Interactive: When will the Arctic see its first ice-free summer?

Words by Daisy Dunne. Design by Tom Prater.

Inside MOSAiC

The world’s largest polar research expedition is currently underway in the Arctic. The year-long expedition, known as the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), involves 300 researchers from 19 countries. From a ship trapped in the sea ice, scientists are taking measurements that could help to transform climate models. Carbon Brief’s science writer Daisy Dunne joined the expedition for its first six weeks in the autumn of 2019. This is the second of four articles focused on the MOSAiC expedition.

Since satellites first began monitoring the Arctic in 1979, the average area covered by sea ice has shrunk by at least 40%. The average thickness of the ice has fallen by more than half over the same time period.

These rapid changes have left climate scientists facing an urgent question: when will Arctic sea ice disappear?

The pace of change is most stark in September, the end of summertime in the Arctic. Each year, Arctic sea ice goes through a seasonal cycle, growing in area and thickness through the cooler winter months before shrinking back again as temperatures rise in the spring and summer.

The point at the end of summer when sea ice reaches its lowest level for the year is known as the “sea ice summer minimum”. This year, the sea ice minimum is the second smallest on record, beaten only by the sea ice low seen in 2012.

Inside MOSAiC

The world’s largest polar research expedition is currently underway in the Arctic. The year-long expedition, known as the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), involves 300 researchers from 19 countries. From a ship trapped in the sea ice, scientists are taking measurements that could help to transform climate models. Carbon Brief’s science writer Daisy Dunne joined the expedition for its first six weeks in the autumn of 2019. This is the second of four articles focused on the MOSAiC expedition.

“The really warm summer in the Arctic has really had its impact on the ice,” says Prof Markus Rex, an atmospheric scientist from the Alfred Wegener Institute (AWI). Rex is the leader of MOSAiC, one of the largest Arctic research expeditions ever attempted. (Carbon Brief recently joined the year-long expedition for its first six weeks at sea.)

Rex has spent the months leading up to the expedition closely following Arctic weather reports. The Arctic was hit by higher-than-average temperatures in May and July 2019, which likely worsened the pace of summer sea ice melt, he says.

The extent of Arctic sea ice in September 1979 (dark blue) and September 2019 (light blue). September is typically the month when the Arctic sees its “sea ice summer minimum”. Data source: National Snow and Ice Data Center. Map by Tom Prater for Carbon Brief.

This year’s sea-ice low fits into a picture of recent rapid change. The past 13 years have seen the 13 lowest summer sea ice minimums on record.

With less sea ice surviving from one year to the next, the average age of the ice has also decreased. In the 1980s, the majority of sea ice found in the Arctic was “multi-year ice” – ice that has survived at least one melt season. However, over the past decade, the ice pack has shifted to be majority “first-year ice”, which is typically thinner and more prone to melting in the summer.

Arctic sea ice: 1984-5

Satellites began monitoring Arctic sea ice around the 1980s. At this time, the pole was mostly covered by “multi-year ice” – ice older than one year. This ice is thicker and more stable than young ice.

Each year, sea ice grows in the cold winter months before shrinking back again in summer. This creates the ebb and flow pattern seen in the visualisation.

Arctic sea ice: 2017-18

In the past three decades, the ice pack has shifted to be mostly “first-year ice”, which is less than one year old. First-year ice is more fragile and prone to melting. In the same time period, the total area covered by sea ice has fallen by more than 40%.

Credit: NASA's Scientific Visualization Studio

(A visualisation of sea ice cover and age over the entire time series – 1984-2019 – can be viewed at the bottom of the article.)

The rapid downturn in sea ice over the satellite record has outpaced even the most pessimistic of the projections made by climate models, the mathematical tools that scientists use to make projections about the Earth’s future.

A leading scientific aim of the MOSAiC expedition is to gain a clearer picture of how natural and human-caused influences are driving rapid sea ice loss. The hope is to gain insights which, in time, could improve the models used to make projections about Arctic sea ice.

“There hasn’t been a lot of improvement in how our models have represented declining sea ice over the last couple of decades,” says Dr Matthew Shupe, co-leader of MOSAiC and an Arctic researcher from the University of Colorado, Boulder and the National Oceanic and Atmospheric Administration (NOAA). “So our top level goal is improving models.”

Improving climate models could help to answer questions about future ice decline. One that remains unanswered is when, if at all, the Arctic could see its first “ice-free” summer.

