Modeling adaptation as a flow and stock decision with mitigation

An effective policy response to climate change will include, among other things, investments in lowering greenhouse gas emissions (mitigation), as well as short-term temporary (flow) and long-lived capital-intensive (stock) adaptation to climate change. A critical near-term question is how investments in reducing climate damages should be allocated across these elements of a climate policy portfolio, especially in the face of uncertainty in both future climate damages and also the effectiveness of yet-untested adaptation efforts. We build on recent efforts in DICE-based integrated assessment modeling approaches that include two types of adaptation—short-lived flow spending and long-lived depreciable adaptation stock investments—along with mitigation, and we identify and explore the uncertainties that impact the relative proportions of policies within a response portfolio. We demonstrate that the relative ratio of flow adaptation, stock adaptation, and mitigation depend critically on interactions among: 1) the relative effectiveness in the baseline of stock versus flow adaptation, 2) the degree of substitutability between stock and flow adaptation types, and 3) whether there exist physical limits on the amount of damages that can be reduced by flow-type adaptation investments. The results indicate where more empirical research on adaptation could focus to best inform near-term policy decisions, and provide a first step towards considering near-term policies that are flexible in the face of uncertainty.     

Adaptation,mitigation, and their disharmonious discontents: an essay

The frequently heard call to harmonize adaptation and mitigation policies is well intended and many opportunities exist to realize co-benefits by designing and implementing both in mutually supportive ways. But critical tradeoffs (inadequate conditions, competition among means for implementation, and negative consequences of pursuing both simultaneously) also exist, along with policy disconnects that are shaped by history, sequencing, scale, contextual variables, and controversial climate discourses in the public. To ignore these issues can be expected to undermine a more comprehensive, better integrated climate risk management portfolio. The paper discusses various implications of these tradeoffs between adaptation and mitigation for science and policy.     

Strategies to adapt to an uncertain climate change

Many decisions concerning long-lived investments already need to take into account climate change. But doing so is not easy for at least two reasons. First, due to the rate of climate change, new infrastructure will have to be able to cope with a large range of changing climate conditions, which will make design more difficult and construction more expensive. Second, uncertainty in future climate makes it impossible to directly use the output of a single climate model as an input for infrastructure design, and there are good reasons to think that the needed climate information will not be available soon. Instead of optimizing based on the climate conditions projected by models, therefore, future infrastructure should be made more robust to possible changes in climate conditions. This aim implies that users of climate information must also change their practices and decision-making frameworks, for instance by adapting the uncertainty-management methods they currently apply to exchange rates or R&D outcomes. Five methods are examined: (i) selecting “no-regret” strategies that yield benefits even in absence of climate change; (ii) favouring reversible and flexible options; (iii) buying “safety margins” in new investments; (iv) promoting soft adaptation strategies, including long-term prospective; and (v) reducing decision time horizons. Moreover, it is essential to consider both negative and positive side-effects and externalities of adaptation measures. Adaptation–mitigation interactions also call for integrated design and assessment of adaptation and mitigation policies, which are often developed by distinct communities.     

Does black carbon abatement hamper CO 2 abatement?

Concerns have been raised that near-term black carbon abatement strategies for global warming mitigation would interfere with the longer-term CO₂ abatement efforts. In response, we put forward a “combined target and metric approach”, a theoretical framework, in which the time horizon of the metric is linked to the specific target of the climate policy. In this approach, a shorter time horizon for the metric is justified only when the overall climate policy is tightened; the lower the target level of the climate policy, the earlier the year of the target. Employing a consistent time perspective for the metric and target means that enhanced near-term reduction of short-lived climate forcers does not reduce the importance of the CO₂ abatement, since the overall climate target is stricter.     

