Glacial period

• 1. Introduction

  ›

  About 15,000 years ago, glacial period ended and the world that modern humans would build their civilizations on began to emerge. Vast ice sheets that had buried Northern Europe as far south as northern Germany started their slow retreat. The rivers, valleys, and coastlines that feel permanent and ancient today were freshly carved.

  But that ending was not a singular event. It was one chapter in a much longer story of cycles, a rhythm of freeze and thaw stretching back millions of years. What drives those cycles? How many times has the ice returned? And what does the future hold for a planet now warming rapidly from within its own atmosphere? Those are the questions this documentary will answer.

• 2. What a Glacial Period Is

  ›

  A glacial period is an interval, measured in thousands of years, within a broader ice age, marked by falling temperatures and advancing glaciers. It is not the same thing as an ice age itself. An ice age is the larger framework; a glacial period is a cold pulse within it.

  Between those cold pulses come interglacials, stretches of warmer climate when the ice retreats and conditions soften. The Holocene, the epoch humanity currently occupies, is one such interglacial. A world with no glaciers anywhere on Earth represents an even warmer baseline, what scientists call a greenhouse climate state. The planet has visited all of these conditions across deep time, cycling through them in patterns driven by forces far larger than any single generation can observe.

• 3. The Quaternary Rhythm

  ›

  The Quaternary Period began about 2.6 million years before the present, and within that span the planet has passed through a number of glacials and interglacials. In the last 740,000 years alone, at least eight full glacial cycles have occurred.

  Changes in atmospheric composition and associated shifts in how much solar energy the planet retained were among the primary drivers of these climate swings. Ocean circulation, biological productivity, and the acid-base chemistry of seawater likely accounted for most of the recorded fluctuations within those broad swings. Across the last 650,000 years, the average pattern works out to roughly seven cycles of glacial advance and retreat, a figure that conveys just how regular, and yet how incomplete, our picture of this rhythm still is.

• 4. The Penultimate Glacial

  ›

  Before the most recent ice advance, the planet endured what scientists call the Penultimate Glacial Period. It began about 194,000 years ago and ran until approximately 135,000 years ago, when the climate warmed into the Eemian interglacial.

  The Eemian was a period of relative warmth, a window between two great cold episodes. The Penultimate Glacial Period demarcates one boundary of that warm window, and its close marks the kind of transition that left its signature in sediment cores, ice cores, and fossilized pollen around the world. Each glacial period ends not with a clean break but with a gradual warming that reshapes coastlines, ecosystems, and the distribution of species across continents.

• 5. The Last Glacial Period

  ›

  The Last Glacial Period began about 110,000 years ago and ended about 11,700 years ago, making it the most recent glacial episode within the broader Quaternary glaciation. At its peak, known as the Last Glacial Maximum around 26,500 years before the present, ice sheets covered enormous portions of the Northern Hemisphere.

  Geographers and geologists in different regions gave the same ice advance different names based on where they studied it. In North America it became the Wisconsin; in Great Britain, the Devensian; in Ireland, the Midlandian; in the Alps, the Wurm; in northern Central Europe, the Weichsel. Chinese researchers named regional expressions after specific localities: Dali in East China, Beiye in North China, Taibai in Shaanxi, and others in Sichuan and the Tian Shan. In the Himalayas the advance bore the name of the mountain now called Everest, rendered in Tibetan script as Jomolungma. In South America, the Llanquihue glaciation marked the ice's reach into Chile. In Europe, the ice sheet pushed as far south as northern Germany before the slow retreat began that would eventually give way to the Holocene.

• 6. A Warm Future, Perhaps

  ›

  Because the orbital mechanics that drive glacial cycles are predictable, scientists can run climate models forward as well as backward. Work by Berger and Loutre suggests the current warm period may persist for another 50,000 years even without human influence.

  Greenhouse gases now being released into the atmosphere and oceans may push that figure further still, potentially delaying the next glacial period by an additional 50,000 years beyond what orbital mechanics alone would produce. That is a striking reversal of the planet's long rhythm. For millions of years, glaciations arrived on their own schedule. The possibility that human emissions could suppress an entire glacial cycle points toward just how significantly the atmosphere's chemistry can alter the planet's most fundamental climate patterns.