اشکالاتی و فرصت های اتهامات عنوان شده علیه کربن در مناطق شهری - رویکرد فضایی تعادل عمومی

In cities there is a variety of economic and spatial forces that may influence to what extent a travel-related CO2 emission pricing can be an effective instrument to contribute to the achievement of CO2 reduction goals. Therefore, we examine the effectiveness and impact of CO2 emission charges using a spatial general equilibrium model of an urban economy, calibrated according to an average German city. Our analyses suggest that the imposition of a Pigouvian type CO2 emission charge on urban passenger travel may be able to reduce emissions by about 1%–11%, depending on the estimated social damage cost of carbon dioxide. Such a policy increases urban welfare mainly on account of a reduction of congestion costs. However, pricing congestion directly not only provides higher urban welfare but also higher emission reductions. Pricing congestion and CO2 emissions simultaneously allows to achieve a wide range of emission reduction goals. If, however, the reduction goal is very ambitious the emission charge must be raised to higher levels. Then, distortions in the urban markets and in spatial travel decisions lower labor supply and thus urban production, income of city residents, federal tax revenue, income of landowners outside the city, all together implying losses in welfare.

A CO2 emission tax is a market based economic instrument to internalize climate change effects induced by greenhouse gas (GHG) emissions (see e.g. Poterba, 1993 and Baranzini et al., 2000). Levying such a tax on travel-related CO2 emissions induces effects similar to those imposed by a gasoline tax which is extensively examined in a second-best setting (see e.g. Parry and Small, 2005). Within an urban economy further effects usually not considered accrue on account of spatial location decisions. The increase in the cost of travel implies relocations such that the length of travel trips declines. This might also affect congestion. Moreover, the availability of alternative transport modes may result in a choice of less GHG intensive modes implying less automobile trips and so a potential to curb congestion. However, the benefits from the accessibility of centrally located land areas and the scarcity of land in those areas restrict the power of such an instrument. Therefore, residential, employment as well as shopping locations are spread across the urban area making travel activities essential. As a consequence, there is a variety of forces that may influence whether travel-related emission pricing can actually be both an effective instrument to contribute to the achievement of CO2 emission reduction goals within a metropolitan area and an instrument to improve welfare in this area. This is our point of departure. We examine the power of CO2 emission charges for achieving different CO2 emission reduction levels2 in urban passenger transport and explore the impact of these charges on the city and its residents. The automobile emission charge we derive consists of two components: a tax which is proportional to individual CO2 emissions (and thus gasoline consumption) and a route dependent toll component which explicitly takes into account the interaction between congestion, gasoline consumption and emissions. This second component constitutes a price on the emission externality, i.e. on marginal external CO2 emissions of others caused by one's decision to travel by automobile.3 However, on account of the similarity of this externality to a congestion externality we also consider the interplay between a congestion toll and the emission charge. Examining this issue is significant because more than 73% of the population of OECD countries lives in urban areas (World Bank, 2008) which are, thus, the center of private activities of the majority of people. This includes the emission of GHG by transport, production and housing. Although GHG emissions decline with urban density (see e.g. Newman, 2006, Brownstone & Golob, 2009 and Glaeser & Kahn, 2010), traffic related activities in agglomerations are a major source of such emissions. For example, in London transportation activities cause 22% and in Barcelona 35% of all CO2 emissions of the respective city (Dodman, 2009 and Satterthwaite, 2008). In the European Union (EU) CO2 emissions from the road sector were by about 30% higher than in 1990 and accounted for 71% of total emissions from transport (besides railway and civil aviation) in 2006. Moreover, transport as a whole is the only sector of the European economy where emissions are predicted to increase in the future (European Commission, 2008). To address these issues we employ a spatial computable general equilibrium model of an urban economy calibrated to an average German metropolitan area. As far as we know, this is the first time that such an approach is applied to CO2 emissions. In this regard, our analysis is, to the best of our knowledge, the first modeling framework that deals systematically with the relationship between spatial structure, transport, climate change and economics in a spatial urban model.4 This approach allows to offer more specific insights into the performance of the various instruments for the purpose of combating global warming as postulated by Grazi and van den Bergh (2008). Most computable general equilibrium (CGE) models considering transportation focus on congestion costs and tolls imposed to internalize external time delays (e.g. Anas & Xu, 1999, Anas & Rhee, 2006 and Conrad & Heng, 2002), though there are papers on carbon taxes (e.g. Berg, 2007 and Böhringer & Rutherford, 2002), other environmental taxes (e.g. Bovenberg & Goulder, 1996 and Böhringer & Rutherford, 2002), or emission allowances (e.g. Böhringer and Rosendahl, 2009). However, a spatial equilibrium is not implemented in most CGE studies except for Anas & Xu, 1999 and Anas & Rhee, 2006. Moreover, as far as carbon taxes are considered these studies do usually not consider congestion-related externalities. In contrast, we derive a CO2 emission charge by applying the marginal cost principle on an empirically derived emission function where the charge level is endogenous and may vary across urban space depending on spatially differentiated traffic which is endogenous as well. According to our simulations levying a pure Pigouvian type CO2 emission charge may reduce urban passenger traffic related emissions by about 1–11% depending on the assumed social damage costs of CO2. In addition, such a policy increases urban welfare, even if emission charge revenues are not used to cut other distortionary taxes such as labor taxes. This result contrasts with the standard outcome that environmental taxes cause a welfare decline. Though there might be a double dividend (Pearce, 1991) in the labor market which implies an opposite force to the negative effects of higher transport or energy taxation it is usually too weak to offset welfare losses induced by higher transport or energy costs and the interaction with other distortionary taxes (see Jorgenson & Wilcoxen, 1993, Bovenberg & De Mooji, 1994, Goulder, 1995 and Berg, 2007). The main reason for our results is that we also consider congestion externalities. In this case the emission charge causes positive side-effects on congestion (see also Parry and Bento, 2002). However, we also find that implementing a congestion toll imposed in order to internalize costs associated with congestion-related automobile travel time delays is a more efficient instrument in various respects, even the reduction of travel-related CO2 emissions. Imposing both levies an emission charge and a congestion toll simultaneously at a Pigouvian level reduces CO2 emissions by about 19–21% depending on the damage cost of carbon dioxide and raises urban welfare (but not non-urban welfare). Increasing the emission charge level in order to realize more ambitious emission reduction goals causes stronger distortions in the urban markets and in spatial travel decisions. This lowers labor supply, urban production, income of city residents, federal tax revenue and income of landowners outside the city, all together implying welfare losses. As a consequence, a very ambitious climate-related policy based on additional CO2 emission charges on traffic related emissions may become harmful for residents. The paper is organized as follows: in Section 2 we present the main features of the spatial model. Section 3 describes the model calibration and some results of the initial benchmark simulation. In Section 4 we analyze the impacts of different urban travel-related pricing policies. Particularly, we discuss effects regarding changes in emissions, location decisions, the spatial distribution of economic activity and welfare. Section 5 concludes and gives some suggestions to further research.

