Climate Impact Response Functions as Impact Tools in the Tolerable Windows Approach

A critical issue for policymakers in defining mitigationstrategies for climate change is the availability ofappropriate evaluation tools. The development of climate impactresponse functions (CIRFs) is our reaction to this challenge.CIRFs depict the response of selected climate-sensitive impactsectors across a wide range of plausible futures. They consist ofa limited number of climate-change-related dimensions andsensitivities of sector-specific impact models. The concept ofCIRFs is defined and the procedure to develop them is presented.The use of climate change scenarios derived from various GCMexperiments and the adopted impact assessment models areexplained.The CIRFs presented here consider climate change impacts onnatural vegetation, crop production, and water availability. Theyare part of the ICLIPS integrated assessment framework based onthe tolerable windows approach. CIRFs can be applied both in`forward' and in `inverse' mode. In the latter, they help totranslate thresholds for climate impacts perceived by stakeholders(so-called impact guardrails) into constraints for climatevariables (so-called climate windows). This enables the results ofdetailed impact models to be incorporated into intertemporallyoptimizing integrated assessment models, such as the ICLIPS model.     

Climate Protection Strategies: International Allocation and Distribution Effects

In international climate policy discussions, one of the centralissues for medium- to long run climate protection strategiesis the uncertainty about the costs and the distributional effectsof specific unilateral or multilateral emission reductions. Thispaper looks at the world-wide effects of climate protection strategieson the allocation of resources, on economic growth in differentregions, and on the regional welfare effects. The analysis isbased on a global recursively dynamic, multi-region, multi-sectorcomputable general equilibrium model parameterized accordingto the ICLIPS (Integrated Assessment of Climate Protection Strategies)integrated assessment model. The simulations show that nationalclimate policies will have important international repercussions.It is therefore important to consider international allocationeffects in the analysis of national climate protection strategies.The welfare costs of greenhouse gas emission reductions risemore than proportionally with lower emission targets. The analysisof the carbon leakage rate indicates that most of the leakagerapidly disappears if emission reduction moves towards an efficientdistribution of emission targets.     

Economic Development and Emission Control over the Long Term: The ICLIPS Aggregated Economic Model

In integrated assessments of climate change, greenhouse-gasemissions and climate change impacts provide the linkages betweenthe world economy and the climate system. Key climatic processesoperate at the scales of centuries. This requires highlyaggregated models for portraying the dynamics of the economicsystem. An extended Ramsey-type optimal growth model is presentedas the appropriate tool to be integrated with a reduced-formclimate model in the ICLIPS integrated assessment. Theeleven-region model of the world economy involves exogenouspopulation and endogenous investment dynamics with productivityprogress based on a technological diffusion model. World regionsare linked via intertemporal trade flows of the compositeconsumption/investment good, capital mobility, and emission permittrading. Coupled with the ICLIPS Climate Model, the AggregatedEconomic Model can determine corridors of permitted long-termcarbon emission paths or, as primarily discussed in this paper,specific cost-effective emission trajectories. The sensitivity ofmitigation costs to externally specified climate change/impactconstraints and to assumptions about non-CO₂ greenhouse-gasemissions is also discussed.     

Integrated assessment modelling as a positive science: private passenger road transport policies to meet a climate target well below 2 <Superscript>∘</Superscript>C

Transport generates a large and growing component of global greenhouse gas emissions contributing to climate change. Effective transport emissions reduction policies are needed in order to reach a climate target well below 2 ^°C. Representations of technology evolution in current integrated assessment models (IAM) make use of systems optimisations that may not always provide sufficient insight on consumer response to realistic policy packages for extensive use in policy-making. Here, we introduce FTT: transport, an evolutionary technology diffusion simulation model for road transport technology, as an IAM sub-component, which features sufficiently realistic features of consumers and of existing technological trajectories that enables to simulate the impact of detailed climate policies in private passenger road transport. Integrated to the simulation-based macroeconometric IAM E3ME-FTT, a plausible scenario of transport decarbonisation is given, defined by a detailed transport policy package, that reaches sufficient emissions reductions to achieve the 2 ^°C target of the Paris Agreement.     

