The national framework is particularly important for setting the pricing signals to discourage environmental externalities, such as greenhouse gas emissions. A strong national framework based on a carbon tax or price will broaden the range of environmentally effective options available to cities. If national policy settings are not supportive, some seemingly desirable city-level initiatives may have limited effect or even generate perverse outcomes. With a strong national framework in place, much can often still be done most efficiently at the level of regions or cities. For example, policies to ensure adequate skills in making existing buildings more energy efficient or for encouraging clusters of green industry are probably best designed at city level. Even if there is a national framework in place, there must still be considerable scope for place-specific adaptations, since information about local conditions can be crucial to the effectiveness of such efforts.