Cotillard was the ambassador of "1 Heart 1 Tree", an art project that fights climate change through its "Plant for the Planet" reforestation program. On 29 November 2015, The Eiffel Tower became a virtual forest with trees and words encouraging environmental activism projected onto it every evening. Cotillard and UN Secretary General Ban Ki-Moon, inaugurated the light installation on the eve of the official opening of the COP21 conference. She also donated her shoes to be displayed among an installation of over 10,000 shoes at the Place de la Republique in Paris. The installation replaced a giant march for climate change which was forbidden by French authorities following the deadly attacks in the capital on 13 November, which cost 130 lives. It was a way of showing the determination of protesters in their fight against climate change, and allowed them to still send a strong message on the eve of the U.N. climate conference (COP21).