ice age

How Did the Ice Age Happen?

Steve Russell - August 15, 2023

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Few movies are as thrilling as disaster films set during a coming ice age — breathtaking images of modern Earth freezing over as the fittest among humanity scramble to survive. No amount of technological advancements and preparations seem enough to protect society in these storylines. 

Movies like these leave audiences questioning whether they would survive a new ice age and if one is possible in today’s climate. Indeed, global warming would stop a deep freeze in its tracks, wouldn’t it? 

Of course, one must also ask, “How did the ice age happen?” to understand if we’ll see another in our lifetime. Surprisingly, climatic changes may actually be the trigger.

What Caused the Ice Age?

An ice age isn’t an overnight occurrence, taking tens of hundreds of thousands of years to transpire. When summer temperatures stay below freezing in the northern hemisphere, winter snow and ice accumulate. Eventually, it compresses and compacts into an ice sheet. 

It could then take another few thousand years for ice sheets to expand. Historically, this starts in northern Canada before reaching across the globe — yet scientists have also discovered past glaciation in Scandinavia.

Overall, global temperatures were about 4° Celsius cooler millions of years ago than today’s average temperatures. However, evidence indicates carbon dioxide in the atmosphere triggers cooling and heating. Additionally, ice ages are likely associated with the Milankovitch cycle, in which a 25% variation in the Earth’s tilt and orbit determines whether it receives less solar radiation during the summer — a factor out of our control entirely.

Greenhouse gases and CO2 levels are also significant players in developing freezing ice age temperatures and warmer interglacial periods. Studies show temperatures fell half as much as Antarctic temperatures during the last ice age — meaning it only takes slight climate fluctuations to trigger a freeze event.

Ice Ages Throughout Earth’s History

You may have heard people differentiate the first and last ice ages, but scientists know of at least five significant events. The earliest geological record is of the Huronian ice ages between 2.4 and 2.1 billion years ago, possibly resulting from changes in microbial life. 

Two additional glacial periods followed during the Cryogenian era, lasting nearly 20 million years each. The end of these ice ages occurred with the evolution of more complex life forms on Earth, sparked by altering ecological conditions.

The Cenozoic glacial period was much warmer from 66 million years ago to today. The early years indicated the end of dinosaurs as life evolved again. By the Oligocene Epoch — 34–23 million years ago — temperatures began to cool and Antarctic ice sheets expanded rapidly to North America and Europe. 

The Pleistocene Epoch — 2.6 million to 10,000 years ago — had fluctuating temperatures of 10° C every 100,000 years. We are currently within an interglacial period since 11,000 years ago when the last ice age peaked.

The Last Ice Age

The last ice age occurred about 20,000 years ago when ice sheets enveloped North America, South America, Europe and Asia. According to one study, temperatures were nearly 6.1° C — or 11° Fahrenheit — cooler than today’s. Conditions were also drier, with far less precipitation and lower sea levels. 

History’s largest mammals — mammoths, mastodons, saber tooth tigers and wooly rhinos — existed during the last ice age. By the end of the era, most of the “Megafauna” went extinct — likely a culmination of hunting by early humans and ecological changes.

Climate Change and Future Ice Ages

According to a recent study, Antarctic icebergs — that drift long distances before melting — have kickstarted previous ice ages. The redistribution of freshwater into ocean water has been a significant factor. 

Global oceanic circulation patterns shift during redistribution, leading to more CO2 being pulled from the atmosphere and absorbed into the ocean. As a result, it limits the greenhouse effect and sends the Earth spiraling into freezing conditions.

Glaciers and ice sheets store 68.7% of the planet’s freshwater. Scientists believe a mass melting would increase sea levels by 200 feet globally. Meanwhile, if the Greenland Ice Sheet alone were to melt, the sea level would rise to 24.3 feet.

Albeit a frightening thought, we may have postponed the sixth ice age for a few thousand — or hundred thousand — years. No one can be sure how the altered climate will change the outcome. Due to human activity, fossil fuel emissions are six times higher than during the last solar cycle — and will continue heating the planet regardless. It’s difficult to determine how detrimental the effects would actually be.

Implications of Another Ice Age

Nevertheless, it’s not unusual to wonder what will happen to society when that day comes. The entertainment industry has undoubtedly filled our imaginations with many possibilities. Would any of us be capable of surviving the sixth ice age?

Ice sheets would begin forming in the northern hemisphere — Scandinavia, Russia and Antarctica — as Himalayan ice sheets would spread throughout Asia. 

Those living in coastal communities with ocean views will have to relocate hundreds of miles for their waterfront landscape. As the ocean freezes, sea levels would decrease by 394 feet, making the Mediterranean and Atlantic oceans inaccessible. New land bridges would then form, bringing countries closer together, forcing borders to change and causing mass migrations as societies rush to more habitable regions. 

Humans survived the last ice age by wearing fur and hunting large animals. In the future, we will lose most of our agricultural lands due to less precipitation, meaning intense competition for essential resources will exist. You can expect great unrest as people try to protect themselves and their families. 

Survival will be challenging — however, humans have done it once before and can do it again. Fortunately, a sixth ice age isn’t going to happen in our lifetime and certainly not in our children’s or grandchildren’s either.

Ice Ages Are a Natural Occurrence

Humans did not cause ice ages in the past — in fact, we didn’t even exist during the first. Ice ages occurred naturally due to temperature fluctuations and the Earth’s orbit patterns. The question of whether human activity and climatic changes would impact future ice ages remains. Of course, it isn’t something we must worry about any time soon.

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About the author

Steve Russell

Steve is the Managing Editor of and regularly contributes articles related to wildlife, biodiversity, and recycling. His passions include wildlife photography and bird watching.