Confronting the challenge of integrated assessment of climate adaptation: a conceptual framework

Key limitations of integrated assessment models (IAMs) are their highly stylized and aggregated representation of climate damages and associated economic responses, as well as the omission of specific investments related to climate change adaptation. This paper proposes a framework for modeling climate impacts and adaptation that clarifies the relevant research issues and provides a template for making improvements. We identify five desirable characteristics of an ideal integrated assessment modeling platform, which we elaborate into a conceptual model that distinguishes three different classes of adaptation-related activities. Based on these elements we specify an impacts- and adaptation-centric IAM, whose optimality conditions are used to highlight the types of functional relationships necessary for realistic representations of adaptation-related decisions, the specific mechanisms by which these responses can be incorporated into IAMs, and the ways in which the inclusion of adaptation is likely to affect the simulations’ results.     

气候变化综合评估模型的损失函数研究进展

该研究从综合评估模型(IAM)的模型耦合视角出发,介绍了当前损失函数的研究进展,主要从损失函数的构建方法、损失函数与IAM气候模块和经济模块的耦合以及IAM与气候模式的耦合角度分析了损失函数的耦合功能及其存在的科学问题,探讨了损失函数的改进方向。通过文献梳理发现,损失函数的构建方法上,主要采用专家判断法、元分析法和统计学方法,但各有优缺点;与气候模式的耦合功能上,损失函数多以温升为气候变化因素,降水等气候变化信息无法表达,且由全球尺度的年平均值进行标定,不能体现区域的差异和季节的变化,无法直接描述极端气候事件造成的巨大损失;与经济模块的耦合功能上,基于生产部门的损失函数缺乏间接损失评估功能,缺乏对经济增长的动态影响机制。针对上述IAM中气候变化对经济影响的反馈机制的不足,需重点从细化区域气候变化因素影响和细分经济产业部门两个方向重构损失函数,紧密连接气候模式与经济模块,全面评估气候变化经济损失,并需要从技术上解决损失函数在耦合经济模块与气候模式时出现的时空尺度不匹配问题,最终为IAM与气候模式甚至地球系统模式的耦合提供重要的解决方案。     

对地球系统模式与综合评估模型双向耦合问题的探讨

概述了地球系统模式和综合评估模型在研究人类活动与气候变化问题上的优势和劣势,明确了将二者进行双向耦合的必要性,客观分析了综合评估模型耦合过程中存在的主要问题,同时系统总结了国际和国内解决耦合难点的主要方法和最新进展,最后分析和讨论了双向耦合模式的不确定性来源和解决方法,为我国进行地球系统模式与综合评估模型双向耦合提供新思路和方法。     

Methodological Aspects of the Tolerable Windows Approach

The tolerable windows approach (TWA) allows the climate policyformulation process to be safeguarded in the following way. First,guardrails are defined in order to exclude intolerable climatechange impacts, on the one hand, and unacceptable socioeconomicconsequences of climate change mitigation measures, on the other.Second, a scientific analysis is conducted to investigate thefeatures of those emission paths that are compatible with theguardrail constraints. The fundamental methodology of the TWA isbest described in terms of the theory of differentialinclusions. This emerging mathematical theory already providesnumerical methods applicable as long as the underlying integratedassessment models are of limited complexity. In order to identifyemissions corridors, we propose a novel calculation schemeapplicable also for large-scale integrated assessment models.     

Modeling Agriculture and Land Use in an Integrated Assessment Framework

The Agriculture and Land Use (AgLU) model is a top-downeconomic model with just enough structure to simulate globalland-use change and the resulting carbon emissions over one century.These simulations are done with and without a carbon policy representedby a positive carbon price. Increases in the carbon price createincentives for production of commercial biomass that affect thedistribution of other land types and, therefore, carbon emissionsfrom land-use change. Commercial biomass provides a link betweenthe agricultural and energy systems. The Integrated Assessmentof Climate Protection Strategies (ICLIPS) core model uses AgLUto provide estimates of carbon emissions from land-use changeas one component of total greenhouse gas emissions. Each majorland-use type is assigned an average carbon density used to calculatea total carbon stock; carbon emissions from land-use change arecalculated as the change in carbon stock between time periods.Significant carbon emissions from land-use change are presenteven in the reference scenario. An aggressive ICLIPS mitigationscenario results in carbon emissions from land-use change upto 800 million metric tons per year above the AgLU referencescenario.     