Infinite uncertainty,forgotten feedbacks,and cost-benefit analysis of climate policy

Tol (2003) questioned the applicability of expected cost-benefit analysis to global mitigation policy when he found evidence that the uncertainty surrounding estimates of the marginal damage of climate change could be infinite even if total damages were finite. Yohe (2003) suggested that this problem could be alleviated if international development aid were directed at eliminating the source of the problem – climate induced negative growth rates in a few regions along a handful of troublesome scenarios. The hypothesis about adding a second policy lever to the climate policy calculus is shown to hold, though perhaps not as robustly as originally thought. A portfolio of international policies with at least two independent tools can avoid infinite uncertainty on the margins and the associated implications for global mitigation policy at a reasonable price even in the relatively unlikely event that climate change causes negative economic growth in a region or two. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Limitations of integrated assessment models of climate change

The integrated assessment models (IAMs) that economists use to analyze the expected costs and benefits of climate policies frequently suggest that the “optimal” policy is to go slowly and to do relatively little in the near term to reduce greenhouse gas emissions. We trace this finding to the contestable assumptions and limitations of IAMs. For example, they typically discount future impacts from climate change at relatively high rates. This practice may be appropriate for short-term financial decisions but its extension to intergenerational environmental issues rests on several empirically and philosophically controversial hypotheses. IAMs also assign monetary values to the benefits of climate mitigation on the basis of incomplete information and sometimes speculative judgments concerning the monetary worth of human lives and ecosystems, while downplaying scientific uncertainty about the extent of expected damages. In addition, IAMs may exaggerate mitigation costs by failing to reflect the socially determined, path-dependent nature of technical change and ignoring the potential savings from reduced energy utilization and other opportunities for innovation. A better approach to climate policy, drawing on recent research on the economics of uncertainty, would reframe the problem as buying insurance against catastrophic, low-probability events. Policy decisions should be based on a judgment concerning the maximum tolerable increase in temperature and/or carbon dioxide levels given the state of scientific understanding. The appropriate role for economists would then be to determine the least-cost global strategy to achieve that target. While this remains a demanding and complex problem, it is far more tractable and epistemically defensible than the cost-benefit comparisons attempted by most IAMs.     

日本多主体适应气候变化框架机制及对中国的启示——基于法律政策的视角

通过系统梳理日本适应气候变化法律政策的发展历程,分析日本多主体适应气候变化的框架机制,结合其目前具体的适应实践进展,总结出可供中国借鉴的经验启示。研究发现,日本适应气候变化法律政策的发展经历了由重减缓、轻适应,到上升至国家战略,再到立法这3个阶段,形成了以国家、国立环境研究所、地方公共团体、地区气候变化适应中心、企业和居民为主体的多主体适应框架,从科研成果与决策应用转化、适应信息“共享—反馈—更新”有效循环、建立跨地区合作平台、适应资金支持、实施进度监测管理等5个方面构建了多主体适应气候变化机制。目前日本各适应主体逐步开展适应气候变化实践,但适应工作仍处于初期阶段,适应信息共享体系、跨地区合作细则以及适应政策实施效果评价体系有待进一步完善。结合日本的法律政策经验和中国具体情况,提出了中国应科学定位适应气候变化法律地位、加快立法进程,完善“监测评估—信息共享—适应行动—效果评价”多主体适应框架的机制体制,引导企业采取气候风险管理和适应性商业活动,提高居民的适应认知和适应能力的政策建议。     

AD-DICE: an implementation of adaptation in the DICE model

Integrated Assessment Models (IAMS) have helped us over the past decade to understand the interactions between the environment and the economy in the context of climate change. Although it has also long been recognized that adaptation is a powerful and necessary tool to combat the adverse effects of climate change, most IAMS have not explicitly included the option of adaptation in combating climate change. This paper adds to the IAM and climate change literature by explicitly including adaptation in an IAM, thereby making the trade-offs between adaptation and mitigation visible. Specifically, a theoretical framework is created and used to implement adaptation as a decision variable into the DICE model. We use our new AD-DICE model to derive the adaptation cost functions implicit in the DICE model. In our set-up, adaptation and mitigation decisions are separable and AD-DICE can mimic DICE when adaptation is optimal. We find that our specification of the adaptation costs is robust with respect to the mitigation policy scenarios and parameter values. Our numerical results show that adaptation is a powerful option to combat climate change, as it reduces most of the potential costs of climate change in earlier periods, while mitigation does so in later periods.     

What are robust strategies in the face of uncertain climate threshold responses?

