Speaking at the annual meeting of the American Geophysical Union in San Francisco in December 2007, Richard Alley of Pennsylvania State University surveyed the major—and accelerating—effects that a relatively small amount of warming (compared to what is anticipated for the rest of the century) has already had on the melting of ice in the Arctic and Antarctic. “If a very small warming makes such a difference,” asked Alley, “it raises the question of what happens when more warming occurs.” At the same meeting, Josefino Comiso of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said, “The tipping point for perennial sea ice has likely already been reached” ( Kerr 2008 ). “When the ice thins to a vulnerable state, the bottom will drop out and we may quickly move into a new, seasonally ice-free state of the Arctic,” said glaciologist Mark Serreze. “I think there is some evidence that we may have reached that tipping point, and the impacts will not be confined to the Arctic region” ( “As Arctic Sea Ice” 2008 ).

Shrinking sea ice in the Arctic reinforces conditions that provoke further warming, one important example of positive climatic feedbacks that make global warming dangerous in the long term. This process is called polar amplification and was described thusly by James A. Scree and Ian Simmonds:

Over several decades, the extent of snow cover in the Arctic has changed significantly and has had consequent impacts on climate. As snow covers the land surface for less time, reflectivity (albedo) changes, allowing less reflection and more absorption of solar radiation at the surface. Between 1979 (when satellite mapping began) and 2012, the extent of snow cover at high latitudes has been Page 225  |  Top of Articledeclining an average of 17.6 percent per decade. Because of this, “The snow-cover study authors … found an overall decline in snow cover from 1967 through 2012, and also detected an acceleration of snow loss after the year 2003. Between June 2008 and June 2012, North America experienced three record-low snow cover extents. In Eurasia, each successive June from 2008 to 2012 set a new record for the lowest snow cover extent yet recorded for that month” ( Derksen and Brown 2012 ; “Snow Cover” 2013 ).

The British scientific journal Nature reported in 2014 that snow thickness had decreased by around 37 percent in the western Arctic and by 56 percent in the Beaufort area, comparing observations from 1954 to 1991 from Soviet ice stations with radar surveys (2009–2013) by satellite that had been partially verified by reports from the surface by Melinda Webster of the University of Washington and her colleagues ( “Arctic Snowpack” 2014 ).

Other research has identified a link between rising air temperatures and shrinking snow cover, according to NASA’s Earth Observatory ( “Snow Cover” 2013 ). The Earth Observatory’s report continued: “Snow has very high albedo, reflecting up to 90 percent of the sunlight it receives. As snow cover declines, dark soils and vegetation absorb more of the sun’s energy.… The uppermost layer of permafrost that thaws each summer. When organic material in thawing permafrost decomposes, it can release methane, a potent greenhouse gas when released to the atmosphere.”

During November 2010, extreme warmth in northeastern Canada was related to an ice-free Hudson Bay, which is unusual. The contrast of temperatures at coastal stations in years with and without sea ice cover on the neighboring water body is useful for illustrating the dramatic effect of sea ice on surface air temperature. Sea ice insulates the atmosphere from ocean water warmth, allowing surface air to achieve temperatures much lower than that of the ocean. It is for this reason that some of the largest positive temperature temperatures on the planet have occurred in the Arctic because sea ice area has decreased in recent years ( Hansen et al. 2010 ).

Weather patterns can influence the way in which Arctic ice melts and reforms, providing variations from year to year that obscure long-term trends. For example, weather patterns (especially a severe cyclonic storm in August 2012, the most intense August storm to hit the region since satellite monitoring began in 1979) helped to destroy ice, whereas the patterns of 2013 inhibited ice breakup. The vast difference between the two melt seasons had researchers investigating the ways in which cyclones can either exacerbate or dampen the effects of climate warming on sea ice.

“As global warming continues and cyclones become more intense, many researchers worry that summers like that of 2012 could become the norm,” Lauren Morello wrote in Nature (2013) . In the 2012 cyclone, “wind and wave action driven by the tempest caused a massive chunk of ice … to separate from the main pack.… The sheared-off portion eventually melted, depleting the overall ice cover and leaving the main pack more vulnerable to erosion from wind, waves, and warm water stirred up by the storm” ( Morello 2013 ). The area of disturbed ice has been variously estimated at between 150,000 and 400,000 square kilometers. In 2013, Page 226  |  Top of Articlecyclones brought in cold air and aided ice formation, blocking sunshine late in the melt season. “Yet scientists say that future summer storms are more likely to accelerate ice loss than to slow it, as rising temperatures continue to deplete the Arctic’s ice cover.” Morello continued. “Thick, ‘multiyear’ ice that has survived more than one summer thaw once covered large expanses of the Arctic Ocean. Now those waters are dominated by thin, ‘first-year’ ice—which forms in autumn and melts the next summer, and is more vulnerable to the fierce winds and waves that the cyclones bring.”

