As we watch glaciers around the world recede, we sometimes hear the argument that these changes are part of the Earth’s natural fluctuation. But the fact is we’ve been in a relatively stable and warm period for at least 15,000 years. And we are unnaturally making the Earth even warmer. Before that, ice ages covered most of the Northern Hemisphere with glaciers.
The last of the five major ice ages, called the Pleistocene glaciation, began about 1.5 million years ago. It is thought to be caused in part by the Earth getting less of the sun’s warming radiation — because of the pull of other planets in our solar system.
The Pleistocene glaciation contained at least 20 ice fluctuations within it, in which ice advanced and receded. Sometimes, up to 30% of Earth was covered in ice.
At times this included the better part of North America — California became almost completely entombed in ice. Today, evidence of the glacial takeover can be found as far down as southern California’s San Bernardino Mountains.
GIF From Cosmos: A Spacetime Odyssey, The Lost Worlds Of Planet Earth
When this ice age ended 15,000 to 25,000 years ago, the Earth entered an interglacial warm period. This is the period that we live in today and the climate that allowed modern humans to begin our worldwide colonization.
NOW WATCH: Briefing videos
Business Insider Emails & Alerts
Site highlights each day to your inbox.