Most Americans associate fall with football and raking leaves, but in the Arctic this season is about ice. Every year, floating sea ice in the Arctic thins and melts in spring and summer, then thickens and expands in fall and winter.
As climate change warms the Arctic, its sea ice cover is declining. This year scientists estimate that the Arctic sea ice minimum in late September covered 1.77 million square miles (4.59 million square kilometers), tying the sixth lowest summertime minimum on record.
With less sea ice, there is burgeoning interest in shipping and other commercial activity throughout the Northwest Passage – the fabled route that links the Atlantic and Pacific oceans, via Canada’s convoluted Arctic archipelago – as well as the Northern Sea Route, which cuts across Russia’s northern seas. This trend has serious potential impacts for Arctic sea life.
In a recent study, we assessed the vulnerability of 80 populations of Arctic marine mammals during the “open-water” period of September, when sea ice is at its minimum extent. We wanted to understand the relative risks of vessel traffic across Arctic marine mammal species, populations and regions. We found that more than half (53 percent) of these populations – including walruses and several types of whales – would be exposed to vessels in Arctic sea routes. This could lead to collisions, noise disturbance or changes in the animals’ behavior.
Less ice, more ships
More than a century ago, Norwegian explorer Roald Amundsen became the first European to navigate the entire Northwest Passage. Due to the short Arctic summer, it took Amundsen’s 70-foot wooden sailing ship three years to make the journey, wintering in protected harbors.
Fast-forward to summer 2016, when a cruise ship carrying more than 1,000 passengers negotiated the Northwest Passage in 32 days. The summer “open-water” period in the Arctic has now increased by more than two months in some regions. Summer sea ice cover has shrunk by over 30 percent since satellites started regular monitoring in 1979.
Arctic seas are home to a specialized group of marine mammals found nowhere else on Earth, including beluga and bowhead whales, narwhals, walruses, ringed and bearded seals and polar bears. These species are critical members of Arctic marine ecosystems, and provide traditional resources to Indigenous communities across the Arctic.
According to ecologists, all of these animals are susceptible to sea ice loss. Research at lower latitudes has also shown that marine mammals can be affected by noise from vessels because of their reliance on sound, as well as by ship strikes. These findings raise concerns about increasing vessel traffic in the Arctic.
Sensitivity times exposure equals vulnerability
To determine which species could be at risk, we estimated two key factors: Exposure – how much a population’s distribution overlaps with the Northwest Passage or Northern Sea Route during September – and sensitivity, a combination of biological, ecological and vessel factors that may put a population at a higher risk.
As an illustration, imagine calculating vulnerability to air pollution. People generally are more exposed to air pollution in cities than in rural areas. Some groups, such as children and the elderly, are also more sensitive because their lungs are not as strong as those of average adults.
We found that many whale and walrus populations were both highly exposed and sensitive to vessels during the open-water period. Narwhals – medium-sized toothed whales with a large spiral tusk – scored as most vulnerable overall. These animals are endemic to the Arctic, and spend much of their time in winter and spring in areas with heavy concentrations of sea ice. In our study, they ranked as both highly exposed and highly sensitive to vessel effects in September.
Narwhals have a relatively restricted range. Each summer they migrate to the same areas in the Canadian high Arctic and around Greenland. In fall they migrate south in pods to offshore areas in Baffin Bay and Davis Strait, where they spend the winter making deep dives under the dense ice to feed on Greenland halibut. Many narwhal populations’ core summer and fall habitat is right in the middle of the Northwest Passage.
Vulnerable Arctic regions, species and key uncertainties
The western end of the Northwest Passage and the eastern end of the Northern Sea Route converge at the Bering Strait, a 50-mile-wide waterway separating Russia and Alaska. This area is also a key migratory corridor for thousands of beluga and bowhead whales, Pacific walruses and ringed and bearded seals. In this geographic bottleneck and other narrow channels, marine mammals are particularly vulnerable to vessel traffic.
Among the species we assessed, polar bears were least vulnerable to September vessel traffic because they generally spend the ice-free season on land. Of course, longer ice-free seasons are also bad for polar bears, which need sea ice as a platform for hunting seals. They may also be vulnerable to oil spills year-round.
Research in the harsh and remote Arctic seas is notoriously difficult, and there are many gaps in our knowledge. Certain areas, such as the Russian Arctic, are less studied. Data are sparse on many marine mammals, especially ringed and bearded seals. These factors increased the uncertainty in our vessel vulnerability scores.
We concentrated on late summer, when vessel traffic is expected to be greatest due to reduced ice cover. However, ice-strengthened vessels can also operate during spring, with potential impacts on seals and polar bears that are less vulnerable in September. The window of opportunity for navigation is growing as sea ice break-up happens earlier in the year and freeze-up occurs later. These changes also shift the times and places where marine mammals could be exposed to vessels.
Planning for a navigable Arctic
Recent initiatives in the lower 48 states offer some models for anticipating and managing vessel-marine mammal interactions. One recent study showed that modeling could be used to predict blue whale locations off the California coast to help ships avoid key habitats. And since 2008, federal regulations have imposed seasonal and speed restrictions on ships in the North Atlantic to minimize threats to critically endangered right whales. These practical examples, along with our vulnerability ranking, could provide a foundation for similar steps to protect marine mammals in the Arctic.
