Thus far, the Arctic has been ground zero for human-caused climate change. A combination of sea ice melt, albedo loss, a warming ocean that transports heat beneath a melting ice cap, regions of Jet Stream retreat into the far north, and an overburden of greenhouse gasses near the pole, among other factors, have all resulted in a very rapid pace of local warming.
(Global surface temperature anomaly over the last month features a high degree of, very visible, Arctic heat amplification. Most global warming models show the Arctic warms rapidly first under human warming. Then, as second stage warming progresses, heat begins to spike over other regions of the globe. Image source: NOAA ESRL.)
While global warming totals about .8 C above the 1880s average, about 1/6th the difference between now and another ice age, but on the side of hot, Arctic warming has pushed above 3.0 C during the same time period. And as the Arctic is warming four times as fast as the rest of the globe, many of human climate change’s most extreme impacts are now visible there.
The Arctic’s Massive and Dramatic Loss of Sea Ice
A primary measure of Arctic warming has been sea ice melt. And Arctic sea ice melt during the past few decades has been nothing if not dramatic. By end of summer 2012, a time when sea ice melt is most intense, area and extent totals had fallen more than 50% below their 1979 measurements. Meanwhile, Arctic sea ice volume, a measure of area + thickness, had fallen by as much as 80%. These losses are dramatic and raise the possibility for ice free summers, if the weather conditions line up, during a period between now and 2030.
Thin Ice Over Warming Water
As hinted at above, the Arctic has a number of unique characteristics that make it vulnerable to rapid warming in the context of a more slowly warming globe. And chief among these is geography — warmer continents surrounding a mostly frozen ocean.
A lion’s share of the northern polar ice cap area is composed of sea ice. By area, even after the stunning losses seen since 1979, the sea ice cap composes about 10.5 million square kilometers on average. Greenland, in contrast, only boasts an ice sheet of around 2 million square kilometers. This large layer of ice provides an amazing amount of cooling just due to its white, reflective properties. In the past, this albedo has helped to maintain a zone of very cold air centered almost directly over the pole.
But this Arctic system of cold amplification and northern refrigeration has a major Achilles heel. For the sea ice sits upon an ocean that is much closer to the melting point of water than any frozen land mass. Furthermore, all ocean systems are connected and, to one degree or another, readily transport heat.
(Melting Arctic sea ice during summer. Image source: NASA.)
In the context of human-caused warming, the majority of northern polar ice area is little more than a relatively thin layer sitting atop an ocean that is rapidly collecting atmospheric heat. A context that can result in rather dramatic consequences. In short, what this means is that northern polar ice sheet inertia isn’t quite so strong as was previously hoped.
A warming ocean eats away at the bottom ice. And as the thin, frozen ice layer of white, reflective ice is, at first gradually, and then more rapidly, replaced by dark, absorptive ocean the Arctic refrigerator breaks down and, increasingly, turns into a heat amplifier. A quickening pace of albedo loss means an even more rapid pace of warming for the ocean waters below. As warmth concentrates, more feedbacks come into play. Greenhouse gasses like methane and CO2 become liberated from the ice and also go to work in setting off warming. These feedbacks work in concert and, for a time, the Arctic heat rapidly amplifies.
Arctic heat amplification is now plainly visible in winter months when heat absorbed by a mostly ice-free Arctic Ocean during summer radiates up through thin and crack-riddled ice. In this way, heat bubbling up through the ice displaces cold, Arctic air southward, sparking off severe weather. An ongoing event that was particularly extreme during the winters of 2012-2013 and 2013-2014 when Arctic air first fled south over Europe and then the central and eastern United States (see polar vortex collapse).
An extended period of heat amplification has been the story of Arctic warming ever since the world began to heat up during the 1880s. A more moderate spurt of sea ice loss coincided with the growing Arctic warmth from the 1920s to the 1950s before stalling in the 60s and 70s, only to resume with a vengeance during the 1980s. Today, the extreme of Arctic heat amplification results in a number of rather severe knock-on effects that threatens everything from even larger Arctic greenhouse gas releases (methane, CO2) and severe changes to the Jet Stream that may well wreck the periods of relatively stable weather human beings in the north have been used to for 10,000 years running.