Scientists have various ways of defining what “ice free” actually means, but the most common definition refers to a point at which Arctic sea ice cover at the end of summer falls to below one million square kilometres. At this point, researchers expect the central Arctic Ocean to be completely ice free, with remnants of sea ice persisting along the northern coastlines of Canada, Alaska and Greenland.

The point at which sea ice cover falls to close to zero in the summer will have serious consequences, but, in some ways, could be viewed as a symbolic measure, says Dr Marika Holland, a senior sea ice scientist at the University Corporation for Atmospheric Research (UCAR), who will use MOSAiC data to make projections about the Arctic’s future. She says:

“Reaching an ice-free Arctic summer is just a further exclamation point, emphasising that this is happening and it is dramatic and unprecedented. But from my perspective, the changes are already dramatic and unprecedented – and we can’t lose sight of that.”

Changes in the extent of Arctic sea ice aged less than one year (light blue) to ice aged four years and over (dark blue) over time. Extent is shown for the same week (22-28 October) from 1985-2019. Data source: National Snow and Ice Data Center. Chart by Carbon Brief using Highcharts

Arctic heat

The sharp downturn in sea ice seen in recent decades is closely linked to climate change. The Arctic is one of the most rapidly warming regions on Earth. Average global temperatures have risen by around 1C since the start of the industrial era, but the Arctic has seen around double this amount of warming. In some parts of the Arctic, temperature rise is four times higher than the global average.

Research published in 2016 calculated that for every tonne of CO2 emitted into the atmosphere, summer sea ice cover in the Arctic shrinks by three square metres. (A tonne of CO2 is around the amount emitted by someone travelling on a return economy ticket from London to New York.)

The phenomenon of the Arctic heating up at a faster rate that the rest of the globe is known as “Arctic amplification”. The reasons why Arctic amplification is happening are complex, but research suggests that the phenomenon is closely related to interactions between the atmosphere, sea ice and ocean.

An example of such an interaction occurs when sea ice melts. Climate change brings more heat to the Arctic’s atmosphere and ocean, causing sea ice to melt more rapidly. Sea ice is bright white and, so, reflects away the majority of incoming sunlight. When ice disappears, it uncovers the dark ocean, which absorbs a larger proportion of sunlight. This means that shrinking ice cover causes the Arctic to warm more rapidly, which, in turn, causes more sea ice to disappear.

Illustration of how sunlight interacts with sea ice in comparison to the ocean. Credit: Tom Prater for Carbon Brief

This interaction is known as the “ice-albedo feedback” – or the “albedo effect”. (“Albedo” is a term used to describe the reflectiveness of a surface.) It is one of the most well-known of the feedback loops that impact the rate of Arctic sea ice melt – but there are many others, explains Dr Michel Tsamados, a sea ice researcher from University College London taking part in the MOSAiC expedition. “Some of them are positive and some are negative,” he says.

Positive feedbacks are processes that are self-reinforcing, such as the disappearance of sea ice leading to more warming and, thus, more ice melt. Negative feedbacks, however, are processes that lead to regulation of a change in the system.

For example, in recent years, scientists have observed an increase in the speed at which sea ice grows in the winter. This is partly because “thinner ice can grow much faster than thicker ice”, says Tsamados. “This is a negative feedback – a kind of resilience in the system.”

However, the increase in sea-ice growth observed in winter is not enough to counter the rapid rise in melting seen in the summer months, he adds. “We’re putting out so much CO2 that the Arctic just cannot fight back. Right now, the positive feedbacks are winning against the negative feedbacks – and that means that sea ice is going down the drain.”

Complete picture

Disentangling the influence of both positive and negative feedbacks on Arctic sea ice is a major goal of the MOSAiC expedition. To do this, the researchers are studying every aspect of the Arctic climate system.

The expedition is centred around the Polarstern, a German research ship that has deliberately frozen itself into the sea ice for an entire year. Surrounding the ship is a sprawling ice camp, featuring instruments that are measuring changes to the sea ice, as well as to the atmosphere, ocean and ecosystem.

Dr Matthew Shupe fixes a cable at “Met City” – one faction of MOSAiC’s ice camp. Credit: Daisy Dunne for Carbon Brief

“If you want to understand sea ice, you have to understand the ocean and the atmosphere. You have to look at it as a complete package,” says Dr Jeremy Wilkinson, a sea-ice physicist from the British Antarctic Survey taking part in MOSAiC.

This is because many of the feedback loops that affect sea ice involve changes in the ocean and atmosphere.

