice sheets covered Canada and much of Europe.
The cycles are driven by Milankovitch cycles - slow changes in Earth’s tilt, orbit shape, and axial wobble that cause subtle but persistent changes in how much sunlight reaches the planet. Combined with feedback loops in ocean and atmosphere, these orbital variations make ice sheets grow and shrink over tens of thousands of years. Geologists have now documented dozens of these glacial/interglacial cycles in the rock and ice core record.
