def load(self, env=None):
        """ Load a section values of given environment.
        If nothing to specified, use environmental variable.
        If unknown environment was specified, warn it on logger.

        :param env: environment key to load in a coercive manner
        :type env: string
        :rtype: dict
        """
        self._load()
        e = env or \
            os.environ.get(RUNNING_MODE_ENVKEY, DEFAULT_RUNNING_MODE)
        if e in self.config:
            return self.config[e]
        logging.warn("Environment '%s' was not found.", e)