The International Maritime Organization has already adopted a Polar Code, which was developed to promote safe ship travel in polar waters. It recommends identifying areas of ecological importance, but does not currently include direct strategies to designate important habitats or reduce vessel effects on marine mammals, although the organization has taken steps to protect marine habitat in the Bering Sea.
Even if nations take rigorous action to mitigate climate change, models predict that September Arctic sea ice will continue to decrease over the next 30 years. There is an opportunity now to plan for an increasingly accessible and rapidly changing Arctic, and to minimize risks to creatures that are found nowhere else on Earth.
Donna Hauser, Research Assistant Professor, International Arctic Research Center, University of Alaska Fairbanks; Harry Stern, Principal Mathematician, Polar Science Center, University of Washington, and Kristin Laidre, Associate Professor of Aquatic and Fishery Sciences, University of Washington
The Arctic has been unusually warm since the beginning of 2018. In the past week air temperatures have hovered around 20℃ above normal or even higher. On February 25, the Cape Morris Jesup weather station in northern Greenland recorded 6.1℃, despite the fact that at this time of year, when the sun is still below the horizon, temperatures are typically around -30℃.
A surprising feature of this warming event was how far into (and beyond) the Arctic it has penetrated. Warm air migrated north from the Atlantic Ocean, over the North Pole and towards the Pacific Ocean, bringing above-freezing air temperatures to large areas of the Arctic Ocean for more than 24 hours.
We have not seen a warm intrusion from the Atlantic Ocean on this scale since at least 1980.
Is this unprecedented?
Warm events in the middle of the northern winter are not unheard of. Large winter storms can bring strong winds that pump warm air into the Arctic from lower latitudes.
For example, during the Norwegian explorer Fridtjof Nansen’s 1896 expedition aboard the icebreaker Fram, the crew observed temperatures of -3℃ on one midwinter’s day. More recently, in December 2015, an Arctic warming event brought temperatures of 2℃ to the North Pole, and the warm weather continued into early 2016.
But, crucially, this type of event is becoming more common and longer in duration, with higher peak temperatures.
Record low sea ice extent
February 26 brought a new record low for sea ice extent: maximum sea ice extent on that day was 14.20 million square kilometres, which is 1.29 million km2 below the 1981-2010 average for that day. This follows several years with record low winter maximum sea ice extents in 2015, 2016 and 2017.
The current warm conditions in the Arctic have implications for sea ice year-round. Sea ice grows in winter and melts in summer. The warm air temperatures will slow down sea ice growth, and strong winds will push it around, breaking it up in places – as happened north of Greenland earlier this week.
Open water where the ice is broken will release extra heat into the atmosphere. By the time the spring sun comes around, the sea ice pack is thinned and weakened, and may melt more easily.
Cold weather in Europe
While the Arctic has been hot, Europe has been bitterly cold this week: London recorded -6℃; Berlin reached -14℃; and the Alps plunged to -27℃. Rome received 5-15cm of snow on Monday, and up to 40cm of snow fell in Britain on Wednesday.
It might sound counter-intuitive, but this cold weather is directly linked to the recent warming event in the Arctic.
Normally, the cold air above the polar region is contained in the Arctic by a ring-like band of strong winds called the polar vortex. But in the middle of February this year, the polar vortex split into two vortices: one over Eurasia and the other over North America.
Between these two features, a strong high-pressure system gradually formed. As a result, warm air was pumped up into the Arctic on the west side of the high, while cold air was channelled southwards to the east of it. Hence the exceptionally warm air in the Arctic and the cold snap in Europe.
Is the polar vortex changing?
The polar vortex is driven by the strong temperature differences between the warm mid-latitudes and the cold Arctic. With the Arctic warming more rapidly than the mid-latitudes, this temperature difference is decreasing and some scientists believe that the polar vortex is weakening.
Research suggests that the polar vortex has become “wavier” as a result of this weakening. A wavier jet stream would lead to more frequent cold outbreaks of polar air at lower latitudes, and at the same time cause warm air to intrude into the Arctic. However, other researchers have argued that “large uncertainties regarding the magnitude of such an influence remain”.
Generally speaking, warming at every latitude makes cold spells at low latitudes less likely, and warm intrusions at high latitudes more likely, unless the Arctic warming leads to a fundamental change in the dynamics of the atmosphere.
Since 1979, Arctic warming events have grown more frequent. However, climate projections indicate that there will be fewer Arctic storms in the latter part of this century, and thus fewer Arctic warming events.
As scientists, we were startled by the extent of this week’s Arctic warming, and will be working hard to understand the short- and long-term implications. All eyes will be on the upcoming maximum winter Arctic sea ice extent, which is likely to happen in the next few weeks and could possibly set a new record low.
Amelie Meyer, Postdoctoral Researcher, Physical Oceanography, Norwegian Polar Institute; Erik W. Kolstad, Research professor, Uni Research; Mats Granskog, Senior research scientist, Norwegian Polar Institute, and Robert Graham, Postdoctoral Researcher, Climate Modelling, Norwegian Polar Institute