What's the Big Idea?

It's the Science Fair, and the second grade is all over it! Some kids are making man-eating robots. Some kids are holding their breath for a very, very long time. Some kids are doing interesting things with vacuum cleaners. The theme, obviously, is global warming. But what should Ivy and Bean do? Something involving explosions? Or ropes? Somethingwith ice cubes? Or maybe . . . maybe something different.