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Arctic could be free of sea ice by 2035, warns British Antarctic Survey




The Arctic could be free of sea ice by 2035, according to a new study involving Cambridge-based British Antarctic Survey.

If the modelling proves to be accurate, it could have implications for the global climate, ecosystems and human activities.

A polar bear and a melt pond
A polar bear and a melt pond

Unlike glaciers and icebergs, which originate on land then float on the ocean, sea ice is frozen ocean water. It forms and melts in the ocean, and therefore does not directly impact on sea levels. In spring and early summer, shallow pools of water –known as melt ponds – form on the surface of sea ice.

While the white surface of sea ice reflects about 80 per cent of the sunlight hitting it, the darker melt ponds means about 90 per cent of the sunlight is absorbed by the ocean – a process known as the albedo effect.

An international team of researchers used the Met Office’s Hadley Centre climate model to compare current sea ice conditions with those during the last interglacial warm period, around 127,000 years ago.

High temperatures in the Arctic during the interglacial have been puzzling scientists for centuries. Using the model, the research team concluded that the impact of intense springtime sunshine created many melt ponds, which played a key role in the melting of sea ice.

A simulation using the same model indicates the Arctic may become free of sea ice by 2035.

Polar bears on ice
Polar bears on ice

Joint lead author Dr Maria Vittoria Guarino, Earth system modeller at the British Antarctic Survey , says: “Unravelling this mystery was technically and scientifically challenging. For the first time, we can begin to see how the Arctic became sea ice-free during the last interglacial.

“The advances made in climate modelling means that we can create a more accurate simulation of the Earth’s past climate which, in turn, gives us greater confidence in model predictions for the future.”

Dr Louise Sime, the group head of the palaeoclimate group and joint lead author at BAS , adds: “We know the Arctic is undergoing significant changes as our planet warms. By understanding what happened during Earth’s last warm period we are in a better position to understand what will happen in the future. The prospect of loss of sea-ice by 2035 should really be focussing all our minds on achieving a low-carbon world as soon as humanly feasible.”

Dr David Schroeder, from the University of Reading, who co-led the implementation of the melt pond scheme in the climate model, says: “This shows just how important sea-ice processes like melt ponds are in the Arctic, and why it is crucial that they are incorporated into climate models.”

Sea ice is important to the communities living in the region, and is vital for species such as polar bears. By regulating the exchange of heat between the ocean and the atmosphere, it also influences global climate.

If warming temperatures melt sea ice over time, its ability to reflect sunlight will be diminished, more solar energy will be absorbed at the surface and temperatures will rise further. This will create a cycle of warming and melting in summer months.

A polar bear on Arctic ice
A polar bear on Arctic ice

Sea ice also influences the ocean’s global ‘conveyor belt’. When it forms, the ocean water beneath becomes more salty and denser than the surrounding ocean. As saltier water sinks and moves along the bottom of the ocean bottom, so warm water from mid-depth to the surface travels from the equator toward the poles.

Changes to the volume of sea ice will therefore affect normal ocean circulation, and have a further impact on global climate.

The study, published in Nature Climate Change, comes after the National Snow and Ice Data Center reported that Arctic Ocean ice cover reached a new low for the time of year on July 15. It found sea ice was disappearing at a rate of more than 56,400 square miles a day in July – well below the usual rate of 33,000 square miles. While in the 1980s, sea ice covered an average of about3.8 million square miles – about the same size as the United States – this July it extended to just 2.8 million square miles, less than the size of Australia.

Some scientists predict an all-time low may be reached in September, when sea ice is typically at its minimum.

The study, published in Nature Climate Change, was funded by NERC and was part of the TiPES project, which has received funding from the European Union’s Horizon 2020 research and innovation programme.

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