Arctic ice loss is worrying, but the giant stirring in the South could be even worse

Field camp on the East Antarctic ice sheet.
Nerilie Abram

Nerilie Abram, Australian National University; Matthew England, UNSW, and Matt King, University of Tasmania

A record start to summer ice melt in Greenland this year has drawn attention to the northern ice sheet. We will have to wait to see if 2019 continues to break ice-melt records, but in the rapidly warming Arctic the long-term trends of ice loss are clear.

But what about at the other icy end of the planet?

Antarctica is an icy giant compared to its northern counterpart. The water frozen in the Greenland ice sheet is equivalent to around 7 metres of potential sea level rise. In the Antarctic ice sheet there are around 58 metres of sea-level rise currently locked away.

Like Greenland, the Antarctic ice sheet is losing ice and contributing to unabated global sea level rise. But there are worrying signs Antarctica is changing faster than expected and in places previously thought to be protected from rapid change.

The threat from beneath

On the Antarctic Peninsula – the most northerly part of the Antarctic continent – air temperatures over the past century have risen faster than any other place in the Southern Hemisphere. Summer melting already happens on the Antarctic Peninsula between 25 and 80 days each year. The number of melt days will rise by at least 50% when global warming hits the soon-to-be-reached 1.5℃ limit set out in the Paris Agreement, with some predictions pointing to as much as a 150% increase in melt days.

But the main threat to the Antarctic ice sheet doesn’t come from above. What threatens to truly transform this vast icy continent lies beneath, where warming ocean waters (and the vast heat carrying capacity of seawater) have the potential to melt ice at an unprecedented rate.

Read more:
New findings on ocean warming: 5 questions answered

Almost all (around 93%) of the extra heat human activities have caused to accumulate on Earth since the Industrial Revolution lies within the ocean. And a large majority of this has been taken into the depths of the Southern Ocean. It is thought that this effect could delay the start of significant warming over much of Antarctica for a century or more.

However, the Antarctic ice sheet has a weak underbelly. In some places the ice sheet sits on ground that is below sea level. This puts the ice sheet in direct contact with warm ocean waters that are very effective at melting ice and destabilising the ice sheet.

Scientists have long been worried about the potential weakness of ice in West Antarctica because of its deep interface with the ocean. This concern was flagged in the first report of the Intergovernmental Panel on Climate Change (IPCC) way back in 1990, although it was also thought that substantial ice loss from Antarctica wouldn’t be seen this century. Since 1992 satellites have been monitoring the status of the Antarctic ice sheet and we now know that not only is ice loss already underway, it is also vanishing at an accelerating rate.

The latest estimates indicate that 25% of the West Antarctic ice sheet is now unstable, and that Antarctic ice loss has increased five-fold over the past 25 years. These are remarkable numbers, bearing in mind that more than 4 metres of global sea-level rise are locked up in the West Antarctic alone.

Antarctic ice loss 1992–2019, European Space Agency.

Read more:
Antarctica has lost nearly 3 trillion tonnes of ice since 1992

Thwaites Glacier in West Antarctica is currently the focus of a major US-UK research program as there is still a lot we don’t understand about how quickly ice will be lost here in the future. For example, gradual lifting of the bedrock as it responds to the lighter weight of ice (known as rebounding) could reduce contact between the ice sheet and warm ocean water and help to stabilise runaway ice loss.

On the other hand, melt water from the ice sheets is changing the structure and circulation of the Southern Ocean in a way that could bring even warmer water into contact with the base of the ice sheet, further amplifying ice loss.

There are other parts of the Antarctic ice sheet that haven’t had this same intensive research, but which appear to now be stirring. The Totten Glacier, close to Australia’s Casey station, is one area unexpectedly losing ice. There is a very pressing need to understand the vulnerabilities here and in other remote parts of the East Antarctic coast.

The other type of ice

Sea ice forms and floats on the surface of the polar oceans. The decline of Arctic sea ice over the past 40 years is one of the most visible climate change impacts on Earth. But recent years have shown us that the behaviour of Antarctic sea ice is stranger and potentially more volatile.

The extent of sea ice around Antarctica has been gradually increasing for decades. This is contrary to expectations from climate simulations, and has been attributed to changes in the ocean structure and changing winds circling the Antarctic continent.

But in 2015, the amount of sea ice around Antarctica began to drop precipitously. In just 3 years Antarctica lost the same amount of sea ice the Arctic lost in 30.

Read more:
Why Antarctica’s sea ice cover is so low (and no, it’s not just about climate change)

So far in 2019, sea ice around Antarctica is tracking near or below the lowest levels on record from 40 years of satellite monitoring. In the long-term this trend is expected to continue, but such a dramatic drop over only a few years was not anticipated.

There is still a lot to learn about how quickly Antarctica will respond to climate change. But there are very clear signs that the icy giant is awakening and – via global sea level rise – coming to pay us all a visit.The Conversation

Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University; Matthew England, Australian Research Council Laureate Fellow; Deputy Director of the Climate Change Research Centre (CCRC); Chief Investigator in the ARC Centre of Excellence in Climate System Science, UNSW, and Matt King, Professor, Surveying & Spatial Sciences, School of Technology, Environments and Design, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.


As Arctic ship traffic increases, narwhals and other unique animals are at risk

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A pod of narwhals (Monodon monoceros) in central Baffin Bay. Narwhals are the most vulnerable animals to increased ship traffic in the Arctic Ocean.
Kristin Laidre/University of Washington, CC BY-ND

Donna Hauser, University of Alaska Fairbanks; Harry Stern, University of Washington, and Kristin Laidre, University of Washington

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.

Map of the Arctic region showing the the Northern Sea Route and Northwest Passage.
Arctic Council/Susie Harder

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.

Bowhead whale (Balaena mysticetus) in Disko Bay, West Greenland.
Kristin Laidre, CC BY

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.

Ringed seal (Pusa hispida) pup in Alaska.

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.

A pod of narwhals (Monodon monoceros) in central Baffin Bay. Narwhals are the most vulnerable animals to increased ship traffic in the Arctic during September.
NOAA/OAR/OER/Kristin Laidre

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.

The Arctic Ocean is covered with floating sea ice in winter, but the area of sea ice in late summer has decreased more than 30 percent since 1979. The Arctic Ocean is projected to be ice-free in summer within decades.

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.The Conversation

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.