We use an integrated assessment model of climate change to analyze how alternative decision-making criteria affect preferred investments into greenhouse gas mitigation, the distribution of outcomes, the robustness of the strategies, and the economic value of information. We define robustness as trading a small decrease in a strategy’s expected performance for a significant increase in a strategy’s performance in the worst cases. Specifically, we modify the Dynamic Integrated model of Climate and the Economy (DICE-07) to include a simple representation of a climate threshold response, parametric uncertainty, structural uncertainty, learning, and different decision-making criteria. Economic analyses of climate change strategies typically adopt the expected utility maximization (EUM) framework. We compare EUM with two decision criteria adopted from the finance literature, namely Limited Degree of Confidence (LDC) and Safety First (SF). Both criteria increase the relative weight of the performance under the worst-case scenarios compared to EUM. We show that the LDC and SF criteria provide a computationally feasible foundation for identifying greenhouse gas mitigation strategies that may prove more robust than those identified by the EUM criterion. More robust strategies show higher near-term investments in emissions abatement. Reducing uncertainty has a higher economic value of information for the LDC and SF decision criteria than for EUM.     

A robust sequential CO2 emissions strategy based on optimal control of atmospheric CO2 concentrations

This paper formally introduces the concept of mitigation as a stochastic control problem. This is illustrated by applying a digital state variable feedback control approach known as Non-Minimum State Space (NMSS) control to the problem of specifying carbon emissions to control atmospheric CO₂ concentrations in the presence of uncertainty. It is shown that the control approach naturally lends itself to integrating both anticipatory and reflexive mitigation strategies within a single unified framework. The framework explicitly considers the closed-loop nature of climate mitigation, and employs a policy orientated optimisation procedure to specify the properties of this closed-loop system. The product of this exercise is a control law that is suitably conditioned to regulate atmospheric CO₂ concentrations through assimilating online information within a 25-year review cycle framework. It is shown that the optimal control law is also robust when faced with significant levels of uncertainty about the functioning of the global carbon cycle.     

The long-term policy context for solar radiation management

We examine the potential role of “solar radiation management” or “sunlight reduction methods” (SRM) in limiting future climate change, focusing on the interplay between SRM deployment and mitigation in the context of uncertainty in climate response. We use a straightforward scenario analysis to show that the policy and physical context determine the potential need, amount, and timing of SRM. SRM techniques, along with a substantial emission reduction policy, would be needed to meet stated policy goals, such as limiting climate change to 2 °C above pre-industrial levels, if the climate sensitivity is high. The SRM levels examined by current modeling studies are much higher than the levels required under an assumption of a consistent long-term policy. We introduce a degree-year metric, which quantifies the magnitude of SRM that would be needed to keep global temperatures under a given threshold.     

A proposal for a new scenario framework to support research and assessment in different climate research communities

In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities.     

Optimal Technology R&D in the Face of Climate Uncertainty

This paper explores optimal near-term technology R&D in the face of uncertain damages caused by the buildup of greenhouse gases. The paper puts particular emphasis on understanding how optimal near-term R&D expenditures might vary based on the technologies pursued in the R&D program. The exploration is conducted in the context of varying impacts from R&D on the global abatement cost function. The R&D planning problem is considered first within a theoretical framework and is then pursued in a stylized application using the DICE model. The paper provides intuition into the circumstances under which near-term technology R&D might increase or decrease under uncertainty, thereby serving as a hedge against climate uncertainty.     

Evaluating the US Mid-Century Strategy for Deep Decarbonization amidst early century uncertainty

The recent change in US presidential administrations has introduced significant uncertainty about both domestic and international policy support for continued reductions in GHG emissions. This brief analysis estimates the potential climate ramifications of changing US leadership, contrasting the Mid-Century Strategy for Deep Decarbonization (MCS) released under the Obama Administration, with campaign statements, early executive actions, and prevailing market conditions to estimate potential emission pathways under the Trump Administration. The analysis highlights areas where GHG reductions are less robust to changing policy conditions, and offers brief recommendations for addressing emissions in the interim. It specifically finds that continued reductions in the electricity sector are less vulnerable to changes in federal policy than those in the built environment and land use sectors. Given the long-lived nature of investments in these latter two sectors, however, opportunities for near-term climate action by willing cities, states, private landowners, and non-profit organizations warrant renewed attention in this time of climate uncertainty.

