Lea is the second-youngest Unicef ambassador of all time and the first climate activist to be chosen as an ambassador, the NGO writes on its website.
The teenager has been engaged in climate issues since she was eight years old and was elected to the board of Eco-Agents, an environmental organization for children, at the age of 11, according to the Unicef Norway website.
She has been particularly prominent in climate protests in Norway over the last six months, during which time she has appeared on a series of stages across the country to give speeches during demonstrations.
Her activism also includes heading the Norwegian Children’s Climate Panel (Barnas Klimapanel) and taking part in an appeal during the UN climate talks in Bonn.
“It feels very meaningful to work with Unicef, which works for children’s rights,” the 15-year-old told NRK.
“Climate changes impact very unequally, (but) particularly on children. So it’s important for us to stand together. I will fight to give myself, my friends, people and the next generation the chance to live,” she added.
Unicef Norway general secretary Camilla Viken praised Lea's talent and ambition and said she looked forward to working with her.
“We want to work with Penelope because she has been a clear and strong voice on an area of great importance for her and many children: climate,” Viken told NRK.
“Furthermore, she has campaigned for children to be given the opportunity to put across their views and be heard,” Viken added.
Unicef Norway last appointed an ambassador, former alpine ski racer Kjetil André Aamodt, 12 years ago. The NGO’s other national ambassadors are former footballer and current Manchester United manager Ole Gunnar Solskjær and soprano singer Sissel Kyrkjebø, while actress and director Liv Ullmann is an international ambassador for the Norwegian charity.