Mark C. Serreze: Approaching the March Sea Ice Maximum

Author Mark C. Serreze standing next to a snow machine in the Arctic.

The floating sea ice atop the Arctic Ocean waxes and wanes with the seasons. The maximum extent typically occurs around the second week of March, at which time ice has historically covered an area a bit less than twice the size of the contiguous United States. The term “Arctic sea ice extent” is actually a bit of a misnomer, for at or near the seasonal maximum, sea ice is found well south of the Arctic Circle, covering all of Hudson Bay and parts of the Bering Sea, the Sea of Okhotsk, the Baltic Sea and the Gulf of St. Lawrence.  With the start of spring, the ice cover begins to melt.  Initially, the growing warmth of spring slowly nibbles away at the southern edges of the ice pack.  The pace of melt picks up in May and June, and then gets underway in earnest in July.  As the sun gets lower in the sky in August, the melt slows.  The seasonal minimum in ice extent usually occurs in mid-September – at that time, the ice covers less than half of what it did in March, and ice is restricted to the Arctic Ocean proper.  As the sun then sets over the Arctic Ocean, the ice cover begins to grow again, renewing the cycle that has been going on for millions of years. 

But things are changing fast.  Earth observation satellites have been recording changes in Arctic sea ice extent since 1979.  These records show that sea ice extent is declining in all months, with the largest change in September, at the end of the melt season.  The downward trend for September is a whopping 13% per decade. The trends are by no means smooth – there are big ups and downs from month to month and year to year, but the pattern is clear. 

Scientists have long been at work to determine what sea ice conditions were like before the satellite era.  Data from shore observations, ship and aircraft reports, and before aviation, sources like logbook entries from whaling ships, extend the record back to 1850.  Paleoclimate reconstructions bring the record back a thousand years before today.  There is no evidence in any of these records for sea ice trends like we’ve seen over the past 40 years.  They are unprecedented.  The conclusion is inescapable – the Arctic Ocean is quickly losing its floating sea ice cover.  The summer ice cover may be gone 30 or 40 years from now.

At the University of Colorado National Snow and Ice Center (NSIDC), where I’ve been the director since 2009, we track the Arctic sea ice cover on a daily basis.  Every August, we start to brace ourselves for the inevitable tidal wave of questions from the media and interested public about what September will bring.  Questions like: Will there be a new record low in sea ice extent this year?  When will the Arctic completely lose its summer sea ice cover?  What will this mean for the rest of the planet?  We also get our share of flak from the skeptics, eager to tell us that this is all some sort of natural climate cycle, or that nothing is happening at all; we’re making it up and fudging the records.  We shrug this off and diligently continue processing the satellite data and report on what is happening. The data does not lie.

Until a few years ago, the March sea ice maximum went relatively unnoticed.  By comparison to September, the changes being seen in winter weren’t especially spectacular, and for good reason – even in a warming Arctic, it still gets cold and dark in winter and sea ice forms and covers a big area.  The ice that grows in autumn and winter is thinner than it used to be, but to the satellite sensors that we use to determine ice extent, thin ice looks pretty much the same as thick ice.

Things changed in 2015, when sea ice extent at the March maximum set a new record low.  Then the winter of 2015-2016 saw a mind-boggling heat wave over the Arctic Ocean.   At the end of December 2015, there was a brief period when the surface temperature at the North Pole rose to the melting point. In all my years of studying the Arctic, I’d never seen anything like it. It stayed warm and on March 24, when Arctic sea ice reached its seasonal maximum extent, it had bested the low mark set in 2015.  The winter of 2016/2017 was in many respects a repeat.   At the winter solstice on Dec. 22, temperatures near the North Pole were up 20 degrees Celsius (35 degrees Fahrenheit) above average.  When March 2017 rolled around, another new record low in extent had been set. The Arctic has gone crazy.

We’re still coming to grips with understanding these records lows in the winter ice cover. While the heat waves are clearly related to weather patterns bringing in warm air from the south, what’s the cause of these patterns?  While more ocean heat seems to be coming into the Arctic Ocean from the Pacific through the Bering Strait, why is this happening?  The inflow of ocean heat from the Atlantic has also changed in puzzling ways that inhibit winter ice formation in places like the Barents Sea.  

In short, while we know a great deal about what is happening to the Arctic and where it is headed, the emerging Brave New Arctic continues to challenge us.  Maybe we shouldn’t be all that surprised – after all, scientists have long known that, as the climate warms, the biggest changes would be seen the Arctic. That doesn’t mean that we can’t be amazed.


Mark C. Serreze is is director of the National Snow and Ice Data Center, professor of geography, and a fellow of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. He lives in Boulder, Colorado.