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The literature on metrics to measure contributions to climate change from emissions of different greenhouse gases divides into studies that highlight physical aspects and studies that show the importance of economic factors. This paper distinguishes the physical aspects and implications of economic factors by asking what is demanded from physically based metrics if used for a specific policy objective. We study the aim of maximizing the welfare of emissions generated by consumption when there is a limit to the increase in global mean temperature. In that case, metrics ought to change over time, with increasing weight on short-living gases before the temperature limit is met. Metrics for short-living gases increase also with increasing uncertainty. Adjustments to new information spur higher metrics for short-living gases if it reduces the expected allowable emissions before the target is met, and lower metrics in the opposite case. Under a binding target, metrics refer to the instantaneous impact on radiative forcing multiplied by the lifetime of the respective gases, and adjusted by the attitude to risk. [ABSTRACT FROM AUTHOR]

Economic evaluations of solar radiation management (SRM) usually assume that the temperature will be stabilized, with no economic impacts of climate change, but with possible side-effects. We know from experiments with climate models, however, that unlike emission control the spatial and temporal distributions of temperature, precipitation and wind conditions will change. Hence, SRM may have economic consequences under a stabilization of global mean temperature even if side-effects other than those related to the climatic responses are disregarded. This paper addresses the economic impacts of implementing two SRM technologies; stratospheric sulfur injection and marine cloud brightening. By the use of a computable general equilibrium model, we estimate the economic impacts of climatic responses based on the results from two earth system models, MPI-ESM and NorESM. We find that under a moderately increasing greenhouse-gas concentration path, RCP4.5, the economic benefits of implementing climate engineering are small, and may become negative. Global GDP increases in three of the four experiments and all experiments include regions where the benefits from climate engineering are negative. [ABSTRACT FROM AUTHOR]

Analyses of the costs and benefits of climate policy, such as the Stern Review, evaluate alternative strategies to reduce greenhouse gas emissions by requiring that the cost of emission cuts in each and every year has to be covered by the associated value of avoided damage, discounted by a an exogenously chosen rate. An alternative is to optimize abatement programmes towards a stationary state, where the concentrations of greenhouse gases are stabilized and shadow prices, including the rate of discount, are determined endogenously. This paper examines the properties of optimized stabilization. It turns out that the implications for the evaluation of climate policy are substantial if compared with evaluations of the present value of costs and benefits based on exogenously chosen shadow prices. Comparisons of discounted costs and benefits tend to exaggerate the importance of the choice of discount rate, while ignoring the importance of future abatement costs, which turns out to be essential for the optimal abatement path. Numerical examples suggest that early action may be more beneficial than indicated by comparisons of costs and benefits discounted by a rate chosen on the basis of current observations. [Copyright &y& Elsevier]

Current climate policies are based on the use of Global Warming Potentials (GWPs) to compare emissions of various greenhouse gases. Yet, from an economic point of view, more efficient methods exist. We compare the potential costs of implementing some long-term goal for stabilization of the climate in three cases: Reduce CO2 emissions only, reduce emissions of the four greenhouse gases CO2, CH4, N2O and SF6 using the standard IPCC GWPs and reduce emissions of the same four gases with efficient and flexible, time dependent metrics. A multi-gas approach with GWPs reduces the costs by 8 percent when compared with CO2 reductions only, whereas the costs may be reduced by an additional 2 percent if using flexible metrics. If compared with the use of GWPs, we find that efficient weights increase the cost savings of including non-CO2 gases in climate policy by 15-40%, depending on the stabilization goal. [ABSTRACT FROM AUTHOR]

Adaptation is an important element on the climate change policy agenda. Integrated assessment models, which are key tools to assess climate change policies, have begun to address adaptation, either by including it implicitly in damage cost estimates, or by making it an explicit control variable. We analyze how modelers have chosen to describe adaptation within an integrated framework, and suggest many ways they could improve the treatment of adaptation by considering more of its bottom-up characteristics. Until this happens, we suggest, models may be too optimistic about the net benefits adaptation can provide, and therefore may underestimate the amount of mitigation they judge to be socially optimal. Under some conditions, better modeling of adaptation costs and benefits could have important implications for defining mitigation targets. [ABSTRACT FROM AUTHOR]