Before Greta Thunberg became the face of the global climate movement, before she was Time magazine’s Person of the Year and a nominee for the Nobel Peace Prize, she was an 11-year-old child who suddenly stopped eating.

The world knows her best for what came after: She is the teenage prophet who travels the world by sailboat to spread her message, the unflinching activist who protests leaders at the World Economic Forum in Davos, the impassioned speaker who sat before leaders of the United Nations and famously demanded of them, “How dare you?”

But in “Our House Is On Fire: Scenes of a Family and a Planet in Crisis,” a memoir by Thunberg’s family to be published Tuesday, a more vulnerable and intimate portrait emerges in the telling of Thunberg’s origin story - an account rooted in what it felt like to be the terrified parents of a child facing a devastating crisis of her own. (Thunberg’s parents, Malena Ernman and Svante Thunberg, are listed as authors alongside Greta Thunberg and her sister, Beata Ernman, but the book is narrated by Thunberg’s mother.)

“She cried at night when she should have been sleeping. She cried on her way to school. She cried in her classes and during her breaks, and the teachers called home almost every day,” Ernman writes, recalling her fifth-grader’s sudden spiral in 2014. “She had disappeared into some kind of darkness and appeared to stop functioning.”

Thunberg had stopped playing piano, stopped laughing, stopped talking. She would eat only minuscule bites of certain foods prepared in a certain way by her agonized parents, who watched as it took their daughter hours to finish a plate of three or four gnocchi. Within months, Thunberg had lost 20 pounds, and her pulse and blood pressure showed signs of starvation.

Thunberg’s parents have referred to this bleak period before, but their memoir offers searing details of what it felt like to watch her harrowing descent. The catalyst, Ernman writes, was a video about climate change that Thunberg viewed at school, footage of a massive island of plastic adrift in the South Pacific. Thunberg wept as she watched.

Other students seemed able to easily compartmentalize the reality of what they’d seen, but Thunberg could not stop thinking about it, Ernman writes, to the point that she could no longer function in daily life.

Thunberg, who was eventually diagnosed with Asperger’s syndrome and obsessive-compulsive disorder, has often spoken of the way her autism has shaped how she perceives the world and the threats against it - how it helps her see the climate crisis in “black and white.” In the family’s book, her mother describes this perspective as a clarifying gift.

“Greta has a diagnosis,” Ernman writes, “but it doesn’t rule out the fact that she’s right and the rest of us have got it all wrong.”

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Greta Thunberg’s ascent has been plagued by debunked conspiracy theories, hoaxes and seething accusations aimed at her parents, alleging that the teenager is merely a puppet used to further their agenda - that she is indoctrinated, manipulated, brainwashed.

“Our House Is On Fire” is a resounding rejection of those false claims. Ernman depicts how Thunberg’s recovery from her mental health crisis was bolstered by her activism, and specifically her choice to skip school in August 2018, when she sat outside the Swedish Parliament clutching a sign that read “Skolstrejk för klimatet”: “School strike for climate.”

Her parents had no idea this simple action would launch a global movement. They were not enthusiastic about her plan, Ernman says; they were concerned about the attention they knew it would draw to their child, who had only just begun to reclaim some semblance of normalcy in her life. But as they watched their daughter prepare for the strike, they saw that she felt good, Ernman writes, better than she had felt “in many years.”

Even then, Svante Thunberg worried that people would not believe his daughter had come up with this idea herself - that a teenager could be so passionate, driven and informed about the climate crisis. That she was the one who had persuaded her parents of the urgent need to act, and not vice versa.

“ ‘Did your parents put you up to this?’ You’re going to get that question all the time,” her father warned her, as Ernman recounts. Thunberg responded: “Then I’ll tell it like it is. I’m the one who influenced you and not the other way around.”

The speed and scope of the exposure that followed Thunberg’s strike was stunning. Amid the whirlwind, small but vivid moments stand out in Ernman’s recollection: Their daughter spoke to curious passersby and answered questions from journalists who stopped to interview her. She ate an entire container of vegan noodles delivered to her by a friend on the third day of her strike. No one but her parents could appreciate why this was remarkable.

“I promise that any parent whose child hasn’t talked to people for several years and who could eat only a few things in a few predetermined places will be extremely happy to see those complications vanish,” Ernman writes. “Almost like a fairy tale.”

As Thunberg’s profile grew, so did the hatred directed at her; she soon began receiving death threats. The family was sent excrement in the mail, and her parents were the subject of complaints logged with local social service agencies.

“Somehow I am starting to realize that they are going to take my child from me,” Ernman writes. “She might not be able to keep on living here. The price of being heard is hate. The price of being seen is hate.”

The book does not follow the family fully into the stratosphere of Thunberg’s stardom; it ends before Ernman can explain what it was like to watch her child rise to a global stage and become the target of vitriol lobbed by her most powerful and prominent critics (President Donald Trump has repeatedly mocked the young activist on Twitter; most recently, Thunberg was the subject of a vulgar sticker distributed by a Canadian oil company that depicted her as the victim of a sexual assault).

But the family’s account conveys the sense that, despite the risk and cost of Thunberg’s prominent place in the climate movement, for her parents - who once wondered whether she would speak again and carefully chronicled every tiny meal she consumed over the course of hours - there is, above all, a profound sense of relief.

In one of the book’s final chapters, Ernman describes the first time her daughter spoke before a large crowd, at the People’s Climate March in Stockholm. Thunberg had never addressed more than a classroom-sized gathering of people, and even that had made her uncomfortable. But on the day of the march, she calmly approached the microphone and began speaking with clarity and confidence. Her astonished father watched from the crowd.

“You must be very proud,” a woman told him.

At that moment, Thunberg hovered on the cusp of all she would soon become: famous, beloved, reviled, respected, feared, celebrated. But what her father saw was that his child finally seemed like she was going to be OK.

“Proud?” he said, shouting to be heard over the crowd’s ovation for his daughter. “No, I’m not proud. I’m just so endlessly happy because I can see that she’s feeling good.”