Last year when I was here, I was speaking to you about a swim which I did across the North Pole. And while that swim took place three years ago, I can remember it as if it was yesterday. I remember standing on the edge of the ice, about to dive into the water, and thinking to myself, I have never ever seen any place on this earth which is just so frightening. The water is completely black. The water is minus 1.7 degrees centigrade, or 29 degrees Fahrenheit. It's flipping freezing in that water. And then a thought came across my mind: if things go pear-shaped on this swim, how long will it take for my frozen body to sink the four and a half kilometers to the bottom of the ocean? And then I said to myself, I've just got to get this thought out of my mind as quickly as possible. And the only way I can dive into that freezing cold water and swim a kilometer is by listening to my iPod and really revving myself up, listening to everything from beautiful opera all the way across to Puff Daddy, and then committing myself a hundred percent -- there is nothing more powerful than the made-up mind -- and then walking up to the edge of the ice and just diving into the water. And that swim took me 18 minutes and 50 seconds, and it felt like 18 days. And I remember getting out of the water and my hands feeling so painful and looking down at my fingers, and my fingers were literally the size of sausages because -- you know, we're made partially of water -- when water freezes it expands, and so the cells in my fingers had frozen and expanded and burst. And the most immediate thought when I came out of that water was the following: I'm never, ever going to do another cold water swim in my life again. Anyway, last year, I heard about the Himalayas and the melting of the -- (Laughter) and the melting of the glaciers because of climate change. I heard about this lake, Lake Imja. This lake has been formed in the last couple of years because of the melting of the glacier. The glacier's gone all the way up the mountain and left in its place this big lake. And I firmly believe that what we're seeing in the Himalayas is the next great, big battleground on this earth. Nearly two billion people -- so one in three people on this earth -- rely on the water from the Himalayas. And with a population increasing as quickly as it is, and with the water supply from these glaciers -- because of climate change -- decreasing so much, I think we have a real risk of instability. North, you've got China; south, you've India, Pakistan, Bangladesh, all these countries. And so I decided to walk up to Mt. Everest, the highest mountain on this earth, and go and do a symbolic swim underneath the summit of Mt. Everest. Now, I don't know if any of you have had the opportunity to go to Mt. Everest, but it's quite an ordeal getting up there. 28 great, big, powerful yaks carrying all the equipment up onto this mountain -- I don't just have my Speedo, but there's a big film crew who then send all the images around the world. The other thing which was so challenging about this swim is not just the altitude. I wanted to do the swim at 5,300 meters above sea level. So it's right up in the heavens. It's very, very difficult to breath. You get altitude sickness. I feels like you've got a man standing behind you with a hammer just hitting your head all the time. That's not the worst part of it. The worst part was this year was the year where they decided to do a big cleanup operation on Mt. Everest. Many, many people have died on Mt. Everest, and this was the year they decided to go and recover all the bodies of the mountaineers and then bring them down the mountain. And when you're walking up the mountain to attempt to do something which no human has ever done before, and, in fact, no fish -- there are no fish up there swimming at 5,300 meters -- When you're trying to do that, and then the bodies are coming past you, it humbles you, and you also realize very, very clearly that nature is so much more powerful than we are. And we walked up this pathway, all the way up. And to the right hand side of us was this great Khumbu Glacier. And all the way along the glacier we saw these big pools of melting ice. And then we got up to this small lake underneath the summit of Mt. Everest, and I prepared myself the same way as I've always prepared myself, for this swim which was going to be so very difficult. I put on my iPod, I listened to some music, I got myself as aggressive as possible -- but controlled aggression -- and then I hurled myself into that water. I swam as quickly as I could for the first hundred meters, and then I realized very, very quickly, I had a huge problem on my hands. I could barely breathe. I was gasping for air. I then began to choke, and then it quickly led to me vomiting in the water. And it all happened so quickly: I then -- I don't know how it happened -- but I went underwater. And luckily, the water was quite shallow, and I was able to push myself off the bottom of the lake and get up and then take another gasp of air. And then I said, carry on. Carry on. Carry on. I carried on for another five or six strokes, and then I had nothing in my body, and I went down to the bottom of the lake. And I don't where I got it from, but I was able to somehow pull myself up and as quickly as possible get to the side of the lake. I've heard it said that drowning is the most peaceful death that you can have. I have never, ever heard such utter bollocks. (Laughter) It is the most frightening and panicky feeling that you can have. I got myself to the side of the lake. My crew grabbed me, and then we walked as quickly as we could down -- over the rubble -- down to our camp. And there, we sat down, and we did a debrief about what had gone wrong there on Mt. Everest. And my team just gave it to me straight. They said, Lewis, you need to have a radical tactical shift if you want to do this swim. Every single thing which you have learned in the past 23 years of swimming, you must forget. Every single thing which you learned when you were serving in the British army, about speed and aggression, you put that to one side. We want you to walk up the hill in another two days' time. Take some time to rest and think about things. We want you to walk up the mountain in two days' time, and instead of swimming fast, swim as slowly as possible. Instead of swimming crawl, swim breaststroke. And remember, never ever swim with aggression. This is the time to swim with real humility. And so we walked back up to the mountain two days later. And I stood there on the edge of the lake, and I looked up at Mt. Everest -- and she is one of the most beautiful mountains on the earth -- and I said to myself, just do this slowly. And I swam across the lake. And I can't begin to tell you how good I felt when I came to the other side. But I learned two very, very important lessons there on Mt. Everest, and I thank my team of Sherpas who taught me this. The first one is that just because something has worked in the past so well, doesn't mean it's going to work in the future. And similarly, now, before I do anything, I ask myself what type of mindset do I require to successfully complete a task. And taking that into the world of climate change -- which is, frankly, the Mt. Everest of all problems -- just because we've lived the way we have lived for so long, just because we have consumed the way we have for so long and populated the earth the way we have for so long, doesn't mean that we can carry on the way we are carrying on. The warning signs are all there. When I was born, the world's population was 3.5 billion people. We're now 6.8 billion people, and we're expected to be 9 billion people by 2050. And then the second lesson, the radical, tactical shift. And I've come here to ask you today: what radical tactical shift can you take in your relationship to the environment, which will ensure that our children and our grandchildren live in a safe world and a secure world, and most importantly, in a sustainable world? And I ask you, please, to go away from here and think about that one radical tactical shift which you could make, which will make that big difference, and then commit a hundred percent to doing it. Blog about it, tweet about it, talk about it, and commit a hundred percent, because very, very few things are impossible to achieve if we really put our whole minds to it. So thank you very, very much. (Applause)