Arctic sea ice is extremely complex and comes in many forms that respond more or less aggressively to seasonal changes and temperature anomalies. Currents, wind patterns, and even subtle differences in Earth’s gravitation also influence sea ice extent, although temperature usually plays a dominant role. As a result, Arctic sea ice coverage rises in winter and falls in summer. Its minimum and maximum yearly extent reflect shifts in average annual temperature, and in turn climate change.
The sharp decline in Arctic sea ice coincided with very high global temperatures. In fact, scientists are still determining whether 2014 was actually warmer than 2010. In the wake of the winter of 2010/11, it seemed as though even the direst projections of Arctic sea ice decline had been too optimistic. Perhaps a threshold had been crossed, a tipping point had been reached, and Arctic sea ice would soon vanish.
If Arctic warming has persisted since 2010, why has Arctic sea ice recovered? One possible explanation lies in the recent history of the Arctic Oscillation (AO), a band of winds that circle the Arctic in a counter clockwise direction. When the AO is in a positive phase, its winds move quickly, tightly sealing frigid air in the Arctic. When it is in a negative phase, its winds move more slowly and the band is distorted, allowing Arctic air to descend towards lower latitudes. There appears to be a correlation between a negative AO and reductions in Arctic sea ice extent. The AO, which was in a strongly negative phase in 2010, is now apparently in a weakly positive setting.
Recent research also suggests that Arctic sea ice has a very low “memory” of previous trends. If, for example, Arctic sea ice extent is very low in September, winter heat loss is high, encouraging the formation of more sea ice. Such processes explain high year-to-year fluctuations in sea ice, yet they do not preclude long-term trends.
Model simulations, scientific proxy data, and documentary evidence assessed by interdisciplinary scholars can contextualize sea ice in the modern Arctic in light of the distant past. My own recent research suggests that sea ice extent in the Arctic north of Europe during December 2014 is not dissimilar to what was encountered by European polar explorers during summer expeditions at the height of the Little Ice Age. This reflects climate change on a remarkable scale, given the vast annual difference between summer and winter sea ice coverage in the Far North.
Ultimately, Arctic sea ice fluctuates from year to year in ways that can temporarily mask gradual climate change. The world is warming, and the Arctic is warming faster than anywhere else. It is important to keep an eye on the recent recovery in Arctic sea ice, but all indications are that it is just a momentary reprieve in a very worrisome trend.