Why has the Arctic sea ice minimum not set a new record in over 10 years?

The Arctic sea ice extent reached its annual minimum on September 10 at about 4.6 million km2. This is the 10th lowest value in the 47 years of satellite data since 1979, continuing the trend towards values significantly lower than the average sea ice extent in the 1980s, 1990s, and 2000s. Sea ice is particularly low this year along parts of the Siberian coast and in the Beaufort Sea off the coast of Alaska.

What is remarkable about this year’s sea ice minimum is that it is the 13th year in a row where there has not been a new record minimum — despite ongoing Arctic warming. The current record is still held by the year 2012 when the sea ice extent was as small as 3.3 million km2, substantially lower than any year before but also after. While the long-term trend in Arctic sea ice is still clearly downwards, the recent “slowdown” is well visible in the record (see Figure 1).

This is surprising since, after all, global temperatures have risen by over 0.3°C just since the year 2012. Recently, scientists have even voiced concerns that global warming is accelerating as humans continue to emit carbon while simultaneously cleaning up sun-reflecting particles from air pollution.

Now, in a new study, researchers have established that such a slowdown in sea ice loss in a warming climate is unusual but not dramatically so. Using computer models, they calculated that the chance to see such a slowdown is about 20% and show that it can happen naturally due to the variations in the climate system that occur on top of the long-term trend. They even say that in some of their model simulations such slowdowns can persist for 20 years. Unfortunately, the longer the slowdowns, the steeper the sea ice decline when the natural climate variations eventually flip direction. The study is very clear that this is not a sign that climate change has stopped.

Natural or “internal” climate variations occur all the time and are well-studied. Sometimes the variations combine with climate change to accelerate or slow the decline in Arctic sea ice, but they don’t have the power to reverse it. Such variations are akin to the daily weather we experience, which acts on top of slower changes such as the season. For example, if you’re lucky this year, you still get to experience a nice summer-like day in October even as you would expect the weather to be fall-like. At the same time, you know that winter is inevitable. 

Among several possible reasons for the current slowdown, the researchers suggest that ocean currents that normally transport warm water into the Arctic happened to be weaker during the last decade, temporarily offsetting some of the ice loss from rising air temperatures. 

The reprieve in ice loss is only a small piece of good news for polar bears that depend on sea ice as their habitat. Sea ice has also been thinning continuously, making ice — even if it’s there — less ideal for bears to walk on. Ultimately, unless humans stop emitting carbon, the world will continue to warm and eventually melt all Arctic sea ice, thereby endangering the animals and communities dependent on it.