The brothers on a four-month voyage through the Arctic Circle

“There is no room for error,” says Isak Rockström. “Where we are now, the only help we could get would be from the few Canadian Coast Guard icebreakers that are patrolling the whole Canadian Arctic.”

For the past two months, Isak, 26, and his brother Alex, 25, have been battling the freezing elements of the Arctic Circle together.

They have sailed through the treacherous, sometimes alien landscape of the Northwest Passage between the Atlantic and Pacific Oceans, gathering fresh data about climate change in the region.

They have faced brushes with icebergs and severe gales around Iceland.

One “tricky situation”, as Isak stoically puts it, came the day before they spoke to the BBC. While navigating a fjord, they were caught by 52mph (84kph) winds coming off the nearby mountains, dragging them towards the shore.

“The wind was so strong that with the engine on, we weren’t going anywhere,” he recalls.

Off Devon Island, the largest uninhabited island in the world, they risked running aground due to the area being poorly charted.

They had to quickly turn the other sails so the wind worked in their favour, and “take some things apart and do some jerry-rigging” to get the main sail down, Alex says.

But Isak says “the most challenging ocean crossing of my life” was the long stint around Greenland through thick fog and ice up the Davis Strait.

He says it felt like they were “trudging on and on… through either gales or fog”.

“Then one day the fog slightly lightened up and there was this little tunnel through the cloud cover in the distance – and we finally actually saw Greenland. And it was just a nice confirmation that we weren’t going crazy.”