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In integrated assessments of climate change, greenhouse-gas emissions and climate change impacts provide the linkages between the world economy and the climate system. Key climatic processes operate at the scales of centuries. This requires highly aggregated models for portraying the dynamics of the economic system. An extended Ramsey-type optimal growth model is presented as the appropriate tool to be integrated with a reduced-form climate model in the ICLIPS integrated assessment. The eleven-region model of the world economy involves exogenous population and endogenous investment dynamics with productivity progress based on a technological diffusion model. World regions are linked via intertemporal trade flows of the composite consumption/investment good, capital mobility, and emission permit trading. Coupled with the ICLIPS Climate Model, the Aggregated Economic Model can determine corridors of permitted long-term carbon emission paths or, as primarily discussed in this paper, specific cost-effective emission trajectories. The sensitivity of mitigation costs to externally specified climate change/impact constraints and to assumptions about non-CO2 greenhouse-gas emissions is also discussed. [ABSTRACT FROM AUTHOR]

The tolerable windows approach (TWA) allows the climate policy formulation process to be safeguarded in the following way. First, guardrails are defined in order to exclude intolerable climate change impacts, on the one hand, and unacceptable socioeconomic consequences of climate change mitigation measures, on the other. Second, a scientific analysis is conducted to investigate the features of those emission paths that are compatible with the guardrail constraints. The fundamental methodology of the TWA is best described in terms of the theory of differential inclusions. This emerging mathematical theory already provides numerical methods applicable as long as the underlying integrated assessment models are of limited complexity. In order to identify emissions corridors, we propose a novel calculation scheme applicable also for large-scale integrated assessment models. [ABSTRACT FROM AUTHOR]

An integrated assessment model (IAM) is applied to explore options for long-term climate policy by identifying permitted emission corridors. The options are determined under various assumptions about constraints related to acceptable impacts of climate change in terms of alterations induced in natural ecosystems in protected areas and about acceptable mitigation costs, burden sharing principles, and implementation flexibility. The results show that about 25% of the protected areas worldwide will witness ecosystem transformation in the next century even if the costs of emission reduction are allowed to reach 2% of per-capita consumption. An uncertainty analysis surveys the implications of modifying selected key model variables on the existence and shape of the emission corridors. Within plausible ranges of parameter variations, the emission corridor turns out to be rather sensitive to impact constraints, climatic constraints like the magnitude and rate of the global mean temperature increase, and to aerosol emission scenarios. [ABSTRACT FROM AUTHOR]

An integrated assessment model (IAM) conceived in the vein of the inverse approach is introduced. The model is designed to help social actors in making informed judgments about climate change impact targets, mitigation costs, and implementation mechanisms. Based on these normative decisions, the model verifies whether there exist long-term future emission paths that satisfy the user-defined constraints. If they do, the model determines an emission corridor containing all permissible emission trajectories. An overview of the IAM is provided and short descriptions of the model components are presented. Forward and inverse modes of application are explained. Examples based on impacts of climate change on aggregated potential crop production in Western Europe and South Asia illustrate how the model can be applied in different modes. The examples demonstrate how the inverse approach separates social judgments shaping climate policy from the model-based analysis of their implications. The examples also show the difference in climate change tolerance between developed regions in temperate zones and less developed regions in already warm climate zones. [ABSTRACT FROM AUTHOR]

The paper introduces the Tolerable Windows Approach (TWA) as a decision analytical framework for addressing global climate change. It is implemented as an integrated assessment model (IAM) developed in the project on Integrated Assessment of Climate Protection Strategies (ICLIPS). The background and the main objectives of the project are described and its relationships to other current integrated assessment efforts are elucidated. Key features of the TWA are compared with those of cost-benefit and cost-effectiveness frameworks. An overview of the ICLIPS IAM framework is provided together with its methodological foundations. Main features of the individual models are presented, covering the climate, the aggregated economic, and the impact models. Additional components of the framework include dynamic mitigation cost functions and an agriculture/land-use model (both incorporated into the fully integrated ICLIPS climate-economy model) as well as a global multi-region, multi-sector, dynamic general equilibrium model. [ABSTRACT FROM AUTHOR]