Arctic ice cap slides into the ocean

Arctic ice cap slides into the ocean

Satellite images have revealed that a remote Arctic ice cap has thinned by more than 50 metres since 2012 – about one sixth of its original thickness – and that it is now flowing 25 times faster.

Heavily crevassed terminus of Kapp Mohn outlet glacier, Austfonna, in May 2013, after 25-fold increase in flow speed (Dunse et al., The Cryosphere Discussions, 2014). Credit: Thorben Dunse, University of Oslo

CPOM scientists combined observations from eight satellite missions, including Sentinel-1A and CryoSat, with results from regional climate models, to unravel the story of ice decline.

The findings show that over the last two decades, ice loss from the south-east region of Austfonna, located in the Svalbard archipelago, has increased significantly. In this time, ice flow has accelerated to speeds of several kilometres per year, and ice thinning has spread more than 50km inland – to within 10km of the summit.

Rate of ice cap elevation change between 2010 and 2014 observed CryoSat, overlaid onto an image acquired by the Sentinel-1A satellite. Red regions show where the ice surface has lowered due to ice loss. Credit: CPOM/GRL

“These results provide a clear example of just how quickly ice caps can evolve, and highlight the challenges associated with making projections of their future contribution to sea level rise,” said the study’s lead author Dr Mal McMillan.

The study, published in Geophysical Research Letters and reported online today by the European Space Agency (ESA), is the first to make use of measurements from ESA’s latest Earth observation satellite, Sentinel-1A.

Sentinel-1A, the first satellite developed for Europe’s Copernicus programme, was launched in April last year, while CryoSat has been in orbit since 2010.

Dr McMillan said: “New satellites, such as the Sentinel-1A and CryoSat missions, are essential for enabling us to systematically monitor ice caps and ice sheets, and to better understand these remote polar environments.”

Melting ice caps and glaciers are responsible for about a third of recent global sea level rise. Although scientists predict that they will continue to lose ice in the future, determining the exact amount is difficult, due both to a lack of observations and the complex nature of their interaction with the surrounding climate.

“Glacier surges, similar to what we have observed, are a well-known phenomenon,” said CPOM Director Andy Shepherd.

“However, what we see here is unusual because it has developed over such a long period of time, and appears to have started when ice began to thin and accelerate at the coast.”

There is evidence that the surrounding ocean temperature has increased in recent years, which may have been the original trigger for the ice cap thinning.

“Whether or not the warmer ocean water and ice cap behaviour are directly linked remains an unanswered question. Feeding the results into existing ice flow models may help us to shed light on the cause, and also improve predictions of global ice loss and sea level rise in the future,” said Professor Shepherd.

Long-term observations by satellites are the key to monitoring such climate-related phenomena in the years and decades to come.

The paper, Rapid dynamic activation of a marine-based Arctic ice cap, was published online by Geophysical Research Letters as an Early Access article on 23 December 2014.

Migrating supraglacial lakes could trigger future Greenland ice loss

Supraglacial lakes on the Greenland ice sheet can be seen as dark blue specks in the centre and to the right of this satellite image. Credit: USGS/NASA Landsat

The finding follows a new study, published in Nature Climate Change, in which the future distribution of lakes that form on the ice sheet surface from melted snow and ice ,called supraglacial lakes, have been simulated for the first time.

Previously, the impact of supraglacial lakes on Greenland ice loss had been assumed to be small, but the new research has shown that they will migrate farther inland over the next half century, potentially altering the ice sheet flow in dramatic ways.

Dr Amber Leeson, who led the study, said: “Supraglacial lakes can increase the speed at which the ice sheet melts and flows, and our research shows that by 2060 the area of Greenland covered by them will double.”

Supraglacial lakes are darker than ice, so they absorb more of the Sun’s heat, which leads to increased melting. When the lakes reach a critical size, they drain through ice fractures, allowing water to reach the ice sheet base which causes it to slide more quickly into the oceans. These changes can also trigger further melting.

Dr Leeson explained: “When you pour pancake batter into a pan, if it rushes quickly to the edges of the pan, you end up with a thin pancake. It’s similar to what happens with ice sheets: the faster it flows, the thinner it will be.

“When the ice sheet is thinner, it is at a slightly lower elevation and at the mercy of warmer air temperatures than it would have been if it were thicker, increasing the size of the melt zone around the edge of the ice sheet.”

Until now, supraglacial lakes have formed at low elevations around the coastline of Greenland, in a band that is roughly 100km wide. At higher elevations, today’s climate is just too cold for lakes to form.

