مالیات انتشار آلودگی داخلی: مدل کلی بهینه سازی نوع تعادل اعمال شده برای ترکیه

This paper presents a modelling attempt to endogenise the level and timing of environmental taxes within an optimisation framework. First, a base model of energy–economy–environmental interactions is extended to allow for exogenous tax analysis. Two types of environmental taxes, one on the sulphur content of fuels and the other on the level of emissions, are exogenously included in the model as alternative instruments to mitigate pollution. Next, the base model is modified to endogenise pollution abatement. This has been achieved by incorporating a preference rate, depending on an index of emissions, into the utility function. Finally, the emission index and emission tax are taken as substitutes and modelled within a CES form to endogenise the emission tax. Results for all cases, obtained with Turkish data, are discussed. It is found that a tax on SO2 emissions is more effective in reducing SO2 emissions than a tax applied on the sulphur content of fuels. It is also found that a gradually increasing tax is more effective in reducing emissions than a constant tax.

Triggered by the commitment to take environmental considerations into account in their social and economic policies and to implement measures for mitigating transboundary air pollution under the 1979 UN Convention, a series of international agreements have focused on SO2 and NOx emission reduction, as for example the 1988 Sofia and 1994 Oslo Protocols, and have proposed a variety of targets and timetables for abatement. The aim of the Sofia Protocol to stabilise NOx emissions at their 1987 level by 1994 has largely been achieved. The Oslo Protocol entered into force in August 1998 and, based on regional emission densities, foresees a 40–80% SO2 emission reduction by the year 2010 relative to emissions in 1980. There exists various measures for reducing pollutant emissions; emission charges, tradable permit systems, environmental taxes, performance bonds, liability payments and non-compliance fees can be stated as some examples. Environmental taxes emerge from the IPCC report (Watson et al., 1996) as potentially effective market instruments and have been suggested as a market-based programme to encourage continued innovation in energy efficient and cleaner technologies. The Commission of the European Communities has suggested in an Information Note on 27 May 1992 (see Nellor, 1997) that environment taxes be used to replace taxes on labour because environment taxes will impose lower social costs boosting economic activity and promoting employment. The environmental effectiveness of taxation, economic effects and associated welfare implications are of primary importance for policy-makers who decide on environmental and economic policies. The international scientific community devotes therefore much research effort to find out about interactions between industrial development and environmental degradation. These interactions are based on an inter-play between key elements of the energy and the economic system like energy consumption patterns, the technological structure and flexibility of the energy system, fuel properties, energy security, capital stock, import composition, foreign exchange availability, household income, available investment capital, etc. The complexity of the interdependencies and the long time scales needed to observe them make it difficult to handle the problem. It is therefore not easy to determine an appropriate tax policy and to measure its impacts. It requires some difficult value judgements as well as a consistent and efficient modelling paradigm capturing energy–economy–environmental three way interactions and including the necessary level of detail in the representation of energy and economic activities.

The reference results indicate that NOx emissions in Turkey remain below the limits set by European standards until 2025 whereas during the same time period SO2 emissions reach levels of about four times higher than those limits. It is found that an imposition of any type of environmental tax to reduce SO2 emissions, whether on the sulphur content of fuels or directly on SO2 emissions, results in a shift away from solid fuels to oil and gas. It is also found that sulphur taxes do not lead to abatement technology installation whereas SO2 emission taxes encourage the instalment of abatement technologies in addition to the change in the energy mix. The most important finding from the exogenous tax analysis is that, in spite of less SO2 reduction, the GDP losses in the sulphur tax scenarios are more than the GDP losses in the SO2 emission tax scenarios. This observation leads to the conclusion that a tax on SO2 emissions is more effective in reducing SO2 emissions than a tax applied on the sulphur content of fuels. Results of the endogenised SO2 emission tax model are in accordance with the exogenous SO2 emission tax results in terms of energy mix, however the shift to oil and gas is more pronounced in the endogenous model. It is observed that the endogenous model initially sets a low tax rate and gradually increases it thereafter. Comparing the economic implications of this tax policy with those of the initially higher stable tax in the exogenous model, it is found that the GDP loss is less in the endogenous SO2 emission tax model than in the exogenous one. In spite of a lower GDP loss, higher reductions in SO2 emissions are observed in the endogenous case. As a result, it is concluded that it is ineffective to apply a high initial tax and hold it stable thereafter instead of a gradually increasing tax policy as suggested by the endogenous tax model. It should be stressed that the introduction of new capabilities into a basic model of energy–economy–environment by the use of a preference rate for emissions and a CES aggregation of 1/tax and emissions has resulted in a more flexible and powerful tool for energy policy analysis and hence made the above policy discussions possible.