The polar bear has become a symbol of climate change. But while researchers and politicians continue to merely debate rather than act: How is the king of the Arctic doing?
The arctic summer was already quite far advanced. Not a single ice floe floated off the coasts of Spitsbergen; all the sea ice had been melting for weeks, and the ice charts on the cruise ships around the almost deserted High Arctic archipelago showed the pack-ice limit a good two hundred kilometres further north from here. It had always been like this in the last few years in late August: the islands of Spitsbergen were now, at the end of the Arctic summer, in an ice-free sea. – Surely it must have been an enormous feeling of hunger that had prompted the mighty, scruffy-looking male polar bear on the tundra in Woodfjord to approach the few eider ducks on the shore with all due caution.
For two months, maybe even three or more, this polar bear hadn’t been able to get anything into his huge stomach. Somehow it had missed the “boat” early in the summer. The icy sea had begun to thaw, but it failed to keep up with the ice edge shifting northward – and suddenly found himself stuck on the blossoming tundra. A summer without food! The fat seals, the polar bear’s favourite food, were where the ice was now.
Despite its imposing bulk, the polar bear managed to maneuver within a few dozen meters of the waterfowl. The resting eiders didn’t seem to notice the danger until the bear made a mighty sprint with the last of its strength. In a flash the ducks scattered and flew away – except for one; it was still molting and therefore unable to fly. A bear’s paw whizzed down on it with brute force, several times, again and again, until hardly anything remained of the flat-knocked duck in the hole in the ground that was forming. The polar bear did not want to miss this prey, an amuse bouche only, a tiny appetizer for a bear’s stomach that could easily hold 70 kilograms at once.
Scenes like this one from Woodfjord in Spitsbergen are becoming increasingly common elsewhere in the Arctic as global warming heats up the northern polar region. The polar bears’ very own habitat, the ice of the Arctic Ocean, is practically melting away under their paws. As an ice-dwelling hunter, the polar bear depends on the pack ice. Its main prey, bearded and ringed seals, it only gets hold of there, at the breathing holes of the seals. In the mostly ice-free summer, however, when its food can literally swim away, fasting is the order of the day. Then everything that seems edible is on the menu of the carnivorous polar bear, the largest land predator on earth. Birds and their eggs, seaweed, carrion, municipal waste etc. have to be used to somehow get a polar bear through the difficult summer period.
Research by transmitter
Since the polar bear separated from the brown bear less than 500,000 years ago and evolved into a separate species, Ursus maritimus, the “sea bear”, has depended on the pack ice in the Arctic Ocean. Thus it has conquered probably the most extreme habitat of this earth, because the ice of the sea changes constantly. It melts and freezes again, it breaks up, shifts, or piles up into meter-high press ice ridges. This is the stage of life for the less than 20,000 polar bears that exist today. Only here they find their food, only here they manage to meet a mating partner and to raise their young.
Gleamingly bright in the months of perpetual daylight in summer and bitterly cold, dark in the month-long polar night – anyone who calls the endless expanse of ice of a frozen sea their home must be good on their feet. Polar bears are indeed constantly on the move. Although the pack ice appears to offer no clues from a human perspective, polar bears do not simply wander aimlessly. In more recent studies, zoologists are increasingly taking advantage of a satellite transmitter. In this way, the researchers succeed in tracking polar bears for months and evaluating their movement patterns on the ice. Amazing what comes out of that! There are polar bears that have been shown to travel between 3300 and 7100 kilometres in a year. During their lonely hikes over the ice, the bears also stay in an ancestral action area (home range), the borders of which they rarely cross. Such an activity area, the icy realm of the King of the Arctic, often measures between 100,000 and 340,000 square kilometres.
And what does a polar bear do on its long migratory journeys?
Pack ice and ice bridges
The search for the breathing holes of seals, where at some point the longed-for food in the form of a tasty bearded or ringed seal must appear, is one thing. The other is for reproduction: as solitary animals, polar bears have to search for each other on the pack ice between March and May to produce offspring. Thanks to its outstanding smelling-fortune, males can take up the smell of mating-ready females already over many kilometers and follow the scent-track. Even in such a phase of life applies: without pack ice – no mating.
For pregnant female polar bears, and later for their cubs, the sea ice cover (and snow) also plays an important role. Most pregnant female polar bears in the Arctic visit certain land areas at the beginning of winter to wait for sufficient snow and then dig their den in the drifting snow.