In the past, low ice years often were followed by recovery the next year when cold winters favored accumulation or cool summers kept ice from melting. That kind of balancing cycle stopped after 2002. “If you look at these last few years, the loss of ice we’ve seen, well, the decline is rather remarkable,” said Mark Serreze ( Human 2004 ).

A NASA analysis of satellite data for the first time in 2010 measured the pace at which stronger, older “multiyear” ice is melting in the Arctic Ocean and being replaced by thinner, more fragile ice that usually melts each year. Some scientists suspected that losses in ice coverage over the Arctic Ocean have been mainly from wind pushing the ice, movement that scientists call “export.” In this study, Ron Kwok and Glenn Cunningham at NASA’s Jet Propulsion Laboratory in Pasadena, California, used satellite data to show the role of export versus actual melting. within the Arctic Ocean basin. Kwok and Cunningham showed that from 1993 to 2009, 1,400 cubic kilometers (336 cubic miles) of ice was lost because of melt, not export. “The paper shows that there is indeed melt of old ice within the Arctic basin and the melt area has been increasing over the past several years,” Kwok said. “The story is always more complicated—there is melt as well as export—but this is another step in calculating the mass and area balance of the Arctic ice cover” ( “NASA Study” 2010 ).

One study found that “multiyear” ice, which had been assumed to be more durable than the thinner single-year ice that forms after melting, may be at least as vulnerable. NASA scientist Josefino C. Comiso found that “Arctic multiyear ice ‘extent’—which includes all areas where at least 15 percent of the ocean surface is covered by multiyear ice—has been vanishing at a rate of about 15.1 percent per decade.… Over the same period, the ‘area’ covered by multiyear ice—which discards open water among ice floes and focuses exclusively on regions that are completely covered—has been shrinking by about 17.2 percent per decade” ( Comiso 2012 ; “Oldest Arctic” 2012 ).

“The Arctic sea ice cover is getting thinner because it’s rapidly losing its thick component,” Comiso said. “At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season. It would take a persistent cold spell for multiyear sea ice to grow thick enough again to be able to survive the summer melt season and reverse the trend” ( Comiso 2012 ). “We’re seeing more melting of multiyear ice in the summer,” said Julienne Stroeve, senior research scientist with the National Snow and Ice Data Center in Boulder, Colorado. “We may Page 227  |  Top of Articlesoon reach a threshold beyond which the sea ice can no longer recover.” “We have already witnessed major losses in sea ice, but our research suggests that the decrease over the next few decades could be far more dramatic than anything that has happened so far,” said Marika Holland of the National Center for Atmospheric Research, also in Boulder. “These changes are surprisingly rapid” ( “As Arctic Sea Ice” 2008 ).

“It’s hard even for people like me to believe, to see that climate change is actually doing what our worst fears dictated,” said Jennifer A. Francis, a Rutgers University scientist who studies the effect of sea ice on weather patterns. “It’s starting to give me chills, to tell you the truth” ( Gillis and Foster 2012 ).

Robert F. Spielhagen and colleagues wrote in Science early in 2011 that relatively warm water flowing from the Atlantic Ocean into the Arctic is strongly affecting the coverage and distribution of ice. “Early 21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2,000 years and are presumably linked to the Arctic amplification of global warming,” they wrote. “Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only about 150 years” ( Spielhagen et al. 2011 , 450).

How well do observations and models agree on Arctic ice melt? Julienne Stroeve and colleagues compared more than a dozen models and found that nearly all of them underestimated the speed of ice melt—in many cases by large amounts. “These findings have two important implications,” said a summary of this study in Science. “First, that the effect of rising greenhouse gases may have been more important than has been believed; and second, that future loss of Arctic sea ice may be more rapid and extensive than predicted” ( “Melting Faster” 2007 ). “Climate models have predicted a retreat of the Arctic sea ice; but the actual retreat has proven to be much more rapid than the predictions,” said Claire Parkinson, a climate researcher at NASA Goddard. “There continues to be considerable interannual variability in the sea ice cover, but the long-term retreat is quite apparent” ( “Visualizing” 2012 ).