Why regional studies are needed in the development of full-scale integrated assessment modelling of global change processes

Full-scale integrated assessment models (lAMs) allow many components of the global climate change problem to be examined in one framework. The chief advantage of the IAM approach over less complete modelling frameworks is that the socio-economic and environmental consequences of policy choices aimed at abating or adapting to climate change can be evaluated in their totality. However, the highly aggregate functional forms that lAMs currently embed are lacking in sufficient regional and sectoral detail to be totally credible. In this paper, ten reasons why regional studies are needed in support of the development of full-scale lAMs are given. A strategic cyclical scaling exercise involving regional and global integrated modelling frameworks is proposed.     

Integrated Assessment of Long-term Climate Policies: Part 2 – Model Results and Uncertainty Analysis

An integrated assessment model (IAM) is applied to explore optionsfor long-term climate policy by identifying permitted emissioncorridors. The options are determined under various assumptionsabout constraints related to acceptable impacts of climate changein terms of alterations induced in natural ecosystems in protectedareas and about acceptable mitigation costs, burden sharingprinciples, and implementation flexibility. The results show thatabout 25% of the protected areas worldwide will witness ecosystemtransformation in the next century even if the costs of emissionreduction are allowed to reach 2% of per-capita consumption. Anuncertainty analysis surveys the implications of modifyingselected key model variables on the existence and shape of theemission corridors. Within plausible ranges of parametervariations, the emission corridor turns out to be rather sensitiveto impact constraints, climatic constraints like the magnitude andrate of the global mean temperature increase, and to aerosolemission scenarios.     

近50年中国风速变化多气候模式模拟检验

近年来,随着气候模式研究的快速发展,全球气候模式在模拟20世纪气候和气候变化特征,尤其是在模拟温度、降水等要素特征和变化及其人类活动对这些要素的影响等方面取得了丰硕的成果.然而,全球气候模式对近地层风速的模拟情况如何,目前仍缺少分析和检验.本文利用中国区域近地层风速观测资料,检验评估了参与IPCC AR4"20世纪气候耦合模式模拟"(20C3M)的19个伞球气候模式和国家气候中心新一代伞球气候模式(BCC_CSM1.0.1)模拟的1956-1999年中国近地层(10m)风速及其变化的模拟能力.研究发现,20个伞球气候模式基本上都能模拟出中国多年年(或季)平均风速分布状况,但模式模拟的平均风速一般小于观测值,尤以观测风速较大的北部和西北部地区模拟值偏小显著.气候模式模拟秋冬季风速分布的能力强于模拟夏春季的能力.模式基本上能模拟出冬、春季平均风速大于夏、秋季平均风速,但是模拟不出春、冬、夏、秋季平均风速依次减小的季节变化特征.模式及模式集成难以模拟出观测到的近50年中国年(或季)平均风速明显减小的变化趋势,少数模式能模拟出年(或季)平均风速略呈减小的变化趋势,但与观测值比相差约一个量级.模式对北部和西南部地区平均风速的变化模拟效果较好,而模式难以模拟东南-南部地区风速变化特征.     

