Endurance swimmer Lewis Pugh has completed the most challenging swim of his career in Greenland to highlight the impacts of the climate crisis.

Mr Pugh, who has swum in the Arctic, Antarctic and up the English Channel to push for action to protect the environment, undertook the 4.8-mile (7.8km) swim in the Ilulissat Icefjord in 14 sessions over 12 days.

Swimming in waters fed by the world’s fastest moving glacier, the UN patron of the oceans had to brave water temperatures between 0C and 3C (32F-37.4F) as he became the first person to undertake a multi-day swim in the polar regions.

Mr Pugh took the icy plunge to highlight how human-driven global warming is melting the ice caps and glaciers, pushing up sea levels and threatening coastal communities, ahead of UN climate talks in November in Glasgow.

He is also calling for 30% of the world’s oceans to be protected by 2030, to help tackle the climate crisis and make the seas more resilient to global warming.

He said: “This was an extremely challenging swim. Not only because of the cold, and not just because I had to swim in freezing water day after day, without a chance to let my body recover, but because the conditions were also very treacherous.”

A number of large, grounded icebergs stemming the flow of ice into the mouth of the fjord came apart during the swim, causing kilometres of ice to rush though and out to sea, blocking Ilulissat harbour for several days.

That made the conditions harsher, with colder water and air, and forcing Mr Pugh to deal with the sharp edges of brash ice as he swam.

But the polar regions are experiencing faster changes due to the climate crisis than anywhere else on Earth, which Mr Pugh said meant it was the best place to raise awareness.

“The reason why I did this swim is clear: we rely on ice for our survival. Ice keeps our planet cool enough for us to live. But we are losing it fast. No ice, no life.

“We have seen so many natural disasters this year – from wildfires in Greece, to floods in Germany, extreme snowstorms in Texas, but I want also everyone to be aware of what is happening here in the Arctic.”

He said he was “deeply alarmed” by what he had seen in the Arctic.

“Last month was the first time in recorded history that it rained at the highest point on the Greenland ice sheet. The melt is accelerating.

“I watched water gushing off the ice sheet at a location that, only a few years ago, was covered in hundreds of metres of ice. I also witnessed shocking quantities of ice being pushed through my swim route and far out to sea.”

Mr Pugh will take his call for action to the UN Cop26 climate conference in Glasgow in November, highlighting the role healthy oceans play in tackling climate change and calling on world leaders to protect 30% of seas by 2030.

He warned: “Unless we take urgent action to decrease global temperatures by seriously lowering our global carbon dioxide emissions, low-lying islands and coastal cities will, quite literally, drown.”