As a part of Greta Thunberg's School Strike for Climate protest, Foster held weekly climate strikes in front of the White House in Lafayette Square. On September 13, 2019, Thunberg as a part of her trans-American voyage to COP 25 in Santiago, Chile, joined Foster's White House climate strikes which drew thousands to the site. During his time at Harvard University, he held weekly climate strikes on the steps in front of Widener Library with Divest Harvard organizers who called on the university to divest their endowments in the fossil fuel industry. He helped get 186 additional signatures for their petition to Harvard University during his 3 months that summer. After Foster return from Harvard University in late 2019, he was approached by Jane Fonda where he was asked to help found and construct Fire Drill Fridays which was a weekly climate strike held in front of the U.S. Capitol Building.