10/05/2013 07:29 BST | Updated 09/07/2013 06:12 BST

Amanda, Gina and Michelle Are Out of the Attic But 140Million More Girls Need Setting Free

Every two seconds, somewhere in the world, a girl becomes a child bride. Every two seconds, girls just like Amanda, Gina and Michelle are effectively being abducted, but their stories don't ever make the news.

On Monday morning came the news of three women incarcerated in an attic for ten years by a middle-aged bus driver who abducted them, one by one, when they were teenagers. A disbelieving neighbour says he used to have barbecues with the guy, never in his wildest dreams imagining that three desperate young girls - Amanda Berry, Gina DeJesus and Michelle Knight - were imprisoned in his house. I heard the story on the radio as I got ready for work and stopped in my tracks to listen, startled by its depths of depravity and abuse.

Yet on reflection, I can't help but contrast this headline news, the media frenzy, the furore around issues of child abuse and human rights, with the memories of teenage girls I've met in Africa who are, legally and openly - albeit quietly - being married off to older men; incarcerated, one might say, in a life they never wanted.

Mariama, 13, comes to mind. Mariama (pictured above) lives in a village in Niger, West Africa, and was a normal teenager, hanging out with friends, loving school, hating maths, until one morning last year when her mother informed her she was to be married to an older man she'd never met. Mariama is bewildered by the news and begs for the marriage to be stopped. But her mum Ramatou, herself married off, aged ten, to a man she says resembled her father, is determined that her daughter will meet the same fate - and Mariama drops out of school. Ramatou is worried her daughter might lose her virginity with a boy and disgrace her, she says, adding, with pragmatic candour, that she simply cannot afford for Mariama not to be married.

There's Haoua too, aged 15 and recovering in hospital after the painful birth of her first child. Haoua now suffers from incontinence and a fistula caused by the pregnancy that her body wasn't ready for. She confides her feelings that marriage isn't a happy thing and says she suffered greatly during labour. "I don't want to have children again," she adds. "I want to learn how to read."

These girls' stories, and the thousands of others from child brides around the globe, make me sad and angry in equal measure. I remember being 13, preoccupied by Michael Jackson and the latest Whitney Houston hits; best friend politics and homework. My limited knowledge of sex was gained via extensive reading of Virginia Andrews' Flowers In The Attic, a seminal text for us teenage girls at the time. Real boys were a chimera, a promising figment of the future; we knew one day we'd fall in love with a handsome boy resembling the Fonz and live happily ever after, but marriage? Marriage was something our parents did in the grown-up world we hadn't been admitted to yet. Our futures stretched before us, glinting with promise, and even if the Fonz had come along and (scream) asked us to the movies, we wouldn't have wanted to marry him.

Yet all over the developing world, young teenage girls are being married out of their childhoods, denied their right to finish school, grow up, learn, make mistakes, have their first love affair and fulfil their dreams. Instead of doing all these things, they are dropping out of school and into marriage, which severely limits the kind of future life that's available to them.

In Niger, 75% of girls are married before they reach 18; 36% before they reach 15. Nine of the 10 countries with the highest rates of child marriage are in Africa. Worldwide, more than 140 million girls will become child brides by 2020 if current rates of child marriage continue, according to the UN. All over the world, child marriage is helping drive girls into a cycle of poverty and powerlessness, affecting basic human rights and drastically affecting girls' rights to an education. Many child brides experience violence and abuse. Child brides are more likely to contract HIV, and more likely to be illiterate than their unmarried counterparts.

I work for the children's rights organisation Plan International, a charity endeavouring to end child marriage through education. Plan projects are helping ensure that girls have safe access to free schooling and are taught by qualified teachers (especially female ones), who understand girls' rights and gender equality. Getting girls into school, and keeping them there, may be one of the best ways to foster later, consensual marriage. Child marriage will no longer be the default choice for poorer parents like Ramatou, who wish to safeguard their daughters' futures. Thus, in Niger, Plan's projects include supporting education for girls, running gender training for religious leaders, NGO partners, teachers and traditional chiefs, and supporting traditional leaders to spread the message about the effects of child marriage. Around the world, Plan is working to help girls like Mariama escape child marriage, complete their secondary education and fulfil their ambitions.

Every two seconds, somewhere in the world, a girl becomes a child bride. Every two seconds, girls just like Amanda, Gina and Michelle are effectively being abducted, but their stories don't ever make the news. Let's put early and forced marriage on the global political agenda and shock the policy makers into stopping to listen. Let's urge governments to recognise child marriage as a human rights issue, and encourage them to implement integrated action plans to enable girls to avoid child marriage, stay in school and benefit from a quality education. Only by doing this can we set girls free to enjoy their futures.