Arctic and global warming

Global warming is being felt most intensely in the Arctic, where ice and snow have been consistently melting away. Arctic Ocean ice cover has shrunk more dramatically in the twenty-first century than at any time since detailed records have been kept.

Background

According to the "Arctic Climate Impact Assessment Scientific Report," produced by 250 scientists under the auspices of the Arctic Council, Arctic sea ice was half as thick in 2003 as it had been thirty years earlier. The melting of ice in the Arctic accelerated through 2007, advancing the projected date of an ice-free summer to perhaps 2027. During September 2007, the Arctic ice cap shrank to what was, at the time, its smallest extent since records have been kept, 4.12 million square kilometers, versus the previous record low of 5.28 million square kilometers in 2005. The shrinkage from 2005 to 2007 represented a loss of more than 20 percent of the Arctic’s ice cover, or an area the size of Texas and California combined.

These trends continued into the 2010s. In August 2012, the sea ice extent had decreased even further than in 2007 to 4.10 million square kilometers, making this record the lowest in satellite history. The US National Oceanic and Atmospheric Administration's (NOAA) 2015 Arctic Report Card found that the maximum extent of sea ice set a new record low in 2015 since record keeping began in 1979. The average air temperature on land in the Arctic that year also set a new record high since 1900. The escalation of global warming in the Arctic paralleled the global pattern (both 2014 and 2015 set average global high temperature records), but the sensitivity of the Arctic environment makes it particularly at risk to major environmental disruption due to climate change.

Following the summer of 2016, scientists were suprised to find that the Arctic ice extent minimum had once again shrunk to a record low of 4.14 million square kilometers, effectively tying the 2007 record for the second-lowest extent since the beginning of the use of satellite analysis. Though the ice had begun to melt at a faster pace subsequent to a record low yearly maximum extent in March, satellites had recorded a more unusual decrease in melting during the summer likely due to atmospheric pressure and cloud cover. Since ice melting usually increases during the months of June and July, scientists were not expecting the sharp receding of the ice back to the low 2007 extent in September. The atypical melting pattern confirmed scientists' conclusions that the loss of older, thicker ice has left the ice more susceptible to changing weather conditions (including storms, such as the two cyclones that passed over the Arctic Ocean in August) later in the season than in the past.

Retreat of Arctic Ocean Ice

Scientists were shaken by the sudden retreat of the Arctic ice during the summer of 2007, which was much greater than their models had projected. Some said that a tipping point had been reached and that the Arctic could experience ice-free summers within a decade or two. At the annual American Geophysical Union meeting in San Francisco during December 2007, scientists reported that temperatures in waters near Alaska and Russia were as much as 5° Celsius above average.

Scientists at the University of Washington said the sun’s heat made the greatest contribution to the record melting of the Arctic ice cap at the end of summer in 2007. Sunlight added twice as much heat to the water as was typical before 2000. Relatively warm water entering the Arctic Ocean from the Atlantic and the Pacific Oceans was also a factor, according to Michael Steele, an oceanographer at the University of Washington. Energy from the warmer water delayed the expansion of ice in the winter as it warmed the air.

In addition to the retreating extent of sea ice in the Arctic, a greater proportion of the ice that does remain in the region is thin and freshly formed, unlike older, thicker ice that is more likely to survive future summer melting. The proportion of older, “durable” ice dropped drastically between 1987 and 2007, according to studies by Ignatius G. Rigor of the University of Washington. In addition to a decrease in the extent of Arctic Ocean ice, by 2007 large areas of the ice that remained were only about one meter thick—half what they had been in 2001, according to measurements taken by an international team of scientists aboard the research ship Polarstern. In 2015 NOAA reported that the amount of first-year new ice in February and March was double that of thirty years prior, reflecting the extreme loss of older ice. This trend continued into the 2020s. In the 2020 Arctic Report Card, experts recorded the decline in sea ice: 2.54 million square miles (6.85 million square kilometers) from 1979 to 1992; 2.37 million square miles (6.13 million square kilometers) from 1993 to 2006; and 1.71 million square miles (4.44 million square kilometers) from 2007 to 2020. According to NASA, by 2024, the ice had shrunk to a low of 1.31 million square miles (3.39 million square kilometers). This was about 750,000 square miles (1.94 million square kilometers) below the end-of-summer average of 2.4 million square miles (6.22 square kilometers) from 1981 to 2010.

Walrus Deaths

With ice receding hundreds of kilometers offshore during the late summer of 2007, walruses gathered by the thousands on the shores of Alaska and Siberia. According to Joel Garlich-Miller, a walrus expert with the US Fish and Wildlife Service, walruses began to gather onshore late in July, a month earlier than usual. A month later, their numbers had reached record levels from Barrow to Cape Lisburne, about 480 kilometers southwest, on the Chukchi Sea. Walruses dive from the ice to feed on clams, snails, and other bottom-dwelling creatures. As a result of increased melting, however, the Arctic ice has receded too far from shore to allow walruses to engage in their usual feeding patterns.

A walrus can dive 180 meters, but water under receding ice shelves is now more than a thousand meters deep by late summer. The walruses have been forced to swim much farther to find food, using energy that could cause increased calf mortality. In addition, more calves are being orphaned. Russian research observers have reported many more walruses than usual on shore, tens of thousands in some areas along the Siberian coast. These creatures would have stayed on the sea ice in earlier times.