In addition to sea ice, land ice in the northern and southern Canadian Arctic archipelago declined sharply between 2004 and 2009, according to a study in Nature as reported by a team led by Alex Gardner of the University of Michigan. In six years (2004–2009), the islands lost an average of 61 gigatons (61 billion tons of ice) per year. The scientists also found that the rate of loss is accelerating. From 2004 to 2006, the average mass loss was roughly 31 gigatons per year; from 2007 to 2009, the loss increased to 92 gigatons per year ( “Ice Loss” 2011 ).

Sea ice across the Arctic Ocean has been melting much more quickly than earlier anticipated even by the most recent computer models. Latest projections indicate that the Arctic Ocean may be without summer ice by 2020. Even projections made by the Intergovernmental Panel on Climate Change (IPCC) in its 2007 assessments (forecasting an ice-free Arctic summer between 2050 and 2100) were out of date weeks after they were made public, according to reports by scientists at the National Center for Atmospheric Research and the University of Colorado’s National Page 228  |  Top of ArticleSnow and Ice Data Center. The study, “Arctic Sea Ice Decline: Faster Than Forecast?” was published in May 2007 in the online edition of Geophysical Research Letters. This study was led by Julienne Stroeve of the National Snow and Ice Data Center and funded by the National Science Foundation and NASA.

In a separate study released in March 2006, Stroeve and her team showed that dwindling Arctic sea ice may have reached “a tipping point that could trigger a cascade of climate change reaching into Earth’s temperate regions” ( “Arctic Ice Retreating” 2007 ). “This suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC projections,” said Stroeve ( “Arctic Ice Retreating” 2007 ).

The pronounced thinning of Arctic sea ice has made the ice pack more brittle and susceptible to wind drift. The volume of Arctic sea ice decreased by one-third during 2007–2011 compared with the 1979–2006 mean. As Richard Kerr wrote in Science (2012) , “Thinning of Arctic sea ice has made it more brittle, and more likely to break up because of wind drift, according to a model simulation by Jinlun Zhang at the University of Washington in Seattle and his colleagues” ( “Thinning Ice” 2012 ). “The volume of Arctic sea ice decreased by one-third during 2007–2011 compared with the 1979–2006 mean.”

Scientists were surprised by the sudden retreat of the Arctic sea ice during the summer of 2007, which was much more extensive than their models had anticipated. “The Arctic is often cited as the canary in the coal mine for climate warming,” said Jay Zwally, a climate expert at NASA. “Now as a sign of climate warming, the canary has died” ( Kolbert 2007 , 44). “We could very well be in that quick slide downward in terms of passing a tipping point,” said Mark Serreze, a senior scientist at the National Snow and Ice Data Center, in Boulder, Colorado. “It’s tipping now. We’re seeing it happen now” ( “As Arctic Sea Ice” 2008 ). Bob Corell, who headed a multinational Arctic assessment, said, “We’re moving beyond a point of no return” “As Arctic Sea Ice” 2008).

By 2007, Baffin Island in the Canadian Arctic had lost half its ice in 50 years as glaciers on its northern mountain ranges eroded. In another 50 years, what remains may be gone, according to research by geological sciences Professor Gifford Miller of the University of Colorado–Boulder’s Institute of Arctic and Alpine Research and colleagues ( “Baffin Island” 2008 ). “Even with no additional warming, our study indicates these ice caps will be gone in 50 years or less,” he said ( Anderson et al. 2008 ). Many observations combined with some climatic perspective present scientists with an alarming forecast of global ice-melting patterns to come. Bear in mind that because of thermal inertia ice that is melting now in the Arctic, Antarctic, and mountain ranges of the Earth reflects greenhouse-gas emissions of roughly 50 years ago—that is, in this instance, the mid-to-late 20th century. Add the fact, explained elsewhere in this work, that ice melts much more quickly than it forms. Combine that with knowledge that oceans rise not only from actual rise of water but also from expansion of its volume with warmth. The geophysical facts present an alarming warning of accelerating rises in sea levels in the coming century and beyond. Taking a world-wide perspective, combining it with historical perspective Page 229  |  Top of Articleand an understanding of climate science illustrates why scientists who understand all of this have been sounding alarms.

