She started a global movement at the age of 15, dominated headlines and became TIME’s youngest ever individual Person of the Year in 2019. But Greta Thunberg was understated when reflecting on her year. “I have not accomplished anything,” she told TIME in Lisbon, after a rough trans-Atlantic sailing trip brought her back from a four-month climate strike tour around North America. “I have just acted on my conscience and done what everyone should be doing.”

Acting on her conscience has spurred millions around the world to act, whether it’s eating less meat, eschewing air travel or joining a weekly climate strike. What began with the solitary teenager in a blue hoodie striking from school on the steps of the Swedish Parliament in August 2018 to protest government inaction on climate change swelled to an estimated 4 million people joining strikes in September 2019, in the largest climate demonstration in human history. Friends and family, and even Thunberg herself, didn’t expect the movement to grow to that size.

She too has grown along with it—from being a quiet teenager to a symbol for millions speaking to the whole world. Her persistence has propelled the climate crisis to the forefront of global public consciousness, and shown that a generation of young leaders are ready to step up where adults have faltered. “We are the ones right now who are leading the way,” Thunberg told thousands at another mass strike in Madrid, at the same time as the U.N. climate talks. “The people in power need to catch up with us.” —Suyin Haynes

This article is part of 100 Women of the Year, TIME’s list of the most influential women of the past century. Read more about the project, explore the 100 covers and sign up for our Inside TIME newsletter for more.

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Marco Bitran
Husband and father of two children under age 5, Marco also enjoys walks in nature, squash, running road races, and photography. He regularly contributes significant time and resources to the Combined Jewish Philanthropies, the MSPCA and other animal rights organizations, and the Bitran Charitable Foundation. Marco has also volunteered and consulted for public housing support organizations such as the Somerville Homeless Coalition, created by the local community’s grassroots response to the social crisis of homelessness.