They say three is a magic number. When it comes to temperature, I know this to be true. For a cold-water swimmer, a 3°C change makes a world of difference.The same is true for our planet.

I'm about to swim where I shouldn't be able to, for the second time in my life. All because of ice – or the lack of it.

When I decided to swim the length of the English Channel, I didn't just dive in at Land’s End and hope for the best.I assembled the very best team. We drafted a training programme. We prepared exceptionally hard. I tried to eat the correct foods. And I made sure my mind-set was right.

We were far out to sea in the English Channel, 32 days into the Long Swim, with a long way to go to Dover.I was swimming past the Isle of Wight in a serious storm and the light was fading fast. Our yacht was surging away from me in the strong winds. The swells were so big that, even if I caught up with her, I didn’t know how I would get back onboard.