This is a truly beautiful thing that everyone participate with this piece of work. The DDB China cleverly blends the concept of "carbon footprint" with the act of pedestrian crossing. The innocent pedestrians walked unwittingly on a big canvas and left their green footprint on branches of a tree. This concept is contracting our unwitting behaviours which caused greenhouse gas (GHG) emissions, reminding us it's everyone's responsibilities to reduce wastes and cultivate a eco-mind and culture.