Antarctic — Vast Continental Ice Sheets Surrounded By Oceans
Moving southward into the still frozen austral regions, we find a geography and related pace of climate change that is markedly different. Here the vast glaciers pile atop a Continent that has now been buried and frozen for millions and millions of years. The cold is locked into ice sheets that reach thousands of feet in height, cover an area of nearly 14 million square kilometers, and plunge deep into the long-frozen Earth. If the ice in the Arctic is merely a thin facade covering warmer oceans, the Antarctic ice is a thick fortress atop adamant and frozen earth.
The degree of inertia this represents for human-caused climate change is, therefore, much greater than what we see up north. And though the Antarctic fortress is far from impenetrable to the radically strong assaults of human warming, it will resist their insults for longer, giving way its great piles of ice in a more ablative fashion with, likely, even more stark and shocking results.
This densely frozen geography coming into conflict with human-caused warming has resulted in far-reaching, though less visible, impacts. Overall, largely due to the heat-insulation effect of Antarctica, southern hemisphere warming has progressed far more slowly than warming in the north. Here the battle is one of inches in which regions closer to the equator, such as Australia and the equatorial oceans, show the highest rates of warming. Meanwhile, Antarctica has remained, for the most part, a bastion of cold with increasingly intense wind fields isolating it from the more rapidly warming regions. In this case, and in contrast to the Northern Hemisphere Jet Stream, the upper level winds surrounding the South Pole have strengthened even as they have slowly receded.
(Antarctica surrounded by storms on March 2 of 2014 as a combination of austral summer and human warming shove the Southern Hemisphere Jet Stream toward the pole. Image source: Lance-Modis.)
Such a recession resulted in very hot, dry weather for southern Australia as equatorial heat shoved the strong winds and related storms ever southward. Meanwhile, increased rates of evaporation held in check the benefits of equatorial rain expansion into northern regions. Only the occasional challenge to this new, retreating Jet Stream, breaks the pattern of expanding drought in the south with extraordinary precipitation and storm events. And so Australia has suffered a series of worst droughts and fires on record interrupted by brief but very intense rain events over the past decade.
While the vast ice sheets of Antarctica have, so far, served as a buttress against atmospheric warming even as the Jet Stream retreated southward, heat in the ocean again went to work. Though mostly protected by vast and frozen continental lands to the west, the more northerly segment of East Antarctica featured large sections of submerged continents upon which rested immense, sea terminating ice sheets. Some of these great ice sheets had sections submerged hundreds of feet below sea level. And though the surface waters only gradually warmed, deeper down, the story was much different.
The endless calving of Antarctica’s glaciers sends off thousands of ice bergs from the shores of Antarctica each year. This massive calving cools the surface waters near Antarctica through both the melting of these frozen hills and mountains as well as the chilling effect they have on nearby air currents. As such, cold waters continually flow out from Antarctica. But even these waters have been impacted by human caused climate change, grudgingly increasing in temperature over the decades.
(Pine Island Glacier calves into the Amundsen Sea. A recent study found this large ice sheet was in the first stages of irreversible collapse. Image source: iSTAR-NERC.)
If the cold surface waters surrounding Antarctica have warmed only slowly, the story of the depths is somewhat different. Down-welling warmer and saltier waters contacting the Antarctic Circumpolar Current create a growing pool of warmth extending to the Antarctic Continental Shelf boundary. There, water circulation dynamics cause the warm water in the abyss to up-well even as it contacts the ocean terminating polar ice sheets.
The warm water thus eats away at the undersides of these ice sheets, causing increasing instability in some of the most vulnerable regions of West Antarctica. This heat transfer from the ocean depths has set off a significant erosion in a number of very large ice sheets and is now spurring the massive Pine Island Glacier (PIG) into an unstoppable rush to the sea.
