| 英文摘要: | Negotiating reductions in greenhouse gas emission involves the allocation of emissions and of emission reductions to specific agents, and notably, within the current UN framework, to associated countries. As production takes place in supply chains, increasingly extending over several countries, there are various options available in which emissions originating from one and the same activity may be attributed to different agents along the supply chain and thus to different countries. In this way, several distinct types of national carbon accounts can be constructed. We argue that these accounts will typically differ in the information they provide to individual countries on the effects their actions have on global emissions; and they may also, to varying degrees, prove useful in supporting the pursuit of an effective and just climate policy. None of the accounting systems, however, prove 'best' in achieving these aims under real-world circumstances; we thus suggest compiling reliable data to aid in the consistent calculation of multiple carbon accounts on a global level.
The current UN emission allocation system for greenhouse gases (GHG) attributes emissions to that country in which emissions physically occur during production (production-based principle)1. Three core alternative forms of emission accounting principles have been proposed in the literature. First, irrespective of where they emerge in the supply chain, emissions could be attributed to the country that extracts the fossil fuels that allow for these emissions (extraction-based principle)2. Second, one could acknowledge that factors other than fossil fuels, such as labour and capital, also benefit from a polluting production process by earning income (wages, interest, rents). Thus, all emissions discharged along the supply chain could be attributed to specific agents (and countries) according to the value they add in production, and thus according to the income they earn (income-based principle, also known as 'enabled' emissions or downstream responsibility)3, 4. Finally, emissions occurring in the production process may also be attributed to the very end of the supply chain, that is, to the consumers (or more precisely: the final users) and their country of residence (consumption-based principle, upstream responsibility)5, 6. As shown in Fig. 1, the global distribution of per capita GHG emissions varies considerably depending on which of these four principles is employed.
The advantages and disadvantages of the adoption of each of the four accounting principles crucially depend on the economic and institutional implementation environment. To provide a point of reference, we first analyse an idealized setting, considered 'first-best' by neoclassical economists. If markets are complete and fully competitive, and if climate policy (i) covers all GHG emissions globally and (ii) imposes (at least implicitly) a globally uniform (shadow) price on each type of GHG (which, if it equals marginal damages, additionally ensures overall efficiency), then environmental and cost-effectiveness are guaranteed irrespective of which accounting system is chosen, that is, irrespective of where in the supply chain (extractor, producer, income beneficiary or consumer) the targets are set and the instruments are applied. In such a setting, markets pass on the incentives fully to all other agents in the supply chain, both upstream and downstream. In a similar fashion, all the burdens and benefits of the policy are also passed on. To which agent they accrue depends only on the elasticities of supply and demand for goods and primary inputs, but not on the accounting system. Thus, theoretically, the same international distribution of income can be achieved irrespective of which of the four accounting systems (and corresponding policies) is chosen. This, however, requires that — for example, if climate policy is negotiated by means of the allocation of GHG emission rights — country endowments are set accordingly; for instance, countries can be endowed with production-based emission permits or a corresponding amount of extraction-based emission permits. Political feasibility may, however, require a different allocation: extraction-based permits might be distributed only to extracting countries if an extraction-based accounting principle is introduced, for example, whereas under a production-based system permits might only go to countries hosting emitting industries. Thus, the choice of a particular accounting system may also have distributional implications.
Reality is characterized neither by complete and fully competitive markets nor by the near-term possibility of implementing a climate policy that encompasses all GHG emissions globally and that results at least implicitly in a uniform CO2 equivalent (CO2e) price across all GHGs and countries. In such a 'second-best' world, climate policies pursued by individual countries or 'coalitions of the willing' are (globally) less environmental and cost-effective than in a 'first-best' world. How much effectiveness is lost typically depends on the particular accounting system choice (and the associated policies)URL: | http://www.nature.com/nclimate/journal/v6/n1/full/nclimate2867.html
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