If you want to swim across the English Channel from England to France - you have to leave your doubt on the beach in England.

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.

The blues is also existential and offers a sense of mature reflection that enabled it to be the leitmotif of modern life.

I learned two basic lessons on Everest. First, just because something has worked in the past does not mean it will work today. Second, different challenges require different mindsets.

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.

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

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