Since policies aiming at reducing transport related CO2 emissions strongly affect cities we examine the impact of a CO2 emission charge levied on passenger transport on an urban economy. Our spatial general equilibrium approach allows to consider location decisions, endogenous congestion, Pigouvian charge levels and feedback effects on urban markets. As far as we know, this is the first study where CO2 emissions and congestion are both considered in such a framework. We have found that Pigouvian emission charges are an effective device to achieve moderate emission reduction goals when considering spatial interdependencies. Moreover, from the perspective of city residents, the emission charge is a welfare enhancing instrument except for very high levels of the charge. The main reasons for this outcome are efficiency gains accruing from the reduction in congestion costs which are, however, decreasing with a raise in the charge level. Hence, there is a dividend of an emission charge which does not work via the labor market through cuts in other distortionary taxes but through the interactions with congestion. Because the emission charge we derived contains a component focusing on traffic congestion, we also analyzed the impacts of imposing a pure congestion toll. The simulations show that a pure congestion toll is a more efficient instrument in various respects, even the reduction of passenger travel-related CO2 emissions. However, implementing only emission taxes which might be more attractive for policymakers is less effective. Examining a simultaneous imposition of a congestion toll and emission charge shows that a wide range of emission reduction goals can be achieved, but in the case of higher reduction goals only at the expense of welfare. These results imply that travel-related pricing instruments may indeed contribute to achieve moderate emission reduction goals. One should however bear in mind that we only considered congestion tolls, emission charges and emission taxes. Because of the high welfare costs of the emission charge in the case of very ambitious reduction goals other policies should be explored. Here, one can think of technological developments in improving fuel economy or technical rules for automobiles. In addition we did not consider revenue recycling through cuts in other distortionary taxes (Parry and Bento, 2001) and, thus, not exploit all possible sources of welfare gains associated with emission charges.