Chapter 3

Melting Sea Ice, Glaciers, and Permafrost

The most visible signs of Arctic warming are the rapid loss of sea ice, the retreat of glaciers, and the thawing of permafrost. These three elements are closely connected and form the foundation of the Arctic environment. Their transformation is not only reshaping the polar landscape but also influencing global climate, ecosystems, sea levels, and human societies.

Scientists consider the Arctic one of the world’s most sensitive climate regions because even small increases in temperature produce dramatic changes in ice and frozen ground. Satellite observations, field measurements, and climate models all show that the Arctic is undergoing profound physical changes that are occurring faster than many researchers expected only a few decades ago.

Understanding Arctic Sea Ice

Sea ice forms when the surface of the Arctic Ocean freezes during the long winter. Unlike glaciers or ice sheets, sea ice floats on the ocean and constantly grows, drifts, fractures, and melts with the changing seasons.

Each autumn, falling temperatures cause seawater to freeze. Throughout the winter, the ice expands across millions of square kilometers. In spring and summer, warmer temperatures and increased sunlight cause much of this ice to melt. This natural seasonal cycle has existed for thousands of years, but climate change has dramatically altered its balance.

Today, the Arctic is losing sea ice at an unprecedented rate. Summer sea ice covers a much smaller area than it did just a few decades ago, and the remaining ice is generally thinner and younger. Thick multi-year ice, once common across the Arctic Ocean, has become increasingly rare.

Why Sea Ice Matters

Sea ice performs many essential functions within Earth’s climate system.

First, it reflects a large portion of incoming solar radiation back into space. This reflective property helps regulate global temperatures by preventing excessive heat absorption.

Second, sea ice acts as an insulating barrier between the relatively warm ocean and the cold Arctic atmosphere. Without this barrier, more heat escapes from the ocean into the air, contributing to regional warming.

Third, sea ice provides habitat for a wide variety of organisms. Tiny algae grow beneath the ice and form the base of the Arctic marine food web. Fish feed on these algae, seals feed on fish, and polar bears hunt seals. Many seabirds also rely on sea ice for feeding and resting.

Finally, sea ice influences ocean circulation, weather systems, and the exchange of heat and moisture between the ocean and atmosphere.

Declining Sea Ice Extent

Since continuous satellite monitoring began in 1979, scientists have documented a steady decline in Arctic sea ice extent, particularly during late summer when melting reaches its maximum.

The shrinking ice cover has several important consequences.

More open water absorbs additional sunlight, warming the ocean.

Warmer ocean water delays the formation of new ice during autumn.

Thinner ice melts more easily the following summer.

This creates a powerful positive feedback loop that accelerates Arctic warming.

Climate models suggest that under high greenhouse gas emission scenarios, the Arctic Ocean may experience nearly ice-free summers before the end of the twenty-first century. Although winter sea ice will continue to form, summer ice is expected to become increasingly scarce.

Changes in Sea Ice Thickness

Sea ice thickness is just as important as its extent.

Historically, much of the Arctic Ocean was covered by thick multi-year ice that survived several summers. Some of this ice exceeded four meters in thickness and could resist melting during warm years.

Today, much of this has been replaced by first-year ice, which is thinner, weaker, and more vulnerable to melting.

Thinner ice breaks apart more easily during storms, allowing warm ocean water to mix upward and accelerate further melting.

This transformation has reduced the Arctic’s resilience to rising temperatures.

Melting Glaciers

Glaciers are large masses of ice that slowly flow downhill under their own weight. They form over thousands of years as snowfall accumulates faster than it melts.

The Arctic contains thousands of glaciers located in Alaska, northern Canada, Greenland, Iceland, Norway, Russia, and many Arctic islands.

As air temperatures rise, glaciers lose more ice through surface melting and by calving, a process in which large blocks of ice break off into the ocean.

Nearly every major Arctic glacier has retreated during recent decades.

Many smaller glaciers are disappearing entirely.

The loss of glaciers affects freshwater supplies, river ecosystems, tourism, and regional biodiversity.

Greenland Ice Sheet

The Greenland Ice Sheet is the second-largest body of ice on Earth, surpassed only by Antarctica. Covering approximately 1.7 million square kilometers, it stores enough frozen water to raise global sea levels by about seven meters if it were to melt completely.

Fortunately, such complete melting would require many centuries or even millennia under current climate projections. However, Greenland is already losing hundreds of billions of tons of ice each year.

Ice loss occurs through two main processes.

Surface melting increases during warmer summers.

Large outlet glaciers discharge icebergs into the surrounding ocean.

Together, these processes make Greenland one of the largest contributors to current global sea-level rise.

Scientists carefully monitor the ice sheet using satellites, aircraft, GPS measurements, and ground observations to better understand how rapidly it is changing.

Icebergs and Ocean Changes

As glaciers flow into the sea, they produce icebergs of many different sizes.