Key policy insights

• The recent US presidential election has already impacted mitigation goals and practices, injecting considerable uncertainty into domestic and international efforts to address climate change.

• A strategic assessment issued in the final days of the Obama Administration for how to reach long-term climate mitigation objectives provides a baseline from which to gauge potential changes under the Trump Administration.

• Though market trends may continue to foster emission declines in the energy sector, emission reductions in the land use sector and the built environment are subject to considerable uncertainty.

• Regardless of actions to scale back climate mitigation efforts, US emissions are likely to be flat in the coming years. Assuming that emissions remain constant under President Trump and that reductions resume afterwards to meet the Obama Administration mid-century targets in 2050, this near-term pause in reductions yields a difference in total emissions equivalent to 0.3–0.6 years of additional global greenhouse gas emissions, depending on the number of terms served by a Trump Administration.

     

The need for and use of socio-economic scenarios for climate change analysis: A new approach based on shared socio-economic pathways

Socio-economic scenarios constitute an important tool for exploring the long-term consequences of anthropogenic climate change and available response options. A more consistent use of socio-economic scenarios that would allow an integrated perspective on mitigation, adaptation and residual climate impacts remains a major challenge. We assert that the identification of a set of global narratives and socio-economic pathways offering scalability to different regional contexts, a reasonable coverage of key socio-economic dimensions and relevant futures, and a sophisticated approach to separating climate policy from counter-factual “no policy” scenarios would be an important step toward meeting this challenge. To this end, we introduce the concept of “shared socio-economic (reference) pathways”. Sufficient coverage of the relevant socio-economic dimensions may be achieved by locating the pathways along the dimensions of challenges to mitigation and to adaptation. The pathways should be specified in an iterative manner and with close collaboration between integrated assessment modelers and impact, adaptation and vulnerability researchers to assure coverage of key dimensions, sufficient scalability and widespread adoption. They can be used not only as inputs to analyses, but also to collect the results of different climate change analyses in a matrix defined by two dimensions: climate exposure as characterized by a radiative forcing or temperature level and socio-economic development as classified by the pathways. For some applications, socio-economic pathways may have to be augmented by “shared climate policy assumptions” capturing global components of climate policies that some studies may require as inputs. We conclude that the development of shared socio-economic (reference) pathways, and integrated socio-economic scenarios more broadly, is a useful focal point for collaborative efforts between integrated assessment and impact, adaptation and vulnerability researchers.     

Debt-for-climate swaps: Killing two birds with one stone?

The COVID-19 pandemic has further fuelled problems of debt sustainability in developing countries and has sapped the fiscal resources needed to finance climate mitigation and adaptation efforts. We examine whether “debt-for-climate” swaps, instruments whereby debtor countries are relieved from their contractual debt obligations in return for local climate-related spending commitments, may be helpful in tackling worrying debt levels and climate concerns simultaneously. We point out that debt swaps do not have a great historical track record but that common flaws such as their piecemeal nature, lack of additionality and creation of parallel implementation structures, could be overcome by scaling up and careful design. To realize swaps’ full potential, a distinction needs to be made between situations where debt is clearly unsustainable and where it is high but sustainable. In the former case, deep and comprehensive debt restructuring should be the primary focus, rather than closely matching debt service savings with increased climate spending; in the latter case, stand-alone debt swaps may be used to transfer resources from creditors to debtor countries that are committed to climate investments but lack fiscal space. Another helpful differentiation is that between middle-income debtor countries, where debt swaps could finance climate mitigation interventions, and low-income debtors, where investments in adaption deserve prioritization. Finally, debt swap proposals need to be mindful of creditor incentives, including positive reputational payoffs, achieving greater scale using a multi-creditor set-up, at the same time as carefully considering governance credentials in each country context.     

