When ice covered Canada
Imagine standing where Toronto, Winnipeg or Montreal is today and seeing nothing but ice, up to 3 km thick, stretching to the horizon. About 20 000 years ago, that’s what almost all of Canada looked like. This was the peak of the last glacial period of the current ice age.
What is an ice age?
An ice age is a long period, lasting millions of years, when Earth is cold enough to have large ice sheets on land. Within an ice age, the climate swings between:
| Period | Description |
|---|---|
| Glacial period | Colder; ice sheets grow and advance |
| Interglacial period | Warmer; ice sheets shrink and retreat |
Surprisingly, we’re living in an ice age right now! Greenland and Antarctica still have huge ice sheets. We’re in a warm interglacial period called the Holocene, which began about 11 700 years ago.
Earth has had at least five major ice ages in its history. The current one began about 2.6 million years ago.
The last glacial period
At its peak, about 21 000 to 19 000 years ago:
- Ice sheets covered about a quarter of Earth’s land.
- The Laurentide Ice Sheet covered most of Canada and reached south to where New York and Chicago are today.
- The Cordilleran Ice Sheet covered the mountains of BC and Yukon.
- So much water was locked in ice that sea level was about 120 m lower than today.
- Global average temperatures were about 6 °C colder than today.
The Bering land bridge
With lower sea levels, a wide land bridge called Beringia connected Asia and North America. Animals and, many scientists think, some of the first people to reach the Americas crossed this region. Parts of Yukon and Alaska stayed ice-free and were home to woolly mammoths, steppe bison and other animals.
What causes glacial periods?
Milankovitch cycles
In the 1920s and 1930s, Serbian scientist Milutin Milanković calculated that regular changes in Earth’s orbit affect how much sunlight reaches the Northern Hemisphere in summer. These are called Milankovitch cycles.
| Cycle | What changes | About how long |
|---|---|---|
| Eccentricity | The shape of Earth’s orbit (more or less oval) | 100 000 years |
| Obliquity | The tilt of Earth’s axis (22.1° to 24.5°) | 41 000 years |
| Precession | The wobble of Earth’s axis | About 23 000 years |
When northern summers are cool, snow doesn’t fully melt. It builds up year after year, forming ice sheets.
Feedbacks
Small changes are amplified:
- Ice reflects sunlight. More ice reflects more sunlight, making Earth even colder.
- Carbon dioxide: during glacial periods, oceans absorbed more CO₂, reducing the greenhouse effect.
How do we know?
| Evidence | What it tells us |
|---|---|
| Ice cores | Air bubbles trapped in Antarctic and Greenland ice record temperature and CO₂ going back 800 000 years |
| Landforms | U-shaped valleys, moraines, drumlins and erratics show where glaciers were |
| Ocean sediments | Tiny shells record past ocean temperatures |
| Fossils | Remains of cold-adapted animals far south of where they live today |
| Pollen | Shows which plants grew where |
Ice age animals
The last glacial period was home to giant animals, called megafauna:
| Animal | Notes |
|---|---|
| Woolly mammoth | Thick fur; long curved tusks; well-preserved remains found frozen in Yukon permafrost |
| Woolly rhinoceros | Shaggy coat; two horns |
| Giant beaver | About the size of a black bear, found in Canada |
| Sabre-toothed cat | Long fang-like canine teeth |
| Short-faced bear | One of the largest meat-eating land mammals |
| American mastodon | Elephant relative; browsed in forests |
In 2022, gold miners in Yukon discovered a nearly complete baby woolly mammoth, named Nun cho ga by the Tr’ondëk Hwëch’in First Nation.
Many of these animals went extinct about 13 000 to 10 000 years ago, probably due to climate change and human hunting.
How the ice age shaped Canada
As the ice melted, it left behind:
- the Great Lakes and thousands of other lakes
- huge glacial lakes like Lake Agassiz, which once covered much of Manitoba
- fertile soils on the Prairies
- boulders called erratics scattered across the land
- rolling hills called drumlins and long ridges called eskers
The land is still rising in places like Hudson Bay, rebounding after being pressed down by the weight of the ice.
Ice ages and today
Today’s climate is warming much faster than at the end of the last glacial period, mostly because of greenhouse gases from human activity. Studying past ice ages helps scientists understand how sensitive Earth’s climate is.
Common mistakes
- Thinking the ice age is over. Technically, we’re in a warm interglacial within an ice age.
- Thinking ice ages were constantly frozen. Climate swung between colder and warmer periods.
- Thinking dinosaurs lived in the ice age. They died out about 66 million years ago, long before.
Try it yourself
- Freeze sand and pebbles in water in a yogurt container. Rub the ice block across clay and observe the scratches.
- Find a landform near you that was shaped by glaciers.
- Make a timeline from 25 000 years ago to today showing the ice sheets melting.
Quick recap
- An ice age is a long cold period with large ice sheets; glacial and interglacial periods alternate.
- We’re in a warm interglacial period of an ice age that began 2.6 million years ago.
- About 20 000 years ago, ice up to 3 km thick covered most of Canada.
- Milankovitch cycles and feedbacks drive glacial periods.
- Ice cores, landforms and fossils record the ice age.