'I can see Greta is very happy from doing this', says father Svante Thunberg

Svante Thunberg, father of Swedish climate change activist Greta Thunberg said on Monday that his teenage daughter was hardly speaking to people besides her family members and went without eating for months before launching school strikes on climate change.

"First, she made a leaflet of, like, I don't know what it's like, lots and lots - 35 facts... Whenever the journalists came along, she would answer all the questions; and that was the surprising thing because she didn't speak to anyone at the time," Svante said. 

"She only spoke to me, my wife, her sister and one of her teachers," Svante added.

"Three or four years before she went on the school strike, she fell ill and stopped talking. She stopped going to school and she didn't eat for three months or two and a half months, which, of course, was the ultimate nightmare as a parent," he also said. 

"I can see Greta is very happy from doing this, " he also said.

On Monday, Greta joined forces with British naturalist and broadcaster David Attenborough to push politicians and businesses to step up action on climate change after a year in which schoolchildren took to the world's streets in protest.

Thunberg has remained at the helm of climate change advocacy and has constantly urged prominent world leaders to find viable long-term solutions.

Seen as a spokesperson for the new generation, the 16-year-old gained traction after a solo strike outside the Swedish parliament last year.

Thunberg also made headlines after her fiery speech at the United Nations climate summit where she thundered over world leaders for failing to take measure to stop global warming.

She accused them of betraying her generation by failing to tackle greenhouse gas emissions and asking "How dare you?". 

She turns 17 this week.