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This thesis consists of five papers.

Paper [1] analyzes one possible way of replacing dynamic Pigouvian taxes by a static approximation of such taxes from the point of view of social accounting. The idea is to approximate a Pigouvian emission tax by using the instantaneous marginal willingness to pay to reduce the stock of pollution. If this approximation is close enough to the correct Pigouvian tax it will be useful for at least two reasons: (i) it brings the economy close to the socially optimal solution; and (ii) it provides information relevant for social accounting by closely approximating the value of additions to the stock of pollution.

Paper [2] analyzes the welfare effects of an agreement between countries to slightly increase their emission taxes. The results indicate that such an agreement need not necessarily increase the global welfare level, even if each individual country has set its prereform emission tax to be lower than the marginal social cost of pollution.

Paper [3] provides an economic framework for analyzing the global warming problem, emphasizing the use of forests as a means of carbon sequestration. We explore the difference between the decentralized economy and the socially optimal resource allocation, and discuss the appropriate tax system required to implement the first best optimum.

Paper [4] incorporates the uncertainty involved in the production of nuclear energy into a dynamic general equilibrium growth model. We compare the resource allocation in the decentralized economy with the socially optimal resource allocation and design the dynamic Pigouvian taxes that make the decentralized economy reproduce the socially optimal resource allocation.

Paper [5] treats externalities from nuclear power in a dynamic differential game framework involving two countries, which differ with regard to their nuclear technology. The model is solved numerically, where one country is considered relatively safe and the other relatively less safe.