FIRST contact can be scary, even for someone like Caroline Ciavaldini. Sometimes, before it all starts, the 32-year-old climber will stand at the bottom of a rockface, look up and think: can I do this? But then she puts her hand on the stone and it starts to happen all over again. Something extraordinary takes over when she's on a climb, she says; once she's up there, she is a new combination of muscle and mind. It's like she changes – mentally and physically.

Or to put it another way: it's like she disappears. Climbing, says Ciavaldini, is not like other sports. If you're a runner, you have free space in your head to think, but climbing is different. There's no time to fret about your worries. "You have to focus on so many things at the same time and the intensity of the focus you need is unique," she says. "I think that's why people like climbing, ideally outdoors, but indoors it's the same: you disappear."

This effect, says Ciavaldini – this disappearing act – makes climbing a sort of therapy for those who do it, but for Ciavaldini it's also something that has always been there. She first took up climbing when she was a child growing up on the small island of Reunion in the Indian Ocean and she is now one of the world's leading professional climbers. The rockface is where she goes to work.

However, she also wants to spread the word about what she does, and convert others to the lifestyle if she can. When I call her, she tries to convince me to take up climbing and in some ways I can see what she's on about. Ciavaldini, who's French, has just written a book with her British husband and fellow climber James Pearson and it's full of pictures that show what humans are capable of. There are shots of Ciavaldini hanging from her fingers above a 400m drop, or scaling what looks like a sheer smooth rock; this is a woman who thinks nothing of camping out on a tiny ledge, held to the side of a cliff with wires. It is flesh and stone in a seemingly impossible relationship.

But there are questions. Obvious questions, about danger and the risk of death, and Ciavaldini is prepared to answer all of them honestly. Everyone is afraid of heights, she says, including her, but climbing is about the art of controlling the fear. She is also not afraid of death, she says, and if she and her husband were to die, then she hopes their friends and family wouldn't feel sad because she and Pearson have had an amazing life. "In an ideal world," she says. "if we die, we die together."

When we talk via Skype, Ciavaldini is at her home in France and, as well as discussing the risks of what she does, she talks me through some of her most extraordinary experiences, such as camping overnight on small ledges no bigger than single beds that are pegged to sheer cliff-faces. The pictures of climbers pitching their camps in this way are among the most astonishing in Ciavaldini's book, but she is matter-of-fact when she describes how it works.

"You climb until it's dark and then you have to stop," she says. "You have a little dinner – dehydrated food, and it takes time, because you are attached all the time. It's cold as well, so you melt the snow for water. And by the time you have dinner, all you want to do is chill. You don't sleep. The last time, I was cold, I didn't really sleep but my body still rests. You are still resting." Resting on a ledge in the air.

Ciavaldini has camped in this way several times, but it's just another of the challenges she has taken on. When she's thinking about what climb to do next, as she is doing now, the level of difficulty is one of the factors that comes into play, as well as the history of the route, who has done it and how they did it.

"There is a lot about the history and who has opened the line," she says. "In the UK, this is very relevant – there is a huge history of climbing and there are big names associated with routes. You think I want to do that because you have a lot of respect for that person." But sometimes, she says, it's just a picture of a rock or a mountain that sparks the idea of a climb – it's beautiful and you think, I need to do it.

The planning beforehand is long and meticulous, but arriving at base camp can still be intimidating. "You need to be ready to be patient but in general first contact is quite scary," she says. "You are at the foot of a 400m rock and you're like, 'Oh my god'. It looks like a big sum of things to manage. I'm not worried about height because I've done it so much. It's more like I'm scared: can I manage that? It looks scary because sometimes the rock seems loose, sometimes it's overhanging." She says that, despite all her experience, she can still be over-awed.

The technique she applies to a climb is one she developed in the 10 years that she was a competitive climber. She figured out that the one way not to be stressed was to focus on one thing at a time. "I remember my little routine when I was doing competition; my little trick was to just focus on the first four or five movements and try to focus on the happiness; the fact that the movements were really interesting and I was looking forward to trying them."

So does climbing make her happy then? "I don't know if it makes me happy in the moment because I disappear but the anticipation is happiness. I've got some memories of me being happy while climbing but this is usually once I have finished a hard section. I can be just enjoying the quality of the rock but I know I am not going to fall and I can just take a step back from myself and look at myself in my environment." Sometimes, she says, when she looks at pictures of herself, like the ones in her book, Climbing Beyond, it's like looking at pictures of someone else – she was so focused at the time that she can't remember what happened. "I am not autistic or anything, but you could always ask me what methods I had planned, but you could not ask me what methods I had actually used," she says.

I ask if there tends to be an obsessive streak in climbers. Is there a particular type of person that's attracted to climbing? Ciavaldini thinks not, but she does see a pattern. "The one single trait I can see is you create a community and you start belonging to it – you share a culture. Climbers are a nationality in the sense that even if you meet climbers who do not have the same language, you have a common point straight away and you instantly belong and become friends and share things."

This certainly applies to Ciavaldini and her husband. They met in Turkey and the connection was instant; they have now been married for seven years and are pretty much together 24/7. They get on well, she says, but they argue sometimes, and there's a competitive element to their relationship. Ciavaldini thinks the climbing community is about 60/40 men/women, but women can have the competitive advantage: they are more flexible, have smaller fingers and can be lighter. "I didn't feel like I had to fight for my own place. I've never felt like I need to. I'm quite tough – I would never let guys stand on my toes. Most of the time I can beat them."

Ciavaldini says she and her husband have talked about the dangers in what they do, because they have to, and says her own attitude to risk has evolved over time, from the relatively safe competitive sport climbing to the more dangerous form of trad climbing that she practises now. Unlike sport or indoor routes, trad routes do not have bolts on them – instead, the lead climber places protection such as nuts in cracks as they go.

"I did not start climbing for the risk," she says. "Sport climbing is a bit like driving. It's the same. You could make a mistake when you're driving and you come off the highway and you're dead so sport climbing is not any more dangerous than driving. James started as a trad climber originally so his approach was always about danger, it was always about daring and finding the balance between 'I can do it' and 'I should not do that'. The big thing about trad climbing is to learn to take the decision to commit or not commit."

The way Ciavaldini has coped with the risk is by increasing it in small steps. "Some people are really adventurous and are ready to take risks right away but that was not my approach. I need to decide where I want to stop with risk-taking because right now, I find it totally acceptable but years ago if I had looked at the person I am now, I would have said, 'oh my god, she's nuts, she's going to kill herself'. There is no black and white. There is no answer."

As for the ultimate risk – death – Ciavaldini is sanguine. "I have no problem with dying because I have an amazing life and realistically if I die, it is not the end of the world – the world will move on no problem. The greatest difficulty is for the people who stay so if James dies with me, I think maybe that's fine and we are quite relentless about speaking to our families that we are totally OK with that and we accept that risk. I am very close to my sister and she is constantly worried about me. I keep trying to explain to her that a) she shouldn't be worried and b) it's my choice and c) I have an amazing life and it doesn't matter if it stops soon."

In many ways, Ciavaldini also sees climbing as quite the opposite of death – as a life-force and healer. Sometimes, she'll be feeling sick or sore and thinking that she is in no condition to climb, and then, when she starts climbing, all the symptoms vanish. It's the disappearing act again, the magic trick that climbing performs on her, and the higher she goes, the more it works.

Climbing Beyond, by James Pearson and Caroline Ciavaldini, is published by Aurum at £25