Nav: Home

Weather anomalies accelerate the melting of sea ice

January 16, 2018

In the winter of 2015/16, something happened that had never before been seen on this scale: at the end of December, temperatures rose above zero degrees Celsius for several days in parts of the Arctic. Temperatures of up to eight degrees were registered north of Svalbard. Temperatures this high have not been recorded in the winter half of the year since the beginning of systematic measurements at the end of the 1970s. As a result of this unusual warmth, the sea ice began to melt.

"We heard about this from the media," says Heini Wernli, Professor of Atmospheric Dynamics at ETH Zurich. The news aroused his scientific curiosity, and a team led by his then doctoral student Hanin Binder investigated the issue. In November 2017, they published their analysis of this exceptional event in the journal Geophysical Research Letters.

In it, the researchers show how these unusual temperatures arose: three different air currents met over the North Sea between Scotland and southern Norway, carrying warm air northwards at high speed as though on a "highway".

One air current originated in the Sahara and brought near-surface warm air with it. To begin with, temperature of this air was about 20 degrees Celsius. While it cooled off on its way to the Arctic, it was still above zero when it arrived. "It's extremely rare for warm, near-surface subtropical air to be transported as far as the Arctic," says Binder.

The second air current originated in the Arctic itself, a fact that astonished the scientists. To begin with, this air was very cold. However, the air mass - which also lay close to the ground - moved towards the south along a curved path and, while above the Atlantic, was warmed significantly by the heatflux from the ocean before joining the subtropical air current.

The third warm air current started as a cold air mass in the upper troposphere, from an altitude above 5 kilometres. These air masses were carried from west to east and descended in a stationary high-pressure area over Scandinavia. Compression thereby warmed the originally cold air, before it entered the "highway to the Arctic".

Poleward warm air transport

This highway of air currents was made possible by a particular constellation of pressure systems over northern Europe. During the period in question, intense low-pressure systems developed over Iceland while an extremely stable high-pressure area formed over Scandinavia. This created a kind of funnel above the North Sea, between Scotland and southern Norway, which channelled the various air currents and steered them northwards to the Arctic.

This highway lasted approximately a week. The pressure systems then decayed and the Arctic returned to its typical frozen winter state. However, the warm period sufficed to reduce the thickness of the sea ice in parts of the Arctic by 30 centimetres - during a period in which ice usually becomes thicker and more widespread.

"These weather conditions and their effect on the sea ice were really exceptional," says Binder. The researchers were not able to identify a direct link to global warming. "We only carried out an analysis of a single event; we didn't research the long-term climate aspects" emphasises Binder.

High-pressure systems cause sea ice to melt

However, the melting of Arctic sea ice during summer is a different story. The long-term trend is clear: the minimum extent and thickness of the sea ice in late summer has been shrinking continually since the end of the 1970s. Sea ice melted particularly severely in 2007 and 2012 - a fact which climate researchers have thus far been unable to fully explain. Along with Lukas Papritz from the University of Bergen, Wernli investigated the causes of these outliers. Their study has just been published in the journal Nature Geoscience.

According to their research, the severe melting in the aforementioned years was caused by stable high-pressure systems that formed repeatedly throughout the summer months. Under these cloud-free weather conditions, the high level of direct sunlight - the sun shines 24 hours a day at this time of year - particularly intensified the melting of the sea ice.

Areas of low pressure "inject" air masses into the Arctic

These high-pressure systems developed through an influx of air from temperate latitudes. Low-pressure systems in the North Atlantic and North Pacific areas, for example, "inject" air masses into the Arctic at a height of about eight kilometres. This raised the height of the tropopause, the boundary between the troposphere and the stratosphere, in the region of the "injections". As a result, surface air pressure below rose and a high-pressure system was established. While it dissipated again around ten days later, an unusually high amount of sea ice melted in the interim, and the remaining ice thinned.

The climate scientists' investigation demonstrated that in the summers of 2007 and 2012, during which these high-pressure situations occurred particularly frequently, they led to cloud-free conditions every third day. The high level of solar radiation intensified and accelerated the melting of the sea ice. "The level of solar radiation is the main factor in the melting of the ice in summer. Unlike with the winter anomaly, the "injected" air at about 8 kilometre altitude from the south is not warm - with minus 60 degrees it's ice-cold," says Wernli.

"The air temperature therefore has very little effect on the ice." Furthermore, the northward transport of warm, humid air masses at the edge of the high-pressure systems reduces (heat) emission, which further intensifies melting.

Their analysis has allowed the researchers to understand the meteorological processes leading to significant variations in summertime ice melt for the first time. "Our results underline the fundamental role that weather systems in temperate latitudes play in episodes of particularly intense ice melt in the Arctic," says the ETH professor.

ETH Zurich

Related Sea Ice Articles:

Earth's glacial cycles enhanced by Antarctic sea-ice
A 784,000 year climate simulation suggests that Southern Ocean sea ice significantly reduces deep ocean ventilation to the atmosphere during glacial periods by reducing both atmospheric exposure of surface waters and vertical mixing of deep ocean waters; in a global carbon cycle model, these effects led to a 40 ppm reduction in atmospheric CO2 during glacial periods relative to pre-industrial level, suggesting how sea ice can drive carbon sequestration early within a glacial cycle.
Arctic sea ice can't 'bounce back'
Arctic sea ice cannot 'quickly bounce back' if climate change causes it to melt, new research suggests.
Cracks in Arctic sea ice turn low clouds on and off
The prevailing view has been that more leads are associated with more low-level clouds during winter.
Evidence: Antarctica's thinning ice shelves causing more ice to move from land into sea
New study provides the first evidence that thinning ice shelves around Antarctica are causing more ice to move from the land into the sea.
Low sea-ice cover in the Arctic
The sea-ice extent in the Arctic is nearing its annual minimum at the end of the melt season in September.
Study shows algae thrive under Greenland sea ice
Microscopic marine plants flourish beneath the ice that covers the Greenland Sea, according to a new study in the Journal of Geophysical Research: Oceans.
ICESat-2 reveals profile of ice sheets, sea ice, forests
With each pass of the ICESat-2 satellite, the mission is adding to datasets tracking Earth's rapidly changing ice.
Arctic cyclone limits the time-scale of precise sea-ice prediction in Northern Sea Route?
Climate change has accelerated sea-ice retreat in the Arctic Ocean, leading to new opportunities for summer commercial maritime navigation along the Northern Sea Route.
Ocean waves following sea ice loss trigger Antarctic ice shelf collapse
Storm-driven ocean swells have triggered the catastrophic disintegration of Antarctic ice shelves in recent decades, according to new research published in Nature today.
New technique more accurately reflects ponds on Arctic sea ice
This one simple mathematical trick can accurately predict the shape and melting effects of ponds on Arctic sea ice, according to new research by UChicago scientists.
More Sea Ice News and Sea Ice Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

TED Radio Wow-er
School's out, but many kids–and their parents–are still stuck at home. Let's keep learning together. Special guest Guy Raz joins Manoush for an hour packed with TED science lessons for everyone.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.