Report From Climate.gov
Despite the fact that the area of the Arctic Ocean covered by sea ice during the winter maximum has declined only slightly in recent decades, the ice itself is profoundly different than it used to be. Very old ice—thick, strong, and more melt-resistant—has nearly vanished, and the amount of first-year ice—thin, salty, and unlikely to survive the summer—has skyrocketed.
These satellite-based maps show the age of the ice in the Arctic at the end of winter in March 1985 (left) and March 2017 (right). The first age class on the scale (1, darkest blue) means “first-year ice,” which formed in the most recent winter. The oldest ice (>7, white) is ice that is more than nine winters old. Dark gray areas indicate open water or coastal regions where the spatial resolution of the data is coarser than the land map.
Historically, ocean currents exported old ice out of the Arctic through the Fram Strait, near Greenland. Meanwhile, multi-year ice continued to be built in the Beaufort Gyre, north of Alaska. Ice floes would circulate in that loop for many years, growing thicker and stronger. In many years during recent decades, however, the southern arm of the Beaufort Gyre is too warm for sea ice to survive. Multi-year ice is lost from the Arctic as it always has been, but it is being rebuilt at much slower rates.
As sea ice ages, it adds volume, expels salt, and is toughened up by jostling and collisions. Very old ice may be more than 10 feet thick. These characteristics make it better able to withstand warm weather and pounding from storm waves; its loss makes for a more fragile ice pack. As reported in the 2017 Arctic Report Card, sea ice older than four winters made up 16 percent of the Arctic sea ice pack in March 1985. In March 2017, it made up less than 1 percent. Meanwhile, first-year ice constituted roughly 55 percent of the Arctic sea ice pack in March through the 1980s. In March 2017, first-year ice comprised nearly 80 percent of the ice pack.
This large amount of young ice becomes self-reinforcing: it melts easily in the summer, leaving more open water exposed to sunlight during the Arctic’s long summer days. More solar heating raises ocean temperatures, which further impedes ice growth. This feedback loop is helping to establish the small summer ice extents of the past decade as the new normal for the Arctic.
Maps by NOAA Climate.gov, adapted from Figure 3b in “Sea Ice” chapter of the 2017 Arctic Report Card, based on data provided by Mark Tschudi.
In the 2017 issue of NOAA’s Arctic Report Card, scientists report on a body of paleoclimate research that shows that the extent and rate of sea ice decline in the Arctic is unprecedented over at least the past 1,500 years. Reconstructions such as this one extend our knowledge into the distant past, and they provide context for the extraordinary increases in ocean temperature and decreases in ice extent that have occurred in recent times.
This time series shows the Arctic sea ice extent in millions of square kilometers over the past roughly 1,500 years. Scientists use climate proxies like sediment/ice cores, tree rings, and fossilized shells of ocean creatures to extend the sea ice extent records back in time. 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. And just as importantly, it is beyond the range of natural variability, implying a human component to the drastic decrease observed in the records.
The minimum sea ice extent, which occurs each summer, is influenced by the atmospheric circulation, air temperature, and variations in the amount of warm water that flows into the Arctic. Since 1900, waters that enter the Arctic Ocean through the Fram Strait have increased by 2 degrees Celsius (4 degrees Fahrenheit). Meanwhile, proxy records show that the current warming trend in surface air temperatures has not been observed in the Arctic over at least the last 2,000 years.
Sea ice in the Arctic Ocean has a history much longer than the last 2,000 years. It likely first formed about 47 million years ago. However, perennial—year round—sea ice at the North Pole first occurred 14-18 million years ago. A number of paleoclimate studies have shown that perennial sea ice has existed in the central Arctic for much of the last 350,000 years, with significant regional variability. This variability highlights the importance of expanding the number of paleoclimate reconstructions to better predict which regions are most susceptible to further sea ice loss.
Throughout geologic times, the amount of sea ice increased and decreased along with changes in temperature, atmospheric carbon dioxide concentrations and the ice-age climate cycles. In fact, there were intermittent periods of ice-free conditions in the past 350,000 years up until the “modern” era of sea ice conditions began about 5,000 years ago.
These ice-free periods usually coincided with times when solar energy reaching the Arctic was at its largest due to small variations in the shape of Earth’s orbit and its axis of rotation. However, since the latter half of the Holocene epoch (about 5,000 years ago), some amount of year-round Arctic sea ice cover has been present. But as we move through the rest of the century, some climate model projections suggest that ice-free Arctic summers will return, possibly as early as 2030, but very likely before 2100.
The Arctic plays a vital role in our planet’s climate and can serve as a canary in a coalmine for ongoing impacts from human-caused climate change. Understanding how the Arctic is going to change in the future, including changes in sea ice and impacts on Arctic ecosystems, requires a continued effort to develop additional reconstructions like the one above to help scientists better grasp what makes the Arctic Ocean tick.
Adapted from Figure 3 in “Paleoceanographic Perspectives on Arctic Ocean Change” in the 2017 Arctic Report Card. Original data from Kinnard et al., 2011.