Integrated assessment of abrupt climatic changes

One of the most controversial conclusions to emerge from many of the first generation of integrated assessment models (IAMs) of climate policy was the perceived economic optimality of negligible near-term abatement of greenhouse gases. Typically, such studies were conducted using smoothly varying climate change scenarios or impact responses. Abrupt changes observed in the climatic record and documented in current models could substantially alter the stringency of economically optimal IAM policies. Such abrupt climatic changes — or consequent impacts — would be less foreseeable and provide less time to adapt, and thus would have far greater economic or environmental impacts than gradual warming. We extend conventional, smooth IAM analysis by coupling a climate model capable of one type of abrupt change to a well-established energy–economy model (DICE). We compare the DICE optimal policy using the standard climate sub-model to our version that allows for abrupt change — and consequent enhanced climate damage — through changes in the strength (and possible collapse) of the North Atlantic thermohaline circulation (THC). We confirm the potential significance of abrupt climate change to economically optimal IAM policies, thus calling into question all previous work neglecting such possibilities — at the least for the wide ranges of relevant social and climate system parameters we consider. In addition, we obtain an emergent property of our coupled social–natural system model: “optimal policies” that do consider abrupt changes may, under relatively low discount rates, calculate emission control levels sufficient to avoid significant abrupt change, whereas “optimal policies” disregarding abrupt change would not prevent this non-linear event. However, there is a threshold in discount rate above which the present value of future damages is so low that even very large enhanced damages in the 22nd century, when a significant abrupt change such as a THC collapse would be most likely to occur, do not increase optimal control levels sufficiently to prevent such a collapse. Thus, any models not accounting for potential abrupt non-linear behavior and its interaction with the discounting formulation are likely to miss an important set of possibilities relevant to the climate policy debate.     

Organizational Structure and the Behavior of Firms: Implications for Integrated Assessment

Existing climate/economy models typically treatproduction through the assumptions that firms maximizeprofits and that inputs are transformed to outputsaccording to a neoclassical production function. Yetthese assumptions are at variance with some of theknown empirical features of business behavior. One ofthe most promising ways to model firms morerealistically is to include organizational networkstructure as an integral part of the representation. The firm's optimization problem then includes not onlythe choice of inputs and outputs, but the choice of anorganizational structure as well. This approach makesit possible to examine in a unified framework a numberof issues pertaining to the internal workings of thefirm: the consequences of multiple organizationalobjectives, the possible existence of productivityspillovers from one activity to another, and thealgorithmic characteristics of procedural routines. Understanding how organizational structures influenceoverall performance is an important step towardsbetter representing firms in integrated assessmentmodels. Our results show that phenomena of the typecharacterizing the `Porter hypothesis' (improvedenvironmental performance without reduction inproductivity or profitability) can appear even in verysimple models of the firm, provided the effects oforganizational structure are taken into account.     

Water Resources Planning and Climate Change Assessment Methods

This paper, which provides background for other papers in the volume, first reviews the nature and development of water resources planning and evaluation criteria at the Federal level in the United States. These criteria constitute a highly developed, complex set of guidelines for project planning and evaluation. The level of development of these criteria and their long historical development from theoretical foundations must be taken into account in relating global climate change to possible changes in planning criteria. Second, the essentials of water project planning and evaluation, including benefit-cost principles and more complex concepts of social decision-making, are outlined. Third, the paper provides an overview of global climate change assessment methods, including impact assessment and integrated assessment. Impact assessment uses a relatively straightforward comparison of with and without situations; integrated assessment attempts to improve on impact assessment by developing more complex models that incorporate a range of feedbacks and interrelationships.     

Improved confidence in regional climate model simulations of precipitation evaluated using drought statistics from the ENSEMBLES models

An ensemble of regional climate model simulations from the European framework project ENSEMBLES is compared with observations of low precipitation events across a number of European regions. We characterize precipitation deficits in terms of two drought indices, the Standardized Precipitation Index and the self-calibrated Palmer Drought Severity Index. Models that robustly describe the observations for the period 1961–2000 in given regions are identified and an assessment of the overall performance of the ensemble is provided. The results show that in general, models capture the most severe drought events and that the ensemble mean model also performs well. Some regions that appear to be more problematic to simulate well are also identified. These are relatively small regions and have rather complex topographical features. The analysis suggests that assessment of future drought occurrence based on climate change experiments in general would appear to be robust. But due to the heterogeneous and often fine-scaled structure of drought occurrence, quantitative results should be used with great care, particularly in regions with complex terrain and limited information about past drought occurrence.