CNN  — 

Greta Thunberg’s father says he initially did not support his daughter’s climate activism, calling it a “bad idea,” but his view changed when he saw how happy it made her.

In an interview on BBC Radio 4’s Today program Monday, Svante Thunberg revealed that by skipping school and staging Friday sit-ins outside the Swedish parliament, Greta was not only battling climate change but also the crippling depression that had plagued her for up to four years.

Greta Thunberg and her father Svante attend a press conference during the COP24 summit on climate change in Katowice, Poland on December 4, 2018.

“She stopped talking, she stopped eating, and all these things,” Svante Thunberg said of Greta’s period of illness, speaking on a program guest-edited by the 16-year-old activist.

“She stopped going to school. She was basically home for a year, she didn’t eat for three months,” the 50-year-old said of what he described as “the ultimate nightmare as a parent.”

Thunberg and his wife, opera singer Malena Ernman, stopped work to look after Greta – who at that point was only speaking to them, her sister and one of her teachers at school.

So when she expressed a desire to become an activist, both parents said “quite clearly that we would not support it,” worried that she was “putting herself out there on the frontline with such a huge question like climate change.”

Change in outlook

But not only did Greta’s strikes create a powerful global movement, they helped change her outlook.

During her first sit-in outside the Swedish parliament, she began answering journalists’ questions as when they approached her. On the third day, she ate a vegan pad thai dish someone had handed to her.

“I cannot explain what a change that meant to her and to us,” Thunberg said. “And she could do things she could not have done before.”

“I can see Greta is very happy from doing this,” he added.

During the wide-ranging interview with the BBC’s Mishal Husain, Thunberg dismissed criticism that he and wife pushed Greta into becoming an activist.

“We are not climate activists, we never were,” he said, saying Greta used to call them “hypocrites” for not taking the climate issue seriously.

“We obviously did not have a clue (about) the climate crisis and she basically thought we were huge hypocrites,” he said, adding that he and his wife were longtime refugee and human rights advocates instead.

“So Greta was like ‘Whose human rights are you standing up for?” he said.

Thunberg said he “ran out of arguments” against climate activism and started to support Greta’s initiatives. His wife decided to stop flying to opera engagements and he became vegan – but it was not because of the climate crisis, he added.

“I didn’t do it to save the climate, I did it to save my child,” he said.