Thunberg has said she learned about climate change at age 8, and didn't understand why adults weren't acting to mitigate its effects. By age 11, she became depressed by the seemingly impossible task of saving the planet.
In May 2018, Thunberg won a climate-change essay competition for the Swedish newspaper Svenska Dagbladet. It was the genesis of her activism career. She started the School Strike for Climate effort three months later, and launched her first protest three months after that.
Thunberg partially credits her Asperger's syndrome for her fierce activist nature. She was diagnosed four years ago.
In an interview with BBC journalist Nick Robinson, Thunberg said that "being different is a gift." If she didn't have Asperger's, Thunberg added, she wouldn't have become such a passionate climate activist.
Thunberg has also tweeted about her condition, saying that having Asperger's is a "superpower."
In December, Thunberg spoke at the 2018 United Nations climate change conference in Katowice, Poland.
"This is the biggest crisis humanity has ever faced," she told UN secretary general António Guterres before the conference started. "First we have to realize this and then as fast as possible do something to stop the emissions and try to save what we can save."
Three months later, on March 15, 2019, Thunberg led more than 1 million students around the world to walk out of their Friday classes to protest inaction on climate change.
Young people in more than 123 countries skipped school to demand more robust climate policies and the reduction of greenhouse-gas emissions.
Thunberg spoke at the Stockholm demonstration during that global event.
"We have only been born into this world, we are going to have to live with this crisis our whole lives. So will our children and grandchildren and coming generations," she said, according to Reuters. "We are not going to accept this. We are striking because we want a future and we are going to carry on."
As a commendation of her leadership, Thunberg was nominated for the Nobel Peace Prize.
She "has launched a mass movement which I see as a major contribution to peace," Norwegian Socialist MP Freddy André Øvstegård told the Guardian. "We have proposed Greta Thunberg because if we do nothing to halt climate change it will be the cause of wars, conflict, and refugees."
Thunberg's fame has continued to grow since the March strike and her Nobel Peace Prize nomination. In April, Thunberg briefly spoke with Pope Francis during the weekly general audience at the Vatican.
The Pope has made it clear that he strongly supports action to curb climate change.
"Thank you for standing up for the climate and speaking the truth. It means a lot," Thunberg told him.
"God bless you, continue to work, continue. Go along, go ahead," he responded.
A week after that, Thunberg spoke to UK parliament leaders: "Many of you appear concerned that we are wasting valuable lesson time, but I assure you we will go back to school the moment you start listening to science and give us a future. Is that really too much to ask?"
Thunberg has also met with UN leaders on numerous occasions and visited the French Parliament.
But because airplane travel has a heavy carbon footprint, Thunberg refuses to board any airplanes. In Europe, she typically travels by train. But crossing the Atlantic posed a new challenge.
A single round-trip flight between New York and California generates roughly 20% of the greenhouse gases your car emits in a year.
Thunberg enlisted the help of Boris Herrmann, who captains a schooner named Malizia II. The ship runs on solar power and underwater turbines (in addition to wind, of course), thereby generating electrical power with zero carbon emissions.
After a 13-day journey, Thunberg arrived in New York City on August 28 with her crewmates: her father Svante, professional sailors Boris Herrmann and Pierre Casiraghi, and filmmaker Nathan Grossman.
Since arriving in the US, Thunberg has been busy.
On Tuesday, Thunberg sat down with former President Barack Obama to talk about climate change in Washington, DC. The two met at the headquarters of the Obama Foundation.
"My message to young people who want to have an impact on the world is to be creative," Thunberg said in a video of the meeting shared by the Obama Foundation. "There's so incredibly much you can do and do not underestimate yourself."
"Just 16, @GretaThunberg is already one of our planet's greatest advocates," Obama tweeted after their meeting.
The same day, she attended a meeting with US lawmakers to discuss policies on climate change.
Thunberg's remarks at the hearing on Wednesday lasted less than one minute. Instead of a prepared speech, Thunberg simply submitted a 2018 United Nations report on climate change to the lawmakers.
"I don't want you to listen to me," she said. "I want you to listen to the scientists."
On Friday, Thunberg will attend a worldwide climate strike that is expected to be even larger than the one in March.
Four months after the global youth strike, adults will join the ranks of young protesters in most major cities across 156 countries. Thunberg will appear at the New York City Global Climate Strike demonstration, which will start at 12 p.m. ET in Manhattan's Foley Square.
According to the movement's website, strikes are scheduled on two different dates, September 20 and 27, to promote sustained action as opposed to a one-time protest.
It's likely to be the biggest climate-change protest in history.
Then on Saturday, Thunberg will speak at the UN Youth Climate Summit.
UN Secretary General Guterres has urged countries to put forward concrete plans to upgrade their national carbon-emissions goals by the 2020 deadline set in the Paris climate agreement. Summit organizers have also encouraged countries to set goals to reach carbon neutrality by 2050, and Guterres is calling for an end to coal use after 2020.
Following her engagements in New York, Thunberg plans to travel throughout the US, Canada, and Mexico, then attend the annual UN Climate Change Conference (COP25) in Santiago, Chile in December.
She has said that she wants to meet with people most impacted by the climate crisis, as well as other activists and influential decision-makers. Thunberg plans to travel to Chile in December via trains and buses.
"During the past year, millions of young people have raised their voice to make world leaders wake up to the climate and ecological emergency. Over the next months, the events in New York and Santiago de Chile will show if they have listened," Thunberg said in a press release.
She added: "Together with many other young people across the Americas and the world, I will be there, even if the journey will be long and challenging."
