When I was born, the world's population was 3.5 billion. There are now 6.8 billion people on the planet. By 2050, that's expected to rise to 9.4 billion. What's more, the Earth's resources aren't growing; they're decreasing - and rapidly.
In the cold, all the blood rushes to your core to protect your heart, lungs, kidneys, liver, and brain. When you leave the water, the blood rushes back to your arms and legs, absorbs that freezing cold, and brings it back to the heart.
I think that I was slightly naive. I thought that if I showed people the beauty of the Arctic and the beauty of the polar bears that they would care so much that they would stand up and try to make a change.
On my second swim at Deception Island, the water was very clear and I was looking at hundreds of whale bones beneath me. It was a graveyard from the whaling some time in the 1920s-30s.
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.
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.
I've been on swims where people have freaked out about sharks. You have to think about something else, otherwise it will absolutely paralyze you. I do math problems, anything.
I just never, ever want to give up. Most battles are won in the 11th hour, and most people give up. If you give up once, it's quite hard. If you give up a second time, it's a little bit easier. Give up a third time, it's starting to become a habit.
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.
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.