Assessing mitigation-adaptation scenarios for reducing catastrophic climate risk

Countries can use both mitigation and adaptation strategies to protect their citizens from catastrophic risk posed by climate change (e.g., shift in the jet stream). A nation can mitigate by reducing CO₂ emissions, which reduces the probability of a catastrophic event; it can adapt by altering the infrastructure so that damages can be reduced in the event a catastrophe is realized. Herein we add to the current literature by extending the endogenous risk framework into a dynamic framework permitting analysis of both mitigation and adaptation while allowing for the dynamic process of global climate change. Our results suggest adaptation to catastrophe is a small fraction of the national climate protection budget relative to mitigation when nations cooperate fully, when damages are both continuous and catastrophic, and when nations have a short planning horizon. Adaptation becomes more important relative to mitigation when nations are unlikely to cooperate, when damages are mainly catastrophic, or when the nation’s planning horizon increases.     

An updated assessment of the risks from climate change based on research published since the IPCC Fourth Assessment Report

The IPCC Fourth Assessment Report (AR4) published in 2007 presents the most complete and authoritative assessment of the status of scientific knowledge on all aspects of climate change. This paper presents an updated assessment of the risks from anthropogenic climate change, based on a comprehensive review of the pertinent scientific literature published since finalisation of the AR4. Many risks are now assessed as stronger than in the AR4, including the risk of large sea-level rise already in the current century, the amplification of global warming due to biological and geological carbon-cycle feedbacks, a large magnitude of “committed warming” currently concealed by a strong aerosol mask, substantial increases in climate variability and extreme weather events, and the risks to marine ecosystems from climate change and ocean acidification. Some topics remain the subject of intense scientific debate, such as past and future changes in tropical cyclone activity and the risk of large-scale Amazon forest dieback. The rise in greenhouse gas emissions and concentrations has accelerated recently, and it is expected to accelerate further in the absence of targeted policy interventions. Taken together, these findings point to an increased urgency of implementing mitigation policies as well as comprehensive and equitable adaptation policies.     

适应气候变化政策机制的国际经验与启示

中国高度重视适应气候变化工作,实行减缓与适应并重的应对气候变化原则,已出台适应气候变化相关的战略、规划等一系列政策文件。但总体来看,中国适应气候变化政策与行动尚处于起步阶段,面临着法规制度缺位、监测评估不足、组织协调机制不完善等挑战,适应气候变化政策的类型、数量和力度都明显弱于减缓。为完善中国适应气候变化政策与机制的框架设计,文中梳理了相关研究、《联合国气候变化框架公约》下的适应气候变化国际机制及主要国家经验,提出了一套完整闭环的适应气候变化核心决策流程及关键支撑机制,并重点从开展法制建设、制定适应战略（计划）、建立监测评估机制、构建协调机制和完善资金机制等五方面,归纳了主要国家的经验与启示,最终研究提出完善我国适应气候变化政策与机制框架设计的建议,包括加快建立和完善适应气候变化法制建设、加快构建国家适应气候变化的政策体系、加快完善国家适应气候变化的机制设计、加强适应气候变化支撑能力建设、推动适应气候变化的国际合作等。     

Can agriculture support climate change adaptation, greenhouse gas mitigation and rural livelihoods? insights from Kenya

Changes in the agriculture sector are essential to mitigate and adapt to climate change, meet growing food demands, and improve the livelihoods of poor smallholder producers. What agricultural strategies are needed to meet these challenges? To what extent are there synergies among these strategies? This paper examines these issues for smallholder producers in Kenya across several agroecological zones. Several practices emerge as triple wins, supporting climate adaptation, greenhouse gas mitigation, and profitability goals. In particular, integrated soil fertility management and improved livestock feeding are shown to provide multiple benefits across all agroecological zones examined. Triple wins of other agricultural practices are limited to specific agroecological zones. Irrigation and soil and water conservation, for example, are essential for adaptation, mitigation, and profitability in arid areas. The results suggest that agricultural investments targeted toward these triple-win strategies will have the greatest payoff in terms of increased resilience of farm and pastoralist households and global climate change mitigation. To reap the benefits of triple-win strategies will require that policymakers, researchers, and practitioners move away from isolated approaches focused on either adaptation or mitigation or rural income generation toward a more holistic assessment of joint strategies as well as their tradeoffs and synergies.