Models Show Antarctic Sea Ice to Rapidly Decline through Mid Century
If Antarctic warming has been more subtle than the explosive heat amplification of northern regions, it is no less ominous. At the very least, it resulted in locking in 1-2 meters of sea level rise through irreversible ice sheet collapse spurred by warm water upwelling and now puts at risk many more meters of eventual increases to follow.
But, at the surface of the waters, despite a period of slowly rising warmth, the buffer zone of Antarctic sea ice has remained somewhat stable since 1979, even showing periods of moderate increase in overall area and extent. As described above, this is in marked contrast to a stunning collapse of Northern Hemisphere sea ice. A contrast that has served as foil for much debate over the ongoing impacts of human warming even as it was exploited as fodder by climate change deniers, when they weren’t out chasing the most recent snowstorm.
(Antarctic sea ice area anomaly since 1979 shows a slight increase in overall coverage, primarily due to a counter-trend increase in Ross Sea ice coverage. New studies show Antarctic sea ice is now set to rapidly decline. Image source: Cryosphere Today.)
Looking more closely, though, one finds that the current expansion of Antarctic sea ice may well be very precarious. For of the three embayments containing Antarctic sea ice only one — the Ross Sea — has shown sea ice growth in recent years. The other two have either remained stable or shown slow recession.
Polar researchers had attributed the moderate net expansion of southern sea ice to a combination of increasingly strong winds spreading out Ross ice flows during winter, a freshening of surface waters through the ongoing melt of Antarctica’s ice sheets that increases the melt temperature of ice and thus encourages its formation, and to changes to ocean currents and rates of precipitation. Now, a new study conducted by researchers at the Virginia Institute of Marine Science has found that this relative period of Ross sea ice stability and growth is about to end.
Warmth About to Crash Through Antarctica’s Gates
The various fragile conditions that have conspired to expand Ross Sea ice are now about to collapse under an onrush of increasing temperatures. For according to a new study entitled The Effects of Changing Winds and Temperatures on the Oceanography of the Ross Sea During the 21rst Century high resolution climate models show both increasing temperatures and rapidly melting ice in this critical and climatologically sensitive region under a regime of business as usual fossil fuel emissions.
According to the study’s authors:
We examined the effects of projected changes in atmospheric temperatures and winds on aspects of the ocean circulation likely important to primary production using a high-resolution sea ice–ocean–ice shelf model of the Ross Sea. The modeled summer sea ice concentrations decreased by 56% by 2050 and 78% by 2100.
In short, the bounding Jet Stream, the insulating continental Antarctic ice, and the cold surface waters surrounding the continent can’t keep out an ever increasing level of human-caused warming indefinitely. Over the coming decades this warmth will pulse higher in the region surrounding Antarctica with profound impacts to sea ice, resulting in a more than 50% reduction by 2050 and a 78% reduction by 2100.
The study also found that:
The ice-free season also grew much longer, with the mean day of retreat in 2100 occurring 11 days earlier and the advance occurring 16 days later than now.
In essence, the spring and summer melt season throughout the Antarctic region was shown to extend nearly one month longer than today’s period of melt and warmth. Such an expansion of heat intensity and duration will have profound impacts not only for sea ice, but for land ice and for life in the oceans as well.
Mixing Layers Reduced, Large Phytoplankton Blooms to Follow
Perhaps less visible but somewhat more ominous are ocean changes that are projected as Antarctic sea ice goes into rapid decline. Study authors found that ocean mixing over the region would fall by 12% by 2050 and a remarkable 44% by 2100. This dramatically increased stratification would, at first, result in very large blooms of phytoplankton as the surface waters see far more oxygen and the depths become ever-more deprived. This riot of microbial life may seem a positive development for the Ross Sea. But, if anything, it is a sign of oceanic productive zones moving southward to the polar region.
More ominous is the impact on krill and larger animals dependent on these small swimmers. Sea ice is critical to the survival of many krill species. And with its decline, these marine animals are likely to be negatively impacted.
According to lead author, Dr. Walker Smith:
our results suggest that phytoplankton production will increase and become more diatomaceous. Other components of the Ross Sea food web will likely be severely disrupted, creating significant but unpredictable impacts on the ocean’s most pristine ecosystem.