Only if the sea freezes in time and sufficiently, the future polar bear mothers can reach such birthing centres, such as the Kong-Karls Islands in Spitsbergen, Wrangel Island or Franz-Josef-Land in the Russian Arctic, easily and in an energy-saving way via the ice bridge. And only when there is enough snow of optimal quality do the female bears manage to build a birthing den that will last until next spring. The importance of the timing of freezing is shown by the example of the small island of Hopen in the southeast of Spitsbergen: if the sea freezes over too late in autumn, the pregnant females do not come to Hopen to give birth. The extent to which the ice has retreated from the land areas over the course of the summer is in turn largely determined by how strongly and quickly the sea has thawed during the summer. The current climatic development worldwide will not only be difficult for the polar bears with regard to the accessibility of their den areas. Nothing is the same when it comes to Arctic snow either, an important component in constructing a durable, well-insulated nursery. Snow, of course, must fall in sufficient quantity. If it falls abundantly and at the right time, and the wind blows it together to deep drifts at the lee-sides of terrain-unevenness, only then, the optimal conditions for the construction of a den are given.
While most female polar bears around the North Pole prefer the “cube den on land” variety, there are deviants from this norm in the Beaufort Sea. There, in the Arctic Ocean off the coasts of northern Alaska and Canada, many of the pregnant females stay right on the sea ice. They choose snow caves on drifting pack ice and on coastal fast ice.
Snow must stay
But this natural need of polar bears in the Beaufort Sea has been disrupted by global warming. Zoologists have found that the number of female bears digging their den on the pack ice has declined from 62% to 37% over the past two decades. The reason for this is on the one hand the time lag with which the sea freezes over in autumn, and on the other hand the poorer ice quality. This leads to the fact that the pack ice no longer piles up so optimally to form press ice ridges or other irregularities. However, in order for the wind-blown snow to accumulate high enough, it must be able to deposit on obstacles on the pack ice. It is therefore not surprising that in the autumn of each of the past few years there have never been more polar bears sighted on the shores of the Beaufort Sea than today. If the trend continues and valuable polar bear habitat continues to melt away, it is likely that the approximately 2800 polar bears in the Beaufort Sea region will become extinct within the next few decades.
In a study, Canadian zoologists investigated how the litter size of polar bears will develop in the future. Polar bears on western Hudson Bay in the early 1990s served as the basis for the calculation model. At that time, almost 30% of the female bears there failed to reproduce for energetic reasons (lack of food).
Now, if the ice were to break up a month earlier as a result of global warming, the study found, between 40 and about 70% of the female bears in western Hudson Bay would be unable to give birth or raise cubs.
The scenario is even worse if the ice melts two months earlier: half to all female bears would lose their cubs for lack of available seals. At the same time, the average litter size would be reduced by one to two thirds in the first case and by half to 100% in the second case.
However, this simply means that the polar bear subpopulation on western Hudson Bay will not survive under the current future outlook.
Researchers believe that more than one-third of all polar bears in the Arctic are likely to experience similar effects because the opportunity to forage (and store energy) on the ice is shortened and the time spent fasting on land is extended.
Ice becomes scarce
When the pack ice thaws earlier than usual and the sea freezes over later in the year, the time during which polar bears can hunt seals is shortened. Pregnant females then have trouble gorging themselves on the urgently needed fat-stock for the long time in the dens. And female bears with cubs emerging from their dens in the spring are less likely to find seal pups – actually the power food for the little polar bears – when ice conditions are unfavorable.
Because what little ice there is melts away much faster in the warmer summers, many polar bears have to stay on land longer, virtually without food. However, those bears that remain on the sea ice during the summer are shipped with the ice to far northern areas, where there are fewer (or no!) seals, due to rapid melting.
The earlier and easier the closed pack ice cover breaks up into individual floes (drift ice), the more frequently large open water areas occur. Although the polar bear is an excellent swimmer as a marine mammal, long and frequent swims drain its energy. For the offspring in the first months of life, wide water channels in the ice are deadly – the little ones cannot swim in the cold water for too long.
The Arctic pack ice, a fascinating, extreme habitat, an interconnected ecosystem, is in distress. Many recent observations across the Arctic make it clear that the 2007 Intergovernmental Panel on Climate Change report drastically underestimated the rate at which Arctic sea ice is melting.