In the study, the scientists used observations of the ice sheet from the Environmental Remote Sensing satellites operated by the European Space Agency and estimates of future ice melting drawn from a climate model to drive simulations of how meltwater will flow and pool on the ice surface to form supraglacial lakes.

Since the 1970s, the band in which supraglacial lakes can form on Greenland has crept 56km further inland. From the results of the new study, the researchers predict that, as Arctic temperatures rise, supraglacial lakes will spread much farther inland – up to 110 km by 2060 – doubling the area of Greenland that they cover today.

Dr Leeson said: “The location of these new lakes is important; they will be far enough inland so that water leaking from them will not drain into the oceans as effectively as it does from today’s lakes that are near to the coastline and connected to a network of drainage channels.”

“In contrast, water draining from lakes farther inland could lubricate the ice more effectively, causing it to speed up.”

Ice losses from Greenland had been expected to contribute 22cm to global sea-level rise by 2100.  However, the models used to make this projection did not account for changes in the distribution of supraglacial lakes, which Dr Leeson’s study reveals will be considerable.

If new lakes trigger further increases in ice melting and flow, then Greenland’s future ice losses and its contribution to global sea-level rise have been underestimated.

CPOM Director Andy Shepherd, who co-authored the study, said: “Because ice losses from Greenland are a key signal of global climate change, it’s important that we consider all factors that could affect the rate at which it will lose ice as climate warms.

“Our findings will help to improve the next generation of ice sheet models, so that we can have greater confidence in projections of future sea-level rise. In the meantime, we will continue to monitor changes in the ice sheet losses using satellite measurements.”

The paper, Supraglacial lakes on the Greenland ice sheet advance inland under warming climate, was published in Nature Climate Change on 15 December 2014.

CryoSat extends its reach on the Arctic

Five years’ ice thickness change. Credit: ESA/CPOM

CryoSat has delivered this year’s map of autumn sea-ice thickness in the Arctic, revealing a small decrease in ice volume. In a new phase for ESA’s ice mission, the measurements can now also be used to help vessels navigate through the north coastal waters of Alaska, for example.

Measurements made during October and November show that the volume of Arctic sea ice now stands at about 10,200 cubic km – a small drop compared to last year’s 10,900 cubic km.

The volume is the second-highest since measurements began in 2010, and the five-year average is relatively stable. This, however, does not necessarily indicate a turn in the long-term downward trend.

“We must to take care when computing long-term trends as this CryoSat assessment is short when compared to other climate records,” said CPOM Director Andy Shepherd.

“For reliable predictions, we should try other approaches, like considering what is forcing the changes, incorporating the CryoSat data into predictive models based on solid physics, or simply waiting until more measurements have been collected.”

CryoSat was designed to measure sea-ice thickness across the entire Arctic Ocean, enabling scientists to monitor accurately the overall change in volume.

While the amount of ice normally fluctuates depending on the season, longer-term satellite records show a constant downward trend in ice extent during all seasons, in particular in summer, with a minimum occurring in the autumn of 2012.

Establishing whether the ice volume is following a similar trend is one of CryoSat’s key mission objectives.

“October is interesting because it is the first month we get data directly following the sea-ice minimum in September, so that’s where we see the largest interannual variability in our volume estimates,” said Rachel Tilling, who is working on the CryoSat measurements as part of her PhD studies.

Launched in 2010, CryoSat has long surpassed its planned three-year life. At the mission’s recent mid-term review, it was further extended until February 2017.

Ice thickness for operational applications. Credit: ESA/CPOM

Tommaso Parrinello, ESA’s CryoSat Mission Manager, said CryoSat has already achieved outstanding results, both within its original mission objectives and for unexpected applications.

“Looking ahead, we are working hard to prototype new operational capabilities so that the measurements can be used for routine assessments in climate science and for services affected by Arctic sea ice.”

To test this, scientists have produced an assessment of sea-ice thickness north of Alaska and eastern Russia with data acquired over the last month. Products like this could prove useful for maritime services, such as shipping and exploration.

Arctic sea ice: a cool start to spring

CPOM’s Danny Feltham describes the current state of the Arctic sea ice and explains the uncertainties on Reading University’s Weather and Climate blog.

Arctic sea ice. Credit:Tom Armitage

CryoSat beams down today’s Arctic sea ice

Having just celebrated its milestone fifth birthday, CryoSat has become the first mission to provide information on Arctic sea ice thickness in real-time as an aid to maritime activities.

