1. Put oven rack in middle position and preheat oven to 350 degrees. Butter 2 large baking sheets.
2. Whisk together the flour, spices, and salt in a bowl.
3. Stir baking soda into warm water in a cup until dissolved, then stir in molasses.
4. Beat together butter and sugar in another bowl with an electric mixer at high speed until pale and fluffy, about 3 minutes.
5. Beat in baking soda mixture until combined well, then beat in flour mixture until just combined (dough will be crumbly but will hold together when rolling balls).
6. Working with half of the dough, roll level teaspoons of dough into balls, arranging them about 2 inches apart on 1 baking sheet.
7. Flatten balls into 1 1/4-inch rounds with tines of a fork, dipping fork in flour to prevent sticking if necessary. Bake cookies until golden brown, 10-12 minutes, then transfer to a rack to cool.
8. Make more cookies with remaining dough on remaining baking sheet in the same manner.