Five years after the record melt of 2007, another massive decline in 2012 again forced scientists to question their models. The director of the National Snow and Ice Data Center (NSIDC), Mark Serreze, said that what remained of the Arctic ice pack was thinner and frailer than before made up of first-year ice. “We have entered a new regime,” he said. “The sea ice is in such poor health in spring that large parts of it can’t survive the summer melt season, even without boosts from extreme weather” ( Schiermeier 2012 , 185)

As Quirin Schiermeier wrote in Nature (2012) ,

Changes in upper-air circulation patterns over the Arctic have created long-lasting weather patterns that have been locked into place by atmospheric blocking across large parts of the Northern Hemisphere. Research into this phenomenon has increased because of their effects on the lives of people in the midlatitudes, said Bob Henson, a meteorologist and acting spokesperson for the University Corporation for Atmospheric Research in Boulder, Colorado. By the time the blocks ease, they can leave behind a “stack of broken records,” he said ( Gaarder 2013 ).

These patterns can shift at a given location, given shifting positions of the block, as Nancy Gaarder of the Omaha World-Herald wrote in 2013 in describing extremes in the upper Midwest:

Writing in Geophysical Research Letters, Jennifer Francis, an atmospheric scientist based at Rutgers University, and atmospheric scientist Stephen Varvus of the University of Wisconsin–Madison have proposed a theory that associates rising temperatures in the Arctic with changes in weather conditions (and the persistence of particular patterns) at lower latitudes.

As Francis and Vavrus wrote,

“The Arctic is warming at two to three times the rate of the rest of the globe,” Francis said.

As Nancy Gaarder also wrote,

Jennifer Francis proposed her theory in 2011—just before record melting of sea ice shocked scientists in 2012. Within three years, she had become a major subject of controversy, as Eli Kintisch reported in Science: “The idea has drawn extensive attention from the media, the public, and influential policy makers, such as White House science adviser John Holdren. Many researchers, however, are skeptical, and some have been vociferously critical. But Francis, whose life and work has been shaped by two round-the-world sailing adventures, has remained calm throughout the storm” ( Kintisch 2014 , 250).

“The question really is not whether the loss of the sea ice can be affecting the atmospheric circulation on a large scale,” said Francis. “The question is, how can it not be, and what are the mechanisms?” ( Gillis and Foster 2012 ). At its basis, Francis theorizes that a warming Arctic and melting sea ice changes the behavior of the jet stream, a high-atmosphere river of air that steers storms and air masses, generally from west to east—except when it slows down and moves north and south as well. These kinks in the upper-level airflow can have major impacts on weather in any given location, serving up heat or cold, drought or deluge. “This means that whatever weather you have today—be it wet, hot, dry, or snowy—is more likely to last longer than it used to,” said Francis. “If conditions hang around long enough, the chances increase for an extreme heat wave, drought or cold spell to occur,” she said, but the weather can change rapidly once the kink in the jet stream moves along ( Gillis and Foster 2012 ).

With his colleagues, climate scientist Ralf Jaiser at the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany, wrote in Tellus (2012), a meteorological journal published in Stockholm, “Our analysis suggests that Arctic sea ice concentration changes exert a remote impact on the large-scale atmospheric Page 231  |  Top of Articlecirculation during winter, exhibiting a barotropic structure with similar patterns of pressure anomalies at the surface and in the midtroposphere. These are connected to pronounced planetary wave train changes notably over the North Pacific.”

Mounting evidence indicates that changes in the Arctic play a role in driving extreme weather at lower latitudes by altering the jet stream. This alteration has made for summer heat waves in North America, Europe, and Asia.

As tundra and permafrost thaw, they release stored carbon dioxide and methane that further raise the atmosphere’s level of greenhouse gases. During Alaska’s unusually warm, dry winter of 2000–2001, the snowless tundra caught fire along Norton Sound, a possible precursor of larger, smoldering fires that could further accelerate global warming. There exists a palatable fear among climate scientists that such feedbacks in the oceans and on land could release large amounts of carbon dioxide and methane currently stored in frozen earth.