The European Space Agency’s (ESA) CryoSat satellite has been measuring the thickness of polar ice to the nearest centimetre since its launch in 2010.  It is already the first mission to deliver complete maps of Arctic sea ice thickness – a key indicator of global climate change and of the state of the Arctic itself.  Now, thanks to specialist data processing at CPOM, CryoSat is producing the first rapid measurements of Arctic sea ice thickness.

Arctic sea ice thickness in April 2015, as recorded by CryoSat

With measurements becoming available via a new website within two days of the satellite passing over the ice, the results will help people using the Arctic to plan and manage their activities, in addition to improving scientific understanding of the Polar Regions.

CPOM researcher Rachel Tilling explains: “We’ve already found that, although Arctic sea ice set a record this year for its lowest ever winter extent, it was about 25 cm thicker, on average, than in 2013, when CryoSat recorded its lowest winter volume.”

Although there is more ice overall than there was in 2013, in some places the sea ice has thinned progressively; for example north of Svalbard the winter sea ice is now only 1 metre thick – half what it was in 2011 when CryoSat made its first measurements of the area.

The latest measurements also show that sea ice around Svalbard, 1,300 miles from the North Pole, is today only a metre thick – approximately half what it was in the winter of 2011 just after CryoSat was launched.  Professor Andy Shepherd, CPOM Director and principal scientific advisor to the CryoSat mission, added: “the thinner ice around Svalbard coincides with a warming of the surrounding Barents Sea.

“We’ve already seen the impact of this change in ocean conditions on Svalbard’s Austfonna ice cap, where glaciers have speeded up at unprecedented rates, and the rapid retreat of sea ice in this sector of the Arctic is almost certainly down to the same thing.”

As well as helping scientists to understand the rapidly changing Arctic environment, the real time CryoSat data will be a vital resource for maritime activities affected by sea ice, such as shipping, tourism, Arctic exploration, and of course search and rescue.

With economic growth in the Arctic estimated to be worth $100bn over the next two decades, timely and routine information on sea ice thickness will help to ensure that users of the Arctic can plan and carry out their operations safely and with care.

Professor Shepherd highlighted: “This new capability goes far beyond CryoSat’s original purpose, which was to collect measurements for scientific research; the mission is now an essential tool for a wide range of services operating in areas of the planet where sea ice forms.”

CryoSat’s real-time measurements were first trialled in Spring 2014 to guide a scientific experiment north of Greenland led by CPOM, and the service will be tested next week when the Norwegian Polar Institute’s Young Sea Ice mission carries out experiments in the sea ice pack north of Svalbard.

Speaking about CryoSat’s achievements, ESA mission manager Tommaso Parrinello said: “After five years of exploitation, CryoSat has provided important answers, but has also enlarged our lack of knowledge on several fundamental scientific questions.

“Similarly, CryoSat has shown the importance of its measurements for current and future operational and forecasting services on all Arctic latitudes, paving the way to the development of similar missions in future.”

Latest CPOM sea ice report

17 April 2015

Although Arctic sea ice set a record this year for its lowest ever winter extent, it was on average 25cm thicker than in 2013 when CryoSat recorded its lowest winter volume.

The latest measurements also show that sea ice around Svalbard, 1300 miles from the North Pole, is today only a metre thick – approximately half what it was in the winter of 2011 just after CryoSat was launched. The thinner ice around Svalbard coincides with a warming of the surrounding Barents Sea.

We’ve already seen the impact of this change in ocean conditions on the Svalbard’s Austfonna ice cap where glaciers have speeded up at an unprecidented rate, and the rapid retreat of sea ice in this sector of the Arctic is almost certainly down to the same thing.

See the full results on the CryoSat Operational Monitoring Website.

Pine Island Glacier on Sentinel-1’s radar

This image combining two scans by Sentinel-1A’s radar shows that parts of the Pine Island glacier flowed about 100 m (in pink) between 3 March and 15 March 2015. Light blue represents stable ice on either side of the stream.

Pine Island Glacier on Sentinel-1A’s radar. Credit: Copernicus data (2015)/ESA/A.Hogg/CPOM

Pine Island is the largest glacier in the West Antarctic Ice Sheet and one of the fastest ice streams on the continent, with an average of over 4 km per year. About a tenth of the ice sheet drains out to the sea by way of this glacier.

With its all-weather, day and night radar vision, the Sentinel-1 mission is an important tool for monitoring polar regions and the effects that climate change has on ice.  You can see more images from Sentinel-1A on ESA’s website.