These three major changes in sea ice threaten the lives of polar bears:
– Rapid decrease of the summer minimum extent – In September, the summer melting of sea ice reaches its peak. This is when the ice cover in the Arctic Ocean is naturally at its lowest, before it increases again shortly afterwards due to the renewed freezing in autumn and winter. This minimum sea ice extent measured in September is decreasing dramatically (currently 13% per decade) because more ice is melting away in summer than ever before. If this continues at the same pace, the Arctic Ocean will remain virtually ice-free in summer in 30 or 40 years. A cautionary example: In 2008, the sounds and passages of the Northeast Passage and, at the same time, the Northwest Passage were practically ice-free – for the first time in history.
Lowest ice extent in September in million km2 and decrease in % compared to long-term mean (1981-2010):
2016 4,53 -29 %
2017 4,82 -25 %
2018 4,79 -25 %
2019 4,36 -32 %
2020 3,92 -39 %
– Loss of perennial sea ice – Although large areas of the Arctic Ocean have been freezing in winter and thawing in summer since time immemorial, large parts of this polar sea have always remained covered by ice that has resisted one or more summer thawing processes and thus become perennial ice over time. Today, hardly any older sea ice can be found, and old ice that has lasted five or more summers has almost completely disappeared from the Arctic.
– Reduced thickness of the pack ice – The average thickness of the ice cover over the Arctic Ocean was 3.64 metres in 1980. Since then, it has decreased by 1.75 metres and is reported to be 1.89 metres for 2008 – and an average sea ice thickness of only 1.25 metres was determined for 2012.
Tragic changes are also underway in other forms of ice in the Arctic. For example, the temperature of permafrost, or permafrost ground, has increased by 2°C, and the southern boundary of Arctic permafrost has shifted northward in Russia and Canada.
It’s getting warm in the Arctic
Feeding, mating, giving birth – polar bears depend on their pack ice at every stage of life. Without this icy cap, which covers up to 15 million square kilometres of the Arctic Ocean in winter, polar bears cannot survive – and with them numerous other marine mammals for which sea ice is the key to life. They include the walrus and other seal species, as well as cetaceans such as the beluga/white whale and the narwhal.
Global climate warming will hit the Arctic particularly hard. The north polar region will warm twice as much as the rest of the world. Winter temperatures are predicted to rise by up to 7°C by 2080.
Recent reconstructions of the prehistoric Arctic climate show that summer temperatures in the Arctic have been higher during the last few decades than at any time in the past two thousand years. The six years between 2005 and 2010 alone produced the warmest temperatures ever recorded in the Arctic.
Higher air temperatures lead to more precipitation in the Arctic: The fifth wettest months since 1950 all occurred during the last decade. The years after 2000, and especially since 2004, have been particularly wet. In winter or early spring, when it rains recently on the snow caves where the polar bears have thrown their cubs, the cave can collapse. Climatologists predict that precipitation in the Arctic will increase by about 20%.
But it’s not just the rain that’s affecting the female bears’ dens – there’s more and more often a lack of sufficient snow to build such dens!
Until now, the Arctic landscape had been covered by snow for eight to ten months of the year. However, the duration of this snow cover is also decreasing – it snows later, it thaws earlier, and on average the snowmelt in the land areas of the Arctic starts almost 14 days earlier today than in the 1970s. In addition, the snow remains in fewer and fewer areas – the snow-covered area in the Arctic has decreased by almost one fifth in the last fifty years.
Melting ice, warm spells, rain, as if such climatic changes in the Arctic did not already mean bad news for the polar bear – there is an even more perfidious threat. That moulting eider duck that our ravenous polar bear caught in Woodfjord in Spitzberg and knocked flat with hunting zeal had absorbed environmental toxins into its body.
As remote as the Arctic may seem on a globe, this region is not immune to a chemical shower from our latitudes. The polar bear, however, is enthroned at the top of the polar food chain – in its body the pollutants such as mercury, PCB’s, dioxins, DDT etc. accumulate in elevated concentrations. If polar bears had to fast for longer and longer periods due to global warming, they would be increasingly exposed to long-lived organic pollutants, which would then be released from their own fatty tissue. The king of the Arctic would poison himself from within. But this is another sad story.
Text: Peter Balwin
Photos: Heiner Kubny