The Climate Crisis: There's No Going Back
© WWF-US / Chris Conner
A Disappearing World
The Science of Sea Ice

Seen from space, the Earth is a blue marble with a frosting of ice at either end. But closer up, the Arctic and Antarctic are very different worlds. DAVID MILLAR explains the history of sea ice and what the future may hold for it as the planet warms.

THE ANTARCTIC HAS a permanent ice sheet several kilometres deep, whereas the Arctic is an ocean covered by a thin layer of floating ice only a few metres thick. The critical consequence of this difference is that ice in the Arctic is far more fragile and dramatically more susceptible to the warming effects of the climate crisis. Also, unlike Antarctic land ice, Arctic sea ice varies with the seasons, growing each winter and shrinking each summer.

Drone photo of melting iceberg, Scoresby Sound, Greenland.
© Annie Spratt / Unsplash


Both poles developed their current ice covers around 50 million years ago. By 13 million years ago, the Arctic sea ice had become perennial. However, it has varied over the years: two to three million years ago, it was considerably thicker than it is today—several hundred metres thick—although it has waxed and waned with the climate since then. As recently as 125,000 years ago, the area may have been almost ice-free, but for the last 5,500 years, there has been ice year-round.

However, the situation has changed dramatically over just the past few decades. Prior to the 1980s, at least half of the Arctic Ocean was ice-covered, even at the height of summer. But in recent years, the proportion has been as low as 28 per cent—and it is getting smaller every year. The ice is thinner, too, with very little “multi-year” ice— that is, ice thick enough not to melt completely in the summer and instead builds year over year.

Therefore, what is unique about the current situation is not so much the reduction in sea-ice extent, but the speed at which the ice has disappeared. We know there were big changes in the past, but they took thousands of years to occur. Today we are looking at an Arctic that will likely be completely icefree in fewer than 50 years if we don’t take immediate action. The speed of this change reflects the different causal mechanism—not slow-moving natural phenomena, as before, but the short, sharp shock of human-made change.

Although the ice of the Arctic Ocean is floating, its surrounding islands and land masses have year-round land-based ice. In some places, such as Ellesmere Island in Nunavut, Canada, it can reach thicknesses of hundreds of metres. But land ice is also melting. Some of the smaller ice caps have disappeared completely. (Fortunately, this generally has far less impact on ecosystems because fewer animals live or hunt on them.) Nonetheless, Greenland is currently melting at a rate of more than 200 cubic kilometres of ice per year, causing significant coastal erosion and reducing the salinity of the surrounding seas. Eventually, it may even have an impact on the Gulf Stream.

We know there were big changes in the past, but they took thousands of years to occur. Today we are looking at an Arctic that will likely be completely ice-free in less than 50 years if we don’t take immediate action.


There is no question that anthropogenic climate change will affect the Arctic. It is already happening and is dramatically altering its ecosystems and the Inuit way of life. The questions scientists are thinking about now focus on how much worse it will get, how quickly, and how far beyond the Arctic the impact will be felt. In some scenarios, the Arctic could essentially be entirely ice-free in the summers within five to 10 years. Its fate depends on choices the world is making now: for example, if the global temperature increase can be held to 1.5°C, the Arctic may be able to retain some summer sea ice. But if we lose sight of that goal, summer ice will vanish within decades.

© James Morgan / WWF-UK

This will devastate polar bear populations, given that the bears need sea ice to hunt. How will it affect sea populations and fisheries? Warmer waters could well improve fisheries. The impact on people in the North will clearly be significant, but how, exactly? Depending on one’s perspective, some of the likely changes, such as increased tourism and shipping and easier mining, could be positive economic developments. But at what cost to local wildlife, traditional ways of life, and global efforts to contain carbon emissions? We don’t have all the answers yet—but it may not be long before we experience the results of our choices.

DAVID MILLAR is a research associate with the Arctic Institute of North America in Canada.