Here are some things to know about Thunberg:
Thunberg is the eldest of two girls and is the daughter of actor Svante Thunberg and opera singer Malena Ernman. She was born Jan. 3, 2003, in Stockholm, Sweden.
She is distantly related to Svante August Arrhenius, the first scientist to predict that carbon emissions would lead to global warming. He received the Nobel Prize for chemistry in 1903, becoming the first Nobel laureate from Sweden.
Thunberg arrived in the United States in late August after traveling across the Atlantic Ocean by sailboat, NBC News reported. The trip took weeks and was emission-free, the network reported. She refuses to fly.
In November 2018, Thunberg stood outside the Swedish parliament and held a placard that read, "School strike for the climate." She skipped school every Friday for the last year and is taking the 2019-2020 school year off, according to The Federalist.
Thunberg was featured on the cover of Time magazine on May 27, 2019. This month, she also made the magazine's list of Women Who Will Change the World.
She and her sister, Beata, have been diagnosed with a form of autism, ADHD and other conditions. Thunberg calls her condition her "superpower," which she says allows her to speak more directly about climate change, The Atlantic reported.
"I see the world a bit different, from another perspective," she told the New Yorker. "It's very common that people on the autism spectrum have a special interest. … I can do the same thing for hours."
In March, Norwegian lawmaker Freddy André Øvstegård told news outlets he had nominated Thunberg for the Nobel Peace Prize, Huffington Post reported.
The winner of this year's Nobel Peace Prize will be announced Oct. 11, according to the organization.
Some of Thunberg's critics believe she has been manipulated by left-wing extremists.
“This child -- and she is a child -- has been scared and her parents are letting her be controlled by that fear,” columnist Erick Erickson wrote. Erickson blames Thunberg's parents for "depriving her of a sound education so she can lecture grownups.”
Jonathan Tobin, at The Federalist, worries that the shoe is on the other foot: Thunberg has "forced her parents to adopt a vegan diet" and "bullied her mother to give up her career because it involved air travel."