Sharks have a tendency to provoke extreme reactions in humans: some of us quiver with fear at the mere thought of a great white, while others celebrate them as the pinnacle of coolness (Shark Week, anyone?). Wherever young environmentalists land on this spectrum, they will be invested in discovering what would happen If Sharks Disappeared (Roaring Brook, $17.99). As Lily Williams sensitively demonstrates in her debut picture book, these impressive creatures are quite literally irreplaceable: without their existence, all life on Earth could be at risk. Williams tempers her sobering topic with a clear focus on what kids can do to help, empowering them with a general sense of hope and a specific list of things they can do to make sure that sharks don’t go anywhere soon. Ages 7-10.