The science of Arctic melting

Since North-West Passage exploration began over 400 years ago the polar ice caps have started to melt due to global warming.

In 2007 satellite images revealed that the North-West Passage – the seaway through the Arctic linking the Atlantic and Pacific Oceans – was, for the first time since records began, sufficiently ice-free for large ships to pass through the Arctic. However, the route is still hazardous and varies year on year. This makes it impractical for international shipping, which relies on tight schedules.

How has the ice melted?

Earth's polar ice caps, which are made of water ice desalinated by the freezing process, go through a cycle of melting in the summer and freezing in the winter. There is less ice in the polar ice caps today than there was 400 years ago, when North-West Passage exploration began, because human activity is heating up the Earth. This is known as the greenhouse effect.

What causes the greenhouse effect?

Certain gases in the Earth’s atmosphere absorb heat that rises from the surface, acting like a worldwide blanket. It is useful that they do this. Without greenhouse gases the world would be considerably cooler (by 20–30°C) and much less hospitable. The most common greenhouse gases are carbon dioxide (CO2) and methane (CH4).

However, since the Industrial Revolution of the 18th and 19th centuries human activity has been rapidly increasing the amount of greenhouse gases entering the atmosphere. Burning fossil fuels like coal and oil releases carbon dioxide. Cattle passing wind generate huge quantities of methane. At the same time many of the world’s forests, which play a vital role in absorbing greenhouse gases are being cut down. The theory is that the ‘blanket’ around the planet is therefore getting ‘thicker’ as it accumulates more greenhouse gases, causing the Earth to get hotter.

Why is the ice melting so fast?

One theory that accounts for this incredibly rapid decline in ice is explained by the concept of ‘positive feedback’. Seawater absorbs heat from the Sun, but ice (being white) reflects the Sun’s rays back into space. As the ice decreases there is more seawater to absorb the heat and less ice to reflect it away, accelerating the overall warming process.

What impact does Arctic melting have?

Arctic wildlife has been deeply affected by the changes occurring in their habitats. For instance, the retreat of sea ice has reduced the opportunities for seals and walruses to rest between their searches for food. Caribou and polar bears now fall through ice that was once solid, and have less access to food.

For humans, melting permafrost (soil that stays at or below the freezing point of water) has destroyed the foundations of houses, eroded shorelines and forced people, such as the Native Canadian Inuit, to move inland. This is also dangerous because it releases more greenhouse gases from the ground.

Are there any positives?

Ironically, the future opening up of the North-West Passage to shipping may offer one tiny benefit to the environment. Commercial shipping is a major global contributor to CO2 emissions (more so than even aviation), so the shorter sea routes provided by the North-West Passage could significantly reduce emissions.

Find out more about North-West Passage exploration