Supply of carbon sequestration and biodiversity services from Australia's agricultural land under global change

Global agroecosystems can contribute to both climate change mitigation and biodiversity conservation, and market mechanisms provide a highly prospective means of achieving these outcomes. However, the ability of markets to motivate the supply of carbon sequestration and biodiversity services from agricultural land is uncertain, especially given the future changes in environmental, economic, and social drivers. We quantified the potential supply of these services from the intensive agricultural land of Australia from 2013 to 2050 under four global outlooks in response to a carbon price and biodiversity payment scheme. Each global outlook specified emissions pathways, climate, food demand, energy price, and carbon price modeled using the Global Integrated Assessment Model (GIAM). Using a simplified version of the Land Use Trade-Offs (LUTO) model, economic returns to agriculture, carbon plantings, and environmental plantings were calculated each year. The supply of carbon sequestration and biodiversity services was then quantified given potential land use change under each global outlook, and the sensitivity of the results to key parameters was assessed. We found that carbon supply curves were similar across global outlooks. Sharp increases in carbon sequestration supply occurred at carbon prices exceeding 50 $ tCO₂⁻¹ in 2015 and exceeding 65 $ tCO₂⁻¹ in 2050. Based on GIAM-modeled carbon prices, little carbon sequestration was expected at 2015 under any global outlook. However, at 2050 expected carbon supply under each outlook differed markedly, ranging from 0 to 189 MtCO₂ yr⁻¹. Biodiversity services of 3.32% of the maximum may be achieved in 2050 for a 1 $B investment under median scenario settings. We conclude that a carbon market can motivate supply of substantial carbon sequestration but only modest amounts of biodiversity services from agricultural land. A complementary biodiversity payment can synergistically increase the supply of biodiversity services but will not provide much additional carbon sequestration. The results were sensitive to global drivers, especially the carbon price, and the domestic drivers of adoption hurdle rate and agricultural productivity. The results can inform the design of an effective national policy and institutional portfolio addressing the dual objectives of climate change and biodiversity conservation that is robust to future uncertainty in both national and global drivers.     

Incorporating blue carbon sequestration benefits into sub-national climate policies

The emissions reduction pledges made by individual countries through the 2015 Paris Agreement represent the current global commitment to mitigate greenhouse gas emissions in the face of the enduring climate crisis. Natural lands carbon sequestration and storage are critical for successful pathways to global decarbonization (i.e., as a negative emissions technology). Coastal vegetated habitats maintain carbon sequestration rates exceeding forest sequestration rates on a per unit area basis by nearly two orders of magnitude. These blue carbon habitats and their associated carbon sequestration benefits are vulnerable to losses from land-use change and sea-level rise. Incorporation of blue carbon habitats in climate change policy is one strategy for both maintaining these habitats and conserving significant carbon sequestration capabilities. Previous policy assessments have found the potential for incorporation of coastal carbon sequestration in national-level policies, yet there has – to date – been little inclusion of blue carbon in the national-scale implementation of Paris commitments. Recently, sub-national jurisdictions have gained attention as models for pathways to decarbonization. However, few previous studies have examined sub-national level policy opportunities for operationalizing blue carbon into climate decision-making. California is uniquely poised to integrate benefits from blue carbon into its coastal planning and management and its suite of climate mitigation policies. Here, we evaluated legal authorities and policy contexts addressing sequestration specifically from blue carbon habitats. We synthesized the progressive action in California’s approaches to mitigate carbon emissions including statutory, regulatory, and non-regulatory opportunities to incorporate blue carbon ecosystem service information into state- and local-level management decisions. To illustrate how actionable blue carbon information can be produced for use in decision-making, we conducted a spatial analysis of blue carbon sequestration in several locations in California across multiple agencies and management contexts. We found that the average market values of carbon sequestration services in 2100 ranged from $7,730 to $44,000 per hectare and that the social cost of carbon sequestration value was 1.3 to 2.7 times the market value. We also demonstrated that restoration of small areas with high sequestration rates can be comparable to the sequestration of existing marshes. Our results illustrate how accessible information about carbon sequestration in coastal habitats can be directly incorporated into existing policy frameworks at the sub-national scale. The incorporation of blue carbon sequestration benefits into sub-national climate policies can serve as a model for the development of future policy approaches for negative emissions technologies, with consequences for the success of the Paris Agreement and science-based decarbonization by mid-century.     

Integrated estimates of global terrestrial carbon sequestration

Assessing the contribution of terrestrial carbon sequestration to climate change mitigation requires integration across scientific and disciplinary boundaries. A comprehensive analysis incorporating ecologic, geographic and economic data was used to develop terrestrial carbon sequestration estimates for agricultural soil carbon, reforestation and pasture management. These estimates were applied in the MiniCAM integrated assessment model to evaluate mitigation strategies within policy and technology scenarios aimed at achieving atmospheric greenhouse gas stabilization by 2100. Terrestrial sequestration reaches a peak rate of 0.5–0.7 GtC yr⁻¹ in mid-century with contributions from agricultural soils (0.21 GtC yr⁻¹), reforestation (0.31 GtC yr⁻¹) and pasture (0.15 GtC yr⁻¹). Sequestration rates vary over time and with different technology and policy scenarios. The combined contribution of terrestrial sequestration over the next century ranges from 23 to 41 GtC.     

Estimating the value of carbon sequestration ecosystem services in the Mediterranean Sea: An ecological economics approach

Ocean and marine ecosystems provide a range of valuable services to humans, including benefits such as carbon sequestration, whose economic value are as yet poorly understood. This paper presents a novel contribution to the valuation of carbon sequestration services in marine ecosystems with an application to the Mediterranean Sea. We combine a state-of-the-art biogeochemical model with various estimates of the social cost of carbon emissions to provide a spatially explicit characterization of the current flow of values that are attributable to the various sequestration processes, including the biological component. Using conservative estimates of the social cost of carbon, we evaluate the carbon sequestration value flows over the entire basin to range between 127 and 1722 million €/year. Values per unit area range from −135 to 1000 €/km² year, with the exclusive economic zone of some countries acting as net carbon sources. Whereas the contribution of physical processes can be either positive or negative, also depending on the properties of incoming Atlantic water, the contribution of biological processes to the marine “blue carbