We’re living in an ice age right now!
Sandy Eldredge and Bob Biek 19 [Eldredge is a retired geologist, Biek received his B.A. in Geology from the University of California at Berkeley in 1983 and a M.S. in Geology from Northern Illinois University in 1987, “GLAD YOU ASKED: ICE AGES – WHAT ARE THEY AND WHAT CAUSES THEM?”, September 2019, https://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/]//rurallion
An ice age is a long interval of time (millions to tens of millions of years) when global temperatures are relatively cold and large areas of the Earth are covered by continental ice sheets and alpine glaciers. Within an ice age are multiple shorter-term periods of warmer temperatures when glaciers retreat (called interglacials or interglacial cycles) and colder temperatures when glaciers advance (called glacials or glacial cycles).
At least five major ice ages have occurred throughout Earth’s history: the earliest was over 2 billion years ago, and the most recent one began approximately 3 million years ago and continues today (yes, we live in an ice age!). Currently, we are in a warm interglacial that began about 11,000 years ago. The last period of glaciation, which is often informally called the “Ice Age,” peaked about 20,000 years ago. At that time, the world was on average probably about 10°F (5°C) colder than today, and locally as much as 40°F (22°C) colder.
What causes an ice age and glacial-interglacial cycles?
Many factors contribute to climate variations, including changes in ocean and atmosphere circulation patterns, varying concentrations of atmospheric carbon dioxide, and even volcanic eruptions. The following discusses key factors in (1) initiating ice ages and (2) the timing of glacial-interglacial cycles.
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One significant trigger in initiating ice ages is the changing positions of Earth’s ever-moving continents, which affect ocean and atmospheric circulation patterns. When plate-tectonic movement causes continents to be arranged such that warm water flow from the equator to the poles is blocked or reduced, ice sheets may arise and set another ice age in motion. Today’s ice age most likely began when the land bridge between North and South America (Isthmus of Panama) formed and ended the exchange of tropical water between the Atlantic and Pacific Oceans, significantly altering ocean currents.
Glacials and interglacials occur in fairly regular repeated cycles. The timing is governed to a large degree by predictable cyclic changes in Earth’s orbit, which affect the amount of sunlight reaching different parts of Earth’s surface. The three orbital variations are: (1) changes in Earth’s orbit around the Sun (eccentricity), (2) shifts in the tilt of Earth’s axis (obliquity), and (3) the wobbling motion of Earth’s axis (precession).