Climate Change: Arctic sea ice summer minimum

September 26, 2019

In the Arctic Ocean, the area covered by sea ice grows and shrinks over the course of the year. Each fall, as less sunlight reaches the Arctic and air temperatures begin to drop, additional sea ice forms. The total area covered by ice increases through the winter, usually reaching its maximum extent in early March. Once spring arrives with more sunlight and higher temperatures, the ice begins to melt back, shrinking to its minimum extent each September.

Through 2018, the downward trend for the summer minimum in September was 12.8 percent per decade relative to the 1981–2010 average. (The trend is updated each year as part of NOAA's Arctic Report Card, which is released in mid-December.) Summer ice declines have been especially rapid since the start of the twenty-first century.

Explore this interactive graph: Click and drag to display different parts of the graph. To squeeze or stretch the graph in either direction, hold your Shift key down, then click and drag. This graph shows the average area covered by sea ice during September each year. Minimum sea ice extent has decreased 12% per decade since 1979. Data provided by the National Snow and Ice Data Center.

Just as ponds and lakes in northern states develop a layer of ice on their surfaces during cold winters, the surface of the Arctic Ocean also freezes, forming sea ice. Seawater has a lower freezing point than fresh water, but once it is chilled to around -2°C (about 28°F), the salty liquid begins to solidify. Ice crystals appear on the sea's surface, and if the air is cold enough, the crystals expand to form a slushy mix, then a solid covering of ice that can thicken over time.

Early observations of sea ice coverage in the Arctic come to us both from the oral histories of native populations and from the records of early European mariners who were seeking a "Northwest Passage" to the lucrative markets in Asia. For as long as humans have been keeping track, large areas of the Arctic Ocean have remained covered by sea ice throughout the year.

A map in polar projection of Arctic sea ice concentration on September 18 2018, and a graph of daily ice concentration throughout the satellite record

(top) Sea ice concentration (light blue to white) on September 18, 2019, the day of the summer minimum extent. The gold line is the median extent for 1981-2010: half of years had smaller extents, half had larger. (bottom) A graph of daily ice extent each year of the satellite record. Earlier years are in shades of light blue; recent years are in dark blue. The 2019 daily extent line is in dark pink. NOAA Climate.gov image, based on data from the National Snow and Ice Data Center.

However, over the past 40 years, the area covered by ice has shown a dramatic decrease. Since satellite-based measurements began in the late 1970s, data show a trend of more ice melting away during summers and less new ice forming during winters. On September 18, 2019, the sea ice cover reached its annual summer minimum, tying with 2007 and 2016 for second-smallest on record: the area of the Arctic Ocean where sea ice concentration was at least 15 percent sea ice was 1.60 million square miles (4.15 million square kilometers). 

In the early twentieth century, explorer Roald Amundsen took three years (1903–1906) to traverse the Northwest Passage. Since the turn of the twenty-first century, that passage has experienced relatively ice-free conditions multiple times, though it's not yet a dependable pathway for commercial ships. The Northern Sea Route along the coast of Siberia has begun experiencing summertime sea ice declines that may transform it into a reliable shipping route. The opening of shipping lanes across the Arctic may provide shippers with viable alternatives to traveling through the Panama Canal or around the southern tip of South America. This new reality will have impacts not only on the environment, but also on the world economy and national security, as nations compete to gain rights to shipping lanes and newly accessible resources in the Arctic.

Climate scientists are particularly concerned about the decrease of sea ice because its white surface reflects up to 80 percent of incoming sunlight, deflecting additional energy away from the planet. With less ice present, the dark surface of ocean water absorbs considerably more sunlight energy, leading to further warming of the atmosphere and more melting of ice, which leads to further warming... Scientists are actively studying the effects of this positive feedback loop to help them understand and predict how the observed decrease in Arctic sea ice will affect the global climate system.

