Glaciers and Polar Ice: Why They Are Melting and Why It Matters

Remember from earlier grades

In Grade 7 geography you learned that the Athabasca Glacier in the Rockies is shrinking, and in Grade 7 science you learned how greenhouse gases cause the enhanced greenhouse effect. Now you will explain why ice is melting and what that does to water systems near you and around the world.

Walking to a glacier

At the Columbia Icefield in the Rocky Mountains, markers along the trail to the Athabasca Glacier show where the edge of the ice used to be in different years. Walking from the oldest markers to today's edge, visitors cross a long stretch of bare rock that was once under ice. The Athabasca Glacier has pulled back more than 1.5 km in about 125 years and has lost more than half its volume.

Kinds of ice on Earth

• Glaciers form where more snow falls in winter than melts in summer. Year after year, the snow is pressed into dense ice. When it is thick enough, it flows slowly downhill. Valley glaciers fill mountain valleys (Rockies, Coast Mountains, Yukon).
• Ice caps cover high land on Arctic islands, such as Baffin and Ellesmere islands in Nunavut.
• Ice sheets are the giants: Antarctica and Greenland. If all the Antarctic ice sheet melted, sea level would rise by about 58 m; Greenland's would add about 7 m. This would take many centuries or more, but even a small fraction matters.
• Sea ice is frozen seawater, floating on the Arctic Ocean, Hudson Bay and around Antarctica. It is usually 1 to a few metres thick. It grows each winter and shrinks each summer.

People often say polar ice caps to mean all the ice near the poles, both on land and floating.

Why is the ice melting? Factors

1. Warmer air from climate change. Extra greenhouse gases from burning fossil fuels trap more heat (the enhanced greenhouse effect). The Arctic is warming faster than the global average.
2. Warmer ocean water. Warmer seawater melts sea ice from below and melts the edges of ice sheets where they touch the ocean.
3. The albedo feedback loop. Fresh snow and ice reflect most sunlight (often around 80% or more). Open ocean and bare ground are dark and absorb most of it. When ice melts, dark water or rock is exposed, absorbs more energy, warms up, and melts more ice. This positive feedback is one reason the Arctic warms so fast.
4. Soot and dust. Tiny dark particles from burning (wildfires, diesel engines) land on snow and ice, lower its albedo and speed up melting.
5. Less snowfall in some places. A glacier shrinks if summer melting is greater than winter snowfall.

Natural factors also change ice over time. Slow changes in Earth's orbit caused the ice ages over tens of thousands of years, and big volcanic eruptions can cool Earth for a year or two. But scientists have found that natural factors cannot explain how fast ice is melting today. The main cause of today's warming is human-produced greenhouse gases.

Land ice vs. sea ice: which raises sea level?

• Sea ice is already floating. A floating object pushes aside (displaces) a weight of water equal to its own weight. When it melts, its water fills almost exactly the space it was displacing, so sea level barely changes. (Think of ice cubes melting in a glass: the glass doesn't overflow.)
• Land ice (glaciers and ice sheets) is on land. When it melts, the meltwater flows into the ocean as new water, so sea level rises.
• Thermal expansion: as ocean water warms, it expands, which also raises sea level.

Global average sea level has risen about 21 to 24 cm since 1880, and it is rising faster now than during the 1900s.

Effects on water systems

Global:

• Rising sea level floods low coasts, erodes shorelines and pushes salt water into coastal aquifers and rivers.
• Less Arctic sea ice. In September 2025, Arctic sea ice shrank to about 4.60 million km², tied for the 10th-lowest on record (NASA) and well below the 1981–2010 average. Less ice means more open, dark water (albedo feedback).
• Ocean changes. Fresh meltwater lowers the salinity of seawater near ice sheets, which can affect ocean currents that move heat around Earth.

In Canada and Ontario:

• Glacier-fed rivers. Rivers such as the Bow, which flows through Calgary, get part of their late-summer water from Rocky Mountain glaciers. As glaciers shrink, melting may first increase flow, but later there will be less water in late summer, when farms, towns and fish need it most.
• The North. Thinner sea ice that forms later and breaks up earlier makes travel on the ice less safe and less predictable for Inuit and other northern communities who use sea ice as roads and hunting grounds. Thawing permafrost damages buildings and roads and changes lakes and rivers.
• Hudson Bay. The ice now breaks up earlier in summer and forms later in fall than a few decades ago, so polar bears in the region have less time on the ice to hunt seals.
• Ontario's Great Lakes are not fed by glaciers today (they were carved by glaciers in the last ice age), but warming means less winter ice cover on the lakes in many years, which can increase evaporation and change lake-effect snow.