Line a large baking sheet with aluminum foil and butter the foil well. Sift the ginger with the baking soda into a small bowl.
In a heavy, medium saucepan, combine the sugar with the corn syrup and water and cook over moderate heat, stirring, just until the sugar dissolves. Bring to a boil and cook over moderate heat until the syrup is a pale honey color and registers 310° (hard-crack stage) on a candy thermometer. Remove the syrup from the heat. Using a long-handled wooden spoon, stir in the nuts, then carefully stir in the ginger mixture. Immediately pour the caramel onto the prepared baking sheet and spread the nuts. Let cool completely, then crack into long shards.