The days of exploration of Shackleton and Scott are long gone. Everything has been climbed, crossed, done. Now what we're exploring are the full boundaries of human endeavour. It's not physical - it's all in the head.

Going against the tide has never been difficult for me. It wasn't even a conscious decision but the natural consequence of following my own instinct.

If we pass on an unsustainable environment to our children we have failed them.

When I'm preparing for a swim, I imagine absolutely everything about it: the color of the water, how cold it is, the taste of salt in my mouth. I visualize each and every stroke.

Climate change is the Everest of all problems, the thorniest challenge facing humankind.

Of all the creatures in the world that really frighten me - the hyena in Africa, the great white shark - leopard seals are near the top of the list. They're killers. If my team spots one, they'll pull me out of the water.

Ultimately I wanted to be a pioneer swimmer, a distant descendant of Scott, Amundsen and Hillary, except that I would be an explorer of the water.