For example, MOSAiC scientists studying the ice-albedo feedback will not only need to record changes to ice area and thickness, but also the amount of sunlight penetrating the ice and the amount of heat absorbed by the ocean below the sea ice. To do this, they have set up instruments measuring changes to ice thickness close by to those measuring changes to ocean temperature and incoming sunlight.

An on-the-ground radar measuring changes to ice and snow thickness at the MOSAiC ice camp. Credit: Daisy Dunne for Carbon Brief

“We have spectrometers, which measure visible light. We have some of them looking upward toward the sky and some looking downward to the ice surface – and from the ‘refraction’ we get the albedo,” says Dr Marcel Nicolaus, a sea-ice scientist from MOSAiC who is cruise leader on Polarstern during the first leg of the expedition.

“Refraction” is a term used to describe the bending of light that occurs as it passes from the air into the ice. When light hits the surface, some of it will be refracted or absorbed, while some of it will be reflected back into space. Calculating the portion of light that has been refracted, therefore, gives a picture of the ice’s overall reflectiveness, otherwise known as its albedo.

Understanding the interactions between changes to sunlight, the sea ice and the atmosphere will be key to answering questions about the future of Arctic sea ice, says Shupe. “The way we answer questions about the Arctic’s future is with our models – and we have to have models that reliably represent the essential processes and how they interact.”

Another way that MOSAiC scientists hope to get a better picture of sea ice melt is by studying the small-scale processes that take place in the Arctic. For example, researchers from the atmospheric and sea-ice teams are using specialised instruments to measure the amount of heat escaping from tiny cracks in the sea ice, while the ecosystem team has deployed an underwater camera to record the growth of algae on the underbelly of the sea ice.

The bow of Polarstern seen through the eyes of an autonomous underwater camera from a four-metre depth. Credit: Alfred Wegener Institute

Such small processes underpin the more wide-scale systems that, ultimately, determine sea ice cover, says Shupe.

Gaining data on such small-scale processes could also be key to improving the climate models used to make projections about future sea ice levels, says Dr Thomas Rackow, a climate modeller from AWI who is taking part in MOSAiC. “The idea with MOSAiC is to get a better understanding of small-scale processes that often need to be ‘parameterised’ in the climate models,” he says.

Some processes that impact sea ice take place on scales that are smaller than climate models can capture in their simulations. Scientists instead have to simplify the effect that those processes have on sea ice by using mathematical equations to represent them. This is known as “parameterisation”.

“Melt ponds” are one example of a small-scale process that is not well represented in climate models, says Tsamados. During the summer months, warm air temperatures can cause the sea ice to melt from above, leading to the formation of deep pools of water – known as melt ponds – on top of the ice surface.

Melt pond in the Arctic. Credit: dpa picture alliance / Alamy Stock Photo.

These ponds put pressure on the ice, increasing the chances of collapse. They also change the ice’s reflectiveness – or “albedo” – causing it to absorb more or less heat. Despite these impacts, some climate models do not include melt ponds in their simulations, or else assume that all melt ponds look and behave in the same way.

One reason that climate models do not simulate small-scale processes well is because there is relatively little field data available that detail how these processes work. Or that the available data only runs the course of a few weeks – the usual amount of time for an Arctic field study, Shupe says. By spending an entire year drifting in the sea ice, the MOSAiC team aim to collect more comprehensive data, which could, in time, be used to plug the gaps in climate models, he adds.

Setting a date

Improving the ability of climate models to simulate the Arctic region will be a key step in better pinning down the date at which the Arctic will see its first ice-free summer, Rackow says. “There’s still a big range and it depends on the model that you’re looking at. But, basically, what all the models show is that, at some point, summer sea ice will be lost.”

The date at which the Arctic will have its first ice-free summer has proved tricky to forecast. Different climate models come up with a wide range of possible dates, spanning 2005 to after 2100. The majority of climate models, however, suggest that it is likely to happen sometime around the middle of the century.

Even though improving climate models could be key to coming up with a more refined estimate, there are several factors that complicate matters further.

The first is that the speed at which humans produce greenhouse gas emissions in the coming decades will play a large role in determining how quickly Arctic sea ice disappears.

A study published in 2016 found that, if humans make very little effort to cut global emissions, the Arctic could see its first ice-free summer as early as 2032. (This finding assumes the world follows a scenario of very high emissions known as “RCP8.5”.)

