evidence: For hundreds of thousands of years, the Earth has gone through repeated cycles of warming and cooling. Roughly every hundred thousand years, there has been an ice age,1 driven by changes in the planet’s tilt and orbit that allowed less sunlight to reach the Arctic. Between these ice ages have been periods of warming. [...] But there are also key differences between the last significant period of warming and the modern day. First, today’s warming breaks from the historical cycle. In fact, before human-caused warming began, scientists believe the Earth was roughly due to enter a cooling cycle (although research to confirm this is ongoing).2 [...] Get the latest from Ask MIT Climate monthly in your inbox 1 The term "ice age" can be used in different ways. In some contexts, scientists use this term to refer to five very long periods of the Earth’s history when there has been ice at the poles. By this definition, we’re still in an ice age today! We’re just in an "interglacial period" of our ice age, when the planet is somewhat warmer and glaciers have retreated closer to the poles. In casual conversation, though, "ice age" usually refers to the colder "glacial periods" when ice has descended further south—including the most recent "ice age" when mammoths and saber-toothed tigers roamed the Northern Hemisphere.