These floating ice masses gradually melt, releasing freshwater into the Arctic Ocean and the North Atlantic.

Large inputs of freshwater can influence ocean salinity, circulation patterns, and marine ecosystems.

Scientists continue studying how increasing freshwater from Greenland may affect major ocean currents that help regulate climate across Europe and North America.

Permafrost: Frozen Ground Beneath the Surface

Permafrost refers to ground that remains frozen for at least two consecutive years. In many Arctic regions, permafrost has remained frozen continuously for thousands of years.

It can extend from a few meters to several hundred meters below the surface.

Permafrost underlies vast areas of Alaska, Canada, Greenland, Scandinavia, and Siberia.

Within this frozen ground are enormous quantities of ancient plant material that never fully decomposed because of extremely low temperatures.

This organic matter contains immense amounts of carbon that have been locked away for millennia.

Thawing Permafrost

As Arctic temperatures rise, permafrost begins to thaw.

When frozen soil warms above freezing, microorganisms become active and begin decomposing ancient organic matter.

This decomposition releases greenhouse gases into the atmosphere.

In oxygen-rich soils, carbon dioxide is produced.

In waterlogged soils with little oxygen, methane is released.

Methane is especially significant because it traps far more heat than carbon dioxide over shorter time periods.

Although the exact future rate of emissions remains uncertain, thawing permafrost represents one of the most important long-term climate feedbacks.

Landscape Changes

Permafrost thaw transforms Arctic landscapes in many ways.

Ground that was once solid becomes unstable.

Hillsides collapse.

Roads crack.

Buildings tilt.

Pipelines shift.

Railways deform.

Airstrips develop uneven surfaces.

Entire forests may sink as ice-rich soils melt beneath them.

These dramatic land changes are known as thermokarst, a landscape characterized by collapsing ground, ponds, and irregular terrain.

Thermokarst landscapes are becoming increasingly common across northern regions.

Effects on Rivers and Lakes

Permafrost influences how water moves through Arctic landscapes.

As frozen ground thaws:

• River channels may change.
• Lakes may drain suddenly.
• New wetlands may form.
• Water quality may change.
• Sediment transport increases.

These changes affect fish populations, drinking water supplies, and freshwater ecosystems.

Coastal Erosion

Many Arctic coastlines consist of frozen soil held together by permafrost.

As temperatures rise:

• Sea ice no longer protects shorelines from waves.
• Stronger storms strike exposed coasts.
• Thawing permafrost weakens cliffs.
• Coastal erosion accelerates.

Some Arctic communities now face relocation because their coastlines are disappearing into the sea.

Impacts on Wildlife

Ice loss affects nearly every Arctic species.

Polar bears depend on sea ice to hunt seals. As hunting seasons become shorter, bears must swim longer distances and spend more time on land, reducing access to their primary food source.

Walruses use sea ice as resting platforms between feeding trips. Reduced ice forces thousands of animals onto crowded beaches, where stampedes can cause injuries and deaths.

Ringed seals build snow dens on stable sea ice to protect their pups from predators and harsh weather. Earlier melting reduces the survival of newborn seals.

Marine birds, whales, Arctic foxes, fish, and countless smaller organisms are also affected as habitats change and food webs shift.

Global Sea-Level Rise

One important distinction is that melting sea ice does not directly raise sea level because it already floats in the ocean.

However, melting glaciers and ice sheets on land do contribute to sea-level rise.

As more land ice melts:

• Ocean levels gradually increase.
• Coastal flooding becomes more frequent.
• Storm surges become more destructive.
• Saltwater intrudes into freshwater supplies.
• Low-lying islands and coastal cities face increasing risks.

Even modest increases in sea level can have major consequences for millions of people living near coastlines.

Monitoring Arctic Ice

Scientists employ a wide range of technologies to observe changes in Arctic ice and frozen ground.

These include:

• Earth-observing satellites
• Laser altimeters
• Radar imaging
• GPS stations
• Ocean buoys
• Research aircraft
• Icebreaker expeditions
• Drone surveys
• Ground temperature sensors
• Automatic weather stations

These tools provide continuous data that improve climate models and help researchers understand how rapidly the Arctic is changing.

Looking Ahead

The future of Arctic sea ice, glaciers, and permafrost depends largely on global greenhouse gas emissions. Reducing emissions can slow the rate of warming, preserving more summer sea ice, limiting glacier loss, and reducing long-term permafrost thaw. Conversely, continued high emissions are expected to accelerate these changes, with consequences that extend far beyond the Arctic.

The disappearance of ice and frozen ground is more than a symbol of climate change—it is a powerful driver of further warming, rising sea levels, ecosystem disruption, and economic challenges. Understanding these interconnected processes is essential for preparing for a changing world.

In the next chapter, we will examine how Arctic warming is affecting wildlife and ecosystems, exploring the remarkable species that inhabit the far north and the challenges they face in an increasingly warmer environment.