A Primer:

Sea Ice & Albedo Feedback

What makes the Arctic Ocean unique is its perennial cover of sea ice. The extent of coverage varies with the season. In winter, there is more sea ice and in summer, there is less. Sea ice is frozen ocean. It starts forming in the Fall when temperatures drop and the ocean cools. Then open water freezes into first-year ice. At the same time, sea ice that has survived the previous summer thickens. This older ice is called multiyear ice. At some point in the dark of winter, first-year and multiyear floes freeze into an essentially continuous floating ice sheet. In springtime the process is reversed. As the ocean warms, the ice floes melt. Eventually, under the action of wind, waves and current — bumping, grinding, drifting, melting — the ice pack breaks apart. At the end of summer, ice on the Arctic Ocean is at its lowest extent of year round coverage.

Historically, multiyear floes predominated in the Arctic Ocean, persisting through each year, shrinking in the summer and growing in the winter. This is changing. We are now witnessing a dramatic decrease in the amount of Arctic sea ice in all months of the year. And we are also seeing a decrease in the substance of that ice. First-year ice now predominates over multiyear ice, and vast expanses of open water exist in areas that were covered in sea ice less than a decade ago.

This prevailing trend of declining sea ice cover is tied to an atmospheric-oceanic mechanism referred to as ‘ice albedo feedback’. The concept of ice albedo is simple. When incoming solar energy from the sun hits white ice and snow, almost all of it gets reflected back to space. In contrast, dark ocean waters absorb sunlight. Incoming solar energy, absorbed by the open ocean, warms surface waters which causes the melting and shrinking of the sea ice cover. This exposes more surface waters, which leads to further warming and melting, a loop that feeds on itself. The more open water there is to absorb the sun’s rays, the faster the ice melts. As white ice switches over to dark open water, the Arctic darkens and its albedo is lessened. This phenomenon is what underscores the Arctic Ocean’s ever-increasing importance in today’s discourse on global climate. The Arctic Ocean has been losing sea ice much faster than scientists had predicted even a decade ago. These losses have profound implications for the earth’s climate, implications that are immediate. A recent Scripps Institution of Oceanography study determined that the impact of today’s Arctic sea ice declines on increasing global temperatures is at least 25% of the direct effect of carbon emissions. This is because, as sea ice disappears and the Arctic warms, the thermal balancing act between the northern and temperate latitudes is disrupted. That disruption has brought on further warming of the planet and has altered weather patterns across the world.

What makes the story of declining Arctic sea ice truly mind-blowing is the diminishing timescale: polar scientists agree that a summer day is soon arriving when the last Arctic ice floe will disappear. This is big. Why have we heard so little about it?