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Do you feel an emotional connection to sea ice?

Yes, there is a mysterious attraction. You are at sea and you know there are thousands of metres of water underneath you, but the ice is like a landscape. It鈥檚 beautiful. Besides, there鈥檚 the wildlife 鈥� polar bears, seals and whales. There is nothing there except nature and that is very, very attractive.

You first traversed the North-West Passage in 1970. How does today鈥檚 ice compare with what you experienced back then?

I was on a Canadian oceanographic ship, the . Our ship was ice-strengthened but still got stuck. We had to be rescued by a proper icebreaker.

I really got a good feel for the thickness of the ice in 1972 when I started working with Royal Navy submarines in the Arctic. We sailed underneath the ice for the first big surveys of its thickness. In those days, nearly all of it was multi-year ice, which can grow to 3 to 4 metres thick. You also got ridges up to 50 metres thick, where the ice piled up because of the wind. It鈥檚 a very, very rugged surface, and it seemed that was how it would be forever.

Now that multi-year ice is nearly all gone. Most of the ice that forms in the winter melts again in the summer, so it is mostly only 1 to 1.5 metres thick, and it has lots of openings. A completely different landscape.

What was it like under thick ice in a submarine?

The very first submarine I went was on was diesel. It had to surface every day to charge batteries, so it was quite daring to go under the ice. My subsequent voyages were on nuclear submarines. Working under the ice was really exciting at first. But as I got older, I got claustrophobic 鈥� there isn鈥檛 very much space in a submarine. We never had anything go wrong except for the last voyage in 2007, where we had a very serious accident.

What happened?

There was an explosion and fire in the submarine while we were underneath the ice. An air purification system blew up. Two sailors were killed, and the entire submarine was very nearly lost. We had to spend about 3 hours wearing breathing masks, because there was smoke throughout the submarine. The captain finally got us up through the ice. Fortunately for us, we were very close to an American camp.

Were you scared?

When the explosion happened I was pretty sure I was going to die in the next few seconds 鈥� if you are in a submarine underwater and an explosion happens, generally speaking, that鈥檚 it. Amazingly, I didn鈥檛 feel frightened at all.

When we talk of an ice-free Arctic, it鈥檚 not as if the entire Arctic will be devoid of ice, is it?

Ice-free means that there will be less than a million square kilometres of sea ice remaining in September, which is the month of least ice cover. You鈥檇 expect the ice to withdraw from the centre of the Arctic, towards the coastlines of Ellesmere Island and Greenland. The North Pole will likely be without ice.

What is the expectation for this year?

Looks like it鈥檚 , but there will be enough ice left that you can鈥檛 really say it鈥檚 ice-free. But the trend is so strongly downwards that in one, two or three more years, I expect an ice-free September.

A few years ago oceanographer Wies艂aw Mas艂owski predicted we鈥檇 be ice-free by now and you agreed with him. Do you worry about crying wolf?

I鈥檝e been accused of that, but I鈥檇 refute it very strongly. If you look at the trend of ice volume in September it points to us being ice-free around this year, but annual wiggles and random variability will always occur. It鈥檚 only that random variability that is keeping some ice at the moment.

What happens once the Arctic is ice-free?

It could lead to what Mark Serreze at the University of Colorado in Boulder called the Arctic death spiral. The retreat of sea ice drives feedback warming effects which are actually more serious than the retreat itself. Besides the decreasing extent of sea ice, the snow line on land is also retreating. The snow cover in the northern hemisphere has gone down by about 6 million square kilometres in the last few years, which is comparable to the loss of sea-ice cover. All this is replacing a white surface with a dark surface, which absorbs more sunlight instead of reflecting it. This means we are on the way towards runaway global warming 鈥� the feedback will result in greater warming than is caused directly by greenhouse gases. That鈥檚 really worrying.

Another serious impact that鈥檚 not being considered properly is the possibility of offshore methane bursts from the continental shelves. Methane is a very powerful greenhouse gas.

How might a methane release happen?

In the last 10 years, the sea ice has retreated from the shallow Arctic shelves. That means the sun heats this coastal water for three or four months. Because the water is shallow, that heat gets down to the seabed. There has been permafrost there since the last ice age, but now it鈥檚 thawing. And underneath the permafrost, in the sediments, are huge amounts of methane in the form of methane hydrates. As that protective cap of permafrost thaws, they turn into methane, bubble up to the surface and are emitted into the atmosphere.

鈥淭he disappearance of sea ice is like people blowing up statues of the Buddha鈥�

The amount of methane stored in Arctic permafrost is hotly contested. How can we get at the truth?

I鈥檓 hoping to go out myself next year. The Scripps Institution of Oceanography in California has an electromagnetic instrument that is towed behind a ship to detect methane hydrates in sediments and estimate the quantity. So, we will directly measure how much methane hydrate there is and that will help to resolve this question.

In your book, you wrote that losing the Arctic ice is akin to a 鈥渟piritual impoverishment of Earth鈥�. What did you mean?

The disappearance of Arctic sea ice is the disappearance of something very beautiful. It鈥檚 like people blowing up statues of the Buddha. We have already lost the kind of magnificent landscapes of sea ice that existed when I was young. When it goes completely, the world will be a sadder place.

And it will affect people鈥檚 mentality. So long as sea ice existed in the Arctic, it connected all the inhabited parts of the northern hemisphere. But when it goes, there will be an ocean between Siberia and North America and Greenland. It will take away a source of unity.

This article appeared in print under the headline 鈥淥n the top of the world, looking down on disaster鈥