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Popular Arctic sea ice visualizations

Polar map showing Arctic sea ice concentration at the winter maximum in March 2018

Sea ice concentration on March 17, 2019—the maximum extent of the year—compared to the median winter maximums between 1981-2010 (gold line). Full story

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Pair of maps showing Arctic sea ice age at the winter maximum in 1985 (left) versus 2018 (right)

These maps show the age of sea ice in the Arctic winter maximum ice pack in March 1985 (left) and March 2018 (right). Less than 1% of ice is 4 or more years old. Full story

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1 minute, 20 seconds

 This animation tracks the relative amount of ice of different ages from 1990 through early November 2016. Seasonal ice is darkest blue. Ice that is 9 or more years old is white. Video produced by the Climate.gov team, based on NOAA and NASA data provided by Mark Tschudi, University of Colorado-Boulder. Data processing by Hunter Allen. Editing by Bruce Sales. Narration by Deke Arndt, NCEI. 

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Previous years' minimums

2018 Arctic sea ice minimum

Arctic sea ice concentration on September 19, 2018, one of the two dates that sea ice experienced its minimum extent in 2018. Higher concentration appears white, and lower concentration appears blue. Extent is the area covered by at least 15% sea ice, and the yellow line indicates the 1981–2010 median extent for this date. Image adapted from NASA Earth Observatory using data from the National Snow and Ice Data Center.

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Monthly sea ice concentration in the Arctic during the 2017 summer melt season from April–August, ending with the daily concentration on September 13, the preliminary date of the annual minimum extent. Animation by NOAA Environmental Visualization Lab, based on data from the National Snow and Ice Data Center. Full story

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Arctic sea ice minimum as of September 10, 2016

Arctic sea ice concentration on the date of the 2016 minimum extent, September 10, 2016. NOAA Climate.gov image based on NOAA and NASA satellite data from NSIDC. Full story

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Arctic sea ice map

Map of Arctic sea ice on September 11, 2015, the date it reached its fourth-lowest extent in the satellite record. Full story

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Map of Arctic sea ice concentration in September 2014 in shades from light blue to white

Sea ice concentration on September 17, 2014. Areas where the surface was less than 15% ice covered are deep blue; places that were 100% ice covered are solid white. The orange line shows the 1981-2010 median extent for September 17. Full story 

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Sea ice concentration in September 2013 compared to the median extent from 1981-2010 (gold line) and the 2012 record low (gray line).  Map by NOAA Climate.gov, based on data provided by the National Snow and Ice Data Center. Adapted from Figure 5.12(b) in State of the Climate in 2013. Full story

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Map shows ice concentration on September 16, 2012—the smallest summer minimum on record—along with the extent of the previous record low, in 2007 (yellow line), and the mid-September median extent from 1981-2010 (black line). Full story

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A graph of Arctic sea ice extent from 500 AD to the present, overlaid on a photo of sea ice

Arctic sea ice extent in millions of square kilometers over the past roughly 1,500 years. These records show that while there have been several periods over the past 1,450 years when sea ice extents expanded and contracted, the decrease during the modern era is unrivaled. Full story

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Map of Bering Strait and Chukchi Sea showing percent ice cover

Sea ice extent (percent ice cover) on November 19, 2017, mapped by a combination of satellites (synthetic aperture radar and passive microwave sensors) and ground-based radar. Except for a few areas of nearshore ice, the entire Bering Sea is ice-free as are thousands of square miles of the Chukchi Sea to the north. Full story

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Further Reading

Arctic Meltdown, Economic and Security Implications of Global Warming. Foreign Affairs, Scott G. Borgerson. Accessed March 17, 2009.

References

All About Sea Ice, National Snow and Ice Data Center. Accessed March 17, 2009.

State of the Cryosphere: Sea Ice, National Snow and Ice Data Center. Accessed January 11, 2017.

Arctic Sea Ice News and Analysis, National Snow and Ice Data Center. Accessed September 26, 2019.

Intergovernmental Panel on Climate Change. (2013). Climate Change 2013: The Physical Science Basis Summary for Policymakers. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Data

September Sea Ice Extent, National Snow and Ice Data Center.

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