Walruses are prone to stampedes when they gather in large groups. The appearance of a polar bear or a human hunter, or even noise from a low-flying small airplane, can send thousands of panicked walruses rushing to the water, stampeding one another into bloody pulp. Thousands of Pacific walruses were killed on the Russian side of the Bering Strait during the late summer of 2007, when more than forty thousand hauled out on land at Point Shmidt as ice retreated northward. Scientists reported in 2015 that the continued loss of walrus habitat is further complicated by secondary effects of global warming, such as greater development and shipping in the Arctic (including for gas and oil projects), acidification of the ocean, and the spread of disease and contaminants.

Forecasts

In the past, low-ice years often were followed by recovery the next year, when cold winters or cool summers kept ice from melting further. That kind of balancing cycle stopped after 2002. The year 2004 was the third in a row with extreme ice losses, indicating acceleration of the melting trend. Arctic ice has been declining by about 8 percent per decade as part of this trend.

Beginning in 2005, scientific projections for the Arctic were becoming more severe. A climate modeling study published in the Journal of Climate indicated that if humanity does not address global warming in the near future, irreversible damage may take place. The paper’s lead author, Govindasamy Bala of the US Energy Department’s Lawrence Livermore National Laboratory, predicted that it might take twenty or thirty years before the scope of anthropogenic climate change becomes evident, but that after that the damage would be obvious.

The Journal of Climate study projected that the global concentration of atmospheric carbon dioxide (CO₂) would be double that of preindustrial levels in 2070, triple in 2120, and quadruple in 2160—predicting slightly less than present-day rates of increase. It was the first study to assume consumption of all known reserves of fossil fuels. This model anticipates that the Arctic will see the planet’s most intense relative warming, with average annual temperatures in many parts of Arctic Russia and northern North America rising by more than 14° Celsius by about 2100.

Acceleration of Ice-Cap Melting

Julienne Stroeve and her colleagues compared more than a dozen models of Arctic ice-melt and found that nearly all of them underestimated the actual speed of ice-melt, in many cases by large amounts. These findings have two important implications, according to a summary of Stroeve’s study in Science. First, the effect of increasing greenhouse gases may have been greater than has been believed. Second, future loss of Arctic Ocean ice may be more rapid and extensive than predicted. Within a decade, projections of the first ice-free summer in the Arctic had moved from the end of the twenty-first century to roughly the year 2027.

Beginning in the mid-1990s, scientists observed pulses of relatively warm water from the North Atlantic entering the Arctic Ocean, further speeding ice-melt. Mark Serreze, senior research scientist at the National Snow and Ice Data Center, said that such warm-water pulses represented yet another potential kick to the system that could accelerate rapid sea-ice decline and send the Arctic into a new state. As Arctic ice retreats, ocean water transports more heat to the Arctic, and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice.

The entire Arctic system is thus beset by accelerating feedback loops that intensify climate change. For example, permafrost has been melting, injecting additional CO₂ and methane into the atmosphere. In Alaska, trees that have become destabilized in melting permafrost lean at angles, creating so-called drunken forests.

The speed of ice breakup can sometimes be astonishing. For example, the thirty-meter-thick Ayles shelf of floating ice, a shelf roughly sixty-five square kilometers in area, had extended into the Arctic Ocean from the north coast of Ellesmere Island in the Canadian Arctic for roughly three thousand years. The Ayles shelf was detached during the summer of 2005 by wind and waves in warming water. The break-up was observed by Laurie Weir of the Canadian Ice Service in satellite images of Ellesmere Island during August 2005. The images showed a broad crack opening and the ice shelf collapsing and flowing out to sea with a speed that could be observed hour by hour.

In 1906, Arctic explorer Robert Edwin Peary surveyed 26,160 square kilometers of ice shelves. Nine-tenths of these have broken up over the last century, according to Luke Copland, director of the Laboratory for Cryospheric Research at the University of Ottawa.

Context

The extent of Arctic Ocean ice has been declining year-round for more than three decades, according to an analysis of satellite data compiled during 2006 by the US National Ice Center. Data sets of the Thirty-Year Arctic Sea Ice Climatology show shrinkage in the Arctic Ocean summer ice cover of more than 8 percent per decade, according to Pablo Clemente-Colón, the ice center’s chief scientist. While the extent of winter sea ice has also been decreasing, summer shrinkage has become more pronounced.

A tipping point toward an ice-free Arctic in summer probably already has been passed, according to James E. Hansen, former director of the National Aeronautics and Space Administration’s (NASA) Goddard Institute for Space Studies. The complete loss may occur rapidly, on the time scale of a decade, once ice loss has reached such a degree that the albedo feedback becomes a dominant process, according to Hansen. The albedo feedback refers to the fact that loss of some sea ice increases the amount of solar energy absorbed by the Arctic because the liquid ocean is darker than the ice, absorbing more of the Sun’s heat and thus increasing ice melt. Hansen and his team could not determine the exact level of added CO₂ necessary to cause complete ice loss, but they declared that once such a state were reached, it would be difficult to return to a climate with summer sea ice, because of the long lifetime of atmospheric CO₂.

Key Concepts

• albedo: proportion of incident radiation reflected by Earth’s surface
• drunken forest: forest that leans at an odd angle as a result of melting permafrost
• feedback loops: climatic influences that compound or retard each other, accelerating or decelerating the rate of global warming
• permafrost thawing: defrosting of previously permanently frozen ground, usually in or near the Arctic
• tipping point: the point at which feedback loops take control and propel climate change

Bibliography

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