A World of Difference

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.

Zero degrees

Before I started on this Greenland Swim I was hoping for an average water temperature of 3°C. But when we arrived at Ilulissat the water temperature was 0°C. We had to change my swim plan.

This is different from anything I've done before. Instead of a one-kilometre sprint, it's 7.8 kilometres over multiple days. The effects of cold are cumulative, so we decided to split each day's distance into two shorter swims, rather than one longer one, to give me time to re-warm my body in between.

Pioneering preparation

Of course the swim itself is never the most time consuming thing – the preparation and recovery take longer. Both of these are now doubled each day.

I have a top team of medical professionals looking after me. Their first concern on this swim is whether my deep body temperature will start getting lower every time I enter into the water. Their second concern is how much damage each swim is doing to my muscles and nerves. Since I have to get back in the water the next day, I need to minimise damage to my body, and my mindset. It's a delicate balance.

How do I train for a swim like this? It's a question I get asked more than any other. So here are some of the ways my team has prepared me to meet the challenges of cold water to the very best of my mental and physical abilities.

Number crunching

Let's start with defining cold. Anything below 15°C is officially classified as cold water – that's cold enough to bring on a shock response. If you've ever gone for a swim in the sea at 18°C, you would have started to feel cold after about 20 minutes. After 45 minutes the shivering comes on: that's your body's natural response to get the muscles moving and warm you up. It shouldn't take long for you to rewarm, as long as your body temperature hasn't dropped too much.

With ice swimming – technically anything less than 5°C – your body temperature is going to cool a lot quicker. Spending 20 minutes in water this cold becomes dangerous, because of the risk of hypothermia.

Hypothermia

Normal human body temperature is around 37°C; hypothermia officially begins when your core body temperature drops to 35°C. Mild hypothermia is classified as between 35° to 32°C body temperature, moderate hypothermia is between 32°C and 28°C, and severe is anything less than 28°C. My team aims to keep me above 35°C.

After years of doing this my body temperature increases before I get into the water. Starting off with a higher body temperature allows me to be in the water a little bit longer.

But here's where it gets tricky: the danger zone isn't while I'm actually in the water, it's after I get out.

The after-drop

My core body temperature doesn't fall that much while I'm actually swimming. But once I get out of the water, the relatively warm blood from my core rushes out to my extremities, and vice versa. When the colder blood hits, my core temperature plummets to potentially dangerous levels. We call this the 'after-drop'.

The antidote? Serious shivering.

Shivering can increase your metabolism by four to five times. Obviously, it's uncomfortable. Severe shivering can cause muscle damage. After my last Arctic swim, my body felt bruised all over. I wasn't just sore for four or five days – it took me months to recover. On this swim, I can't afford to be injured or damaged because I have to get back into the water twice a day.

How does my team know just how cold I am? That's where the pill comes in.

Daily capsule

I love science. Ninety minutes before every swim, I swallow a pill. Once it reaches my stomach, this little thermometer capsule measures my core temperature and sends the information to a monitor where Dr Charlotte Haldane can observe it in real time. After each swim we get a beautiful graph that tells us exactly what's been going on deep inside me. This is especially important in that critical zone after the swim. Once we're done, the pill gets deactivated and my body eliminates it within 24 to 48 hours. And no, it's not reusable – for every swim, I swallow a new pill.

Shower ban

Recovery is critical. On previous swims, the goal has been to rewarm me as quickly as possible – preferably by jumping straight into a hot shower. Such luxury! Now, though I still need to rewarm, I also need to preserve my muscles for the next day – which means no more showers.

Instead, I put on as many dry insulating layers as I can, and shiver. The rationale is that getting into a hot shower will increase the risk of nerve damage – particularly in my fingers and toes. It can also bring on a sudden drop in blood pressure, and the risk of cardiovascular collapse.

I need to wait until I've reached my lowest deep-body temperature, usually about 30 to 45 minutes after I get out of the water, before I can have a warm shower or bath.

Nutrition

Nutrition plays a major role in both my preparation and recovery. Because this is an endurance event, I need to refuel as much as possible, from sources that my body can absorb quickly. Before I swim I eat carbohydrates that release sugars into my bloodstream. When I get out of the water, the focus is on protein to replenish the muscles, and sugar to help with the shivering. Later, I'll need more carbohydrate to replenish the glycogen that's been depleted from both the shivering and the swimming.

I always crave a warm drink after a swim, but it's the sugar, not the temperature, that's really important. Luckily hot chocolate ticks all the boxes!

Preparing my body

No matter how much cold-water adaptation you do, you will still get very cold. So the goal is to cover the swim distance as quickly as possible.

I trained for six months in cold water off Cape Town before my 10 days of very cold-water preparation in Iceland. I trained in the open ocean, but also in the pool to improve my swimming efficiency and cardiovascular fitness. The better my technique, the quicker and more efficient I am in the water.

Muscles don't work as effectively in cold water, so I needed to build extra strength. But since blood flows to muscles to get them moving, the more muscle you have, the quicker you lose heat in cold water.

I needed to be more like a seal.

Ideal insulation

It's all about insulation. Fat is what's really important when it comes to keeping warm.

The science is fascinating: each millimetre of subcutaneous fat is equivalent to raising the temperature of the water you're swimming in by one-and-a-half degrees Celsius. A layer of fat over the muscle helps keep the heat inside. My training focused on getting as strong, fit and efficient in the water as possible – and adding a bit of strategic padding.

Gentle immersion

Faced with a kilometre of icy water, my tendency is to dive in and go. But our strategy has shifted towards what my team calls a 'gentle immersion'. They've asked me to wait in the water for 30 seconds before I actually start swimming. It's excruciating, but there's solid science behind it: if I get my breathing under control before I start, I'll be that much more efficient once I begin swimming. Now I spend that time adjusting my cap and goggles.

Even when breathing well, a 0.5 to two degree drop in core body temperature can decrease your maximum oxygen consumption – or VO2 max – by up to 30%. Not only does less oxygen affect performance, but your body switches into anaerobic metabolism, producing more lactate, which creates fatigue.

Dodging ice traffic

All of these preparations involve things we can control. But Mother Nature makes her own plans. Each day in Ilulissat has brought new challenges. A strong mind is as important as peak physical condition, but it can't be so strong as to override your survival instinct – the pain is telling you that you're in danger. It's a fine line.

As we have crossed halfway, I'm certainly feeling the effects of the cold. My body is sore. And at night I keep asking myself how much longer I can keep this up. But somehow I'll keep going; I've got a very good reason to.

Planet emergency

When it comes to our heating planet, we don't have a three-degree margin. Scientists tell us that a 2°C increase above pre-industrial temperatures will push us past a point of no return. The latest IPCC report suggests that we have already exceeded 1.5°C.

Our Earth evolved as a complex living system in delicate balance. In the same way that I need to make adjustments to my body to deal with the extreme cold, we need to make serious changes to stop our planet from heating up any further.

I'm freezing here, to remind world leaders that if we push our planet too far, all our lives are at risk.

There is a world of difference in just 2°C. Let's not put this number to the ultimate test.

Lewis Pugh is an endurance swimmer and the UN Patron of the Oceans.
He was the first person to swim the 528km length of the English Channel.