def warn_land_ocean(*l):
    """Produce a warning about mismatched land/ocean data ranges."""

    def iso8601(x):
        """Produce string of form YYYY-MM."""

        y, m = divmod(x - 1, 12)
        m += 1
        return "%04d-%02d" % (y, m)

    print("WARNING: Bad mix of land and ocean data.\n"
          "  Land range from %s to %s; Ocean range from %s to %s." %
          tuple(map(iso8601, l)))