In 2009, scientists reported that lightning strikes in the Arctic had increased to 20 times their levels earlier in the 20th century, igniting tundra fires that added more “natural” carbon dioxide to the atmosphere ( Jarvis 2009 , n.p.). Additional evidence that Earth’s frozen regions are already releasing additional greenhouse gases into the air has been provided by M. L. Goulden, et al., who studied boreal forests, finding “ clear evidence that carbon dioxide locked into permafrost several hundred to 7,000 years ago is now being given off to the atmosphere as warming climate melts the permafrost” ( Davis 2001 , 270). The same is true in many cases for methane. According to Neil Davis, author of Permafrost: A Guide to Frozen Ground in Transition (2001) , this “relict” carbon dioxide

Temperatures are now warmer in the Arctic than at any point in the last 2,000 years and at a time when Earth is receiving less heat from the sun because of changes in its orbit. The difference, suggest Darrell S. Kaufman and colleagues in Science in 2009 is greenhouse gas emissions from human activity. A cooling trend during the late 19th century “was caused by the steady orbitally driven reduction in summer insolation.… [It] was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000” ( Kaufman et al. 2009 , 1236). This study also provides fresh evidence for indications that human-generated warming could interrupt the natural ice age cycle. “The slow cooling trend is trivial compared to the warming that’s been happening and that’s in the pipeline,” said Kaufman, lead author of the study ( Revkin 2009 ). After a cooling of less than 0.5°F per millennium, the Arctic has warmed 2.2°F since 1900. “The fast rate of recent warming is the scary part,” said coauthor Jonathan T. Overpeck. “It means that major impacts on Arctic ecosystems and global sea level might not be that far off unless we act fast to slow global warming” ( Revkin 2009 ). “It’s basically saying that greenhouse gas emissions are overwhelming the system,” said coauthor David Schneider ( “Warming Past” 2009 ).

According to glaciologist Mark Serreze,

As temperatures warm in the Arctic and ice melts in the Arctic Ocean, forests of spruce trees and shrubs are spreading over northern Canada’s tundra at a rate much faster than anticipated by many climate models. A study in the Journal of Ecology, which used tree rings to date the year of establishment and death of spruce trees and reconstruct changes in tree line vegetation, analyzed the density and altitude of tree line forests in southwestern Yukon over the past three centuries ( “Canadian Tundra” 2007 ).

“The conventional thinking on tree line dynamics has been that advances are very slow because conditions are so harsh at these high latitudes and altitudes,” explained study author Ryan Danby, a biologist with the University of Alberta. “But what our data indicate is that there was an upslope surge of trees in response to warmer temperatures. It’s [as if] it waited until conditions were just right and then it decided to get up and run, not just walk” ( “Canadian Tundra” 2007 ).

“The tundra is becoming greener with the growth of more shrubs,” said Vladimir E. Romanovsky, a professor at the geophysical institute of the University of Alaska. This development is causing problems in some areas such as where herds of reindeer migrate. At the same time, there is some decrease in the greening of the northern forest areas, probably because of drought. The glaciers are continuing to shrink, and river discharge into the Arctic Ocean is rising, Romanovsky said ( Schmid 2006 ).

The Transpolar Drift is a strong Arctic current that runs from central Siberia to Greenland and then into the Atlantic and disperses pollutants. Could it stagnate in coming years as waters warm, leaving the area a polluted sea? This cold surface current was first discovered in 1893 by Norwegian explorer Fridtjof Nansen, who tried unsuccessfully to use it to sail to the North Pole. Together with the Beaufort Gyre, the Transpolar Drift keeps Arctic waters well mixed and ensures that pollution never lingers for long.

Without this current, the Arctic would retain such nuclear testing residues as strontium-90 and caesium-137, as well as pesticides and petroleum residue. Examining a business-as-usual greenhouse gas scenario, with carbon dioxide levels doubling by 2070, Y. Gao and colleagues (2009 , 375) found that the Transpolar Drift stops and the Beaufort Gyre, Greenland Current, and Gulf Stream weaken considerably. “One reason for this sluggish behaviour is a change in wind patterns driven by global warming and rapid melting of the Arctic sea ice” ( Ravilious 2009 ).

See also: Adaptation, Animals, Lizards, and Warming Habitats ; Animal Life, Arctic ; Arctic Hunters ; Atmospheric Circulation ; Climate Change, Abrupt Nature of ; El Niño and La Niña ; Inuit ; Permafrost ; Sea Ice, Arctic ; Summer Ice, Arctic ; Temperatures, Global ; Temperatures, Greenhouse Gas Levels and