The largest and most ambitious Polar research expedition in history returned to Germany from the Arctic on Monday with stark warnings of dramatic ice loss.
After a year spent anchored to packed ice drifting around the North Pole, scientists aboard the Polarstern icebreaker docked in Bremerhaven, bringing back valuable data from what's been called "the epicentre of global warming".
The 140 million euro MOSAiC mission (Multidisciplinary drifting Observatory for the Study of Arctic Climate), led by the Alfred Wegener Institute, involved 600 researchers from 20 countries.
Through polar nights of 24-hour blackness and polar days when the sun did not set, the scientists carried out experiments on the surrounding ecosystem in a quest to assess the impact of climate change and the loss of polar ice.
Thousands of samples of snow, ice, water and air were collected in a haul that expedition leader Professor Markus Rex told German media would keep "generations" of future scientists busy.
His first word on the landmark voyage, however, was to sound the alarm on vanishing ice above Greenland, a situation that allowed the ship to make an unplanned detour to the North Pole itself - and in record time.
"The ice at the North Pole had completely melted; there were areas of open water until just before the pole," Rex told the German press agency DPA. "We watched the ice die."
'New climate regime'
While the South Pole lies on the continental land mass that is Antarctica, the North Pole sits squarely in the Arctic Ocean, a delicate landscape of snow and ice that has been undergoing massive changes in recent years.
Arctic sea ice shrinks and regrows according to the seasons. The Arctic Ocean and neighbouring seas are completely covered in ice during the winter months. This thins and shrinks towards the end of the spring, before reaching its lowest levels in late September.
New research published in the journal Nature Climate Change warns the region is already shifting to an "entirely new climate regime", while the latest figures from the US National Snow and Ice Data Centre show that Arctic sea ice has shrunk to its second-lowest level since satellite records began 42 years ago.
View from orbit
Satellite images help to track the changes taking place in the Arctic, a vast and remote region where the extreme cold and long periods of darkness make conditions difficult on the ground.
For the MOSAiC mission these images were crucial, with satellites run by Europe, Canada, Germany and Japan all providing the team aboard the Polarstern with much-needed visuals of the ever-changing icescape surrounding them.
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The European Space Agency (ESA), which offered a set of eyes from orbit via its CryoSat environmental research satellite, also took part in the terrestrial mission, carrying out its own experiments on the sea ice.
"We felt that one of the best ways we could contribute to MOSAiC was to send some ground instruments that could replicate something we would expect from a satellite," explains Tnia Casal, ESA's scientific campaign coordinator.
"This was a unique opportunity to obtain sea ice measurements throughout a whole year and at a much larger scale."
Readings taken from four ESA instruments, Casal says, will help construct a better understanding of the constantly evolving energy flows between the Arctic's ice, ocean and atmosphere over the seasons - and how they're responding to climate change.
Those readings will be matched with data from CryoSat - launched in 2010 with the specific purpose of measuring ice thickness - and other satellites including the EU's Sentinel family, with the aim of developing more accurate climate modelling scenarios for the future.
This data is key in ensuring that next-generation satellite missions, such as Europe's 300-million euro CRISTAL ice-monitoring satellite - set to launch in 2027 - are able to send reliable information back to Earth, Casal says.
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"Both of the poles are key indicator regions for climate change - and they're telling us that something needs to be done," she adds. "It's clear that things are changing and they're changing at an incredible pace."
Now begins the job of analysing the samples and data that have resulted from the Polarstern's year watching the Arctic freeze and then melt.
It's a monumental task that is expected to take climate research to a new level.