However, limiting global warming to 1.5C – the aspirational temperature target set by countries under the Paris Agreement – could greatly reduce the chances of the Arctic becoming ice free in the summer.

The probability of the Arctic seeing its first ice-free summer from 2020-2100 under a range of future scenarios, including where global temperature rise is limited to 1.5C (yellow), 1.5C with “temperature overshoot” (blue) and 2C (light blue). Scenarios where these temperature targets are exceeded are also shown. This includes a scenario of moderately high emissions (RCP4.5; dark blue) and a scenario of very high emissions (RCP8.5; red). Adapted from Jahn et al. 2018.

A study published in 2018 found that, if global temperatures are limited to 1.5C, the Arctic is “very unlikely” to see its first ice-free summer before 2065. After this point, the chances of the Arctic seeing its first ice-free summer increase to around one-in-five for any given year.

In comparison, if temperatures rise by 2C – the upper limit set by the Paris Agreement – the Arctic has a one-in-five chance of seeing its first ice-free summer in 2035, according to the study. The chances of an ice-free summer in any given year rise to one-in-two by 2045.

“I was surprised that half a degree of warming would make such a big difference,” study lead author Dr Alexandra Jahn, an assistant professor in atmospheric and oceanic sciences at the University of Colorado, Boulder, told Carbon Brief in 2018.

The second factor that complicates pinning down a date for the first ice-free summer is “natural variability” – a term used to describe the influence of year-to-year natural events and processes that affect the sea ice.

MOSAiC scientists start to move equipment as an Arctic storm descends. Credit: Esther Horvath/Alfred Wegener Institute

Arctic storms are one type of natural event that can affect sea ice. Unlike mid-latitude cyclones, Arctic storms do not typically carry a lot of snow and rain. They can, however, bring extremely strong winds, which can rip through the sea ice, causing it to break apart, explains Dr Ola Persson, a polar meteorologist from the National Oceanic and Atmospheric Administration (NOAA) taking part in MOSAiC. He says:

“What people have been noticing in the past few years is that when we have a really big Arctic cyclone, the sea ice disappears.”

In 2012, Arctic summer sea ice reached its lowest level on record – in part due to a large storm hitting the ice in August.

A landmark report on oceans and ice published this year by the Intergovernmental Panel on Climate Change (IPCC) found that up to half of the observed decline in summer sea ice could be down to natural variability in the Arctic climate.

“There are challenges for pinning down a date for the first ice-free summer just because there is internal natural variability in the system – that means that will always be uncertainty,” says Holland.

A study published in 2016 calculated that natural variability in the Arctic system amounted to around two decades of uncertainty. This means that any ice-free summer forecast may need to have a 20-year window, just to account for the influence of natural events and processes.

The field measurements taken during MOSAiC are likely to improve the ability of climate models to forecast changes in the Arctic – but this could take some time, says Prof Jari Haapala, a MOSAiC scientist who is head of the Marine Research Unit at the Finnish Meteorological Institute.

“If I’m being realistic, it will take at least five years for the new results from MOSAiC to be implemented in the climate models. It could probably take longer.”

This is because all the field results from MOSAiC will first need to be analysed, then published in peer-reviewed scientific journals – and then relayed to the climate modelling community, says Haapala.

A major concern is that Arctic sea ice is shifting so rapidly that climate modellers may not be able to keep up with the pace of change, says Rackow:

"We’re running out of time. If an ice-free summer does occur at the earliest forecasted date – around 2035 – then that’s not much time left. It could be that reality overtakes our ability to make predictions.”

Ice-free implications

The point at which the Arctic sees its first ice-free summer will have repercussions both in the polar region and beyond.

One industry that has followed sea-ice forecasting research with keen interest is commercial shipping. Ever since humans first started navigating the seas, international traders have sought the most cost-effective route between the world’s ports. For many, the shortest route between the Atlantic and Pacific Oceans would be through the Arctic – but the presence of thick sea ice has prevented passage for all but the hardiest ships.

The disappearance of sea ice in the summer would allow ships to find a new, faster route between the Atlantic and Pacific Oceans. A study published in 2016 found that routes across the Arctic could become available for standard open-water vessels by the middle of the century. “I think the Arctic will look very different [at that time] and will have a lot more activities and resources being exploited. That’s probably coming,” says Rackow.

The opening up of new shipping routes could bring increased threats to the Arctic’s unique wildlife. A study published in 2018 found that the expansion of commercial shipping poses a significant threat to a wide range of Arctic marine mammals, including narwhals, bowhead whales, belugas and polar bears.

Narwhal whale in Arctic Bay, Nunavut, Canada. Credit: Todd Mintz / Alamy Stock Photo.

Animals in the Arctic are likely to face further threats as sea ice disappears, says Dr Allison Fong, co-coordinator of the ecosystems research team for MOSAiC from AWI. She tells Carbon Brief:

“Without the persistence of sea ice through the summer, there could be really strong implications for biota [wildlife] that utilise ice as a habitat. Ice is also an environment that carries organisms from other parts of the Arctic to the central Arctic – so this could have implications for what seeding populations are there during the growing season.”

These changes could impact every level of the Arctic ecosystem, says Fong, from the plant algae growing on the underside of the sea ice to the polar bear, the region’s top predator.

A study published in 2018 found that sea ice decline could be making it harder for polar bears to find food. The preferred prey of polar bears is the ringed seal, which the bears hunt from the ice surface. The study tracked a group of female bears living in the Beaufort Sea in 2014-16 and found that, on average, bears were travelling further to find food than in previous years – and expending more energy in the process.

Though a clear link has yet to be established, it is possible that the reason bears are travelling longer distances is because declining sea ice is leaving them with fewer places to hunt seals, Dr Anthony Pagano, a research follow at the Institute for Conservation Research at San Diego Zoo, told Carbon Brief in 2018:

A mother polar bear and her cub in the Central Arctic Ocean. Credit: Daisy Dunne for Carbon Brief

“The concern is that as the ice breaks up earlier each year, the bears will be impacted in three ways: they’ll be less successful at catching seals because they’re being displaced from their primary foraging habitat earlier; they’re putting on less weight than they would have done historically; and then they’re also moving greater distances. If that trend continues, we would expect continued declines in reproductive success.”

A second study published this year found that polar bears may tune their foraging behaviour to be in line with the pattern of ice growth and retreat seen each year. This “implies that even minor advances in the timing of [ice] break‐up may have detrimental effects on foraging opportunities, body condition, and subsequent reproduction and survival,” the authors say.

Changes to ice conditions affect indigenous human populations, too, says Holland. “It also has implications for people that use the ice for travelling or for hunting because young ice is not as stable or as safe,” she says.

People living in lower-latitude regions could also be affected, though less directly, by sea ice decline. A growing field of research suggests that changes to sea ice could be affecting weather elsewhere, particularly in mid-latitude regions.

Inupiaq hunters look out over the Chukchi Sea, Barrow, Alaska. Credit: Design Pics Inc / Alamy Stock Photo.

“What happens in the Arctic doesn’t stay in the Arctic,” Tsamados says. “The general circulation of the ocean, weather patterns in the lower latitude – these are things that are intimately linked with the Arctic.”

Scientists have noted that the recent rapid changes in the Arctic seem to have coincided with a period of more frequent extreme weather events across the northern hemisphere. Such events include severe winters in the US, Canada and Europe, as well as heatwaves and droughts.

Some scientists believe that the two phenomena are linked. Exactly how changes in the Arctic could be driving increases in extreme weather events in the mid-latitudes is still up for debate. (Carbon Brief this year published a detailed explainer examining the proposed mechanisms.)

Research published in 2014 found that Arctic sea ice decline could have caused a doubling in the likelihood of extreme cold winters in Eurasia. A later study found that Arctic warming could also be linked to more intense heatwaves in the northern hemisphere.

However, a study published this year found that Arctic sea ice changes could have a “minimal influence” on severe winters in the mid-latitudes.

Using climate models, the researchers found that declines in sea ice do not always precede cold winters. In their model simulations, the researchers instead observed that the two events often happened at the same time – suggesting that they may have a common cause, Dr Russell Blackport, a research fellow at the University of Exeter, said at the time of the paper’s release. “The correlation between reduced sea ice and cold winters does not mean one is causing the other.”

More research will be needed to understand the true impacts of dramatic Arctic decline – both in the region and beyond, says Fong:

“We need a lot of data, over many years – successive years – to actually identify what the impacts of [sea ice decline] will be. These are concentrations of CO2 that have never been seen in modern history. It’s clear that there will be implications but, what those implications are, it’s hard to say.”

Daisy Dunne was one of five journalists selected to report on MOSAiC. Her costs once leaving Tromso were covered by the Alfred Wegener Institute, which organised the expedition.

Satellite imagery credit: NASA's Scientific Visualization Studio