Endurance swimmer Lewis Pugh has called for a fundamental shift at the Cop26 talks to tackle the “environmental catastrophe” of the world’s melting ice.

Speaking at the summit after undertaking a multi-day 4.8-mile (7.8km) swim two months ago in the Ilulissat Icefjord, Greenland, he warned that “glaciers are now moving quicker than our political leaders”.

Ahead of an oceans event at the Glasgow talks, the UN patron of the oceans told the PA news agency there needed to be a “complete mind shift” and an understanding incremental changes were no longer enough, as he called for leaders to act quickly on the crisis.

Ice is essential for life on Earth, he said, keeping the world within liveable temperature ranges and providing a habitat for species such as polar bears and penguins.

But Mr Pugh, who has swum in the Arctic, Antarctic and up the English Channel to raise awareness of environmental damage, warned that ice is melting in the polar regions and in the world’s mountains.

He said he had witnessed the changes to the Arctic first hand while undertaking his “brutal” swim, which took him 14 sessions over 12 days in the icy water.

They included lakes appearing on top of the ice sheets, rain in Greenland and the mass carving of glaciers, with about 60 kilometres (40 miles) of ice moving rapidly out into the ocean.

Of the glacier carving, he said: “It was awesome to watch but terrifying in equal measure.”

And he said: “I’ve been swimming in the polar regions now for 18 years, but never have I seen something so big and so dramatic.

The harsh reality is the glaciers are now moving quicker than our political leaders

“We’ve all seen the fires, we’ve all seen the storms, we’ve all seen the floods this year.

“But when you see something like this upfront, you realise the scale and the speed of the crisis.

Mr Pugh said: “So you put all these things together the rain, the supraglacial lakes and the speed of the carving which is taking place there and it paints a very, very worrying picture.”

He said leaders at Cop26 were talking variously about climate change, climate emergency or climate crisis. It is all three but, he warned, it was an “environmental catastrophe”.

“I can’t describe it in any other way – the speed and the scale of this – and the harsh reality is the glaciers are now moving quicker than our political leaders.”

He warned that there needed to be a “complete mind shift, a complete understanding that we cannot keep on with these incremental changes” at Cop26, adding “something fundamental has to shift”.

He acknowledged that long-term planning and consensus were important but urged: “But singly the most important thing now is to take action today.”

He added: “The public know what’s happening, the public are calling for change, the public are calling for urgent action, and my message to world leaders this week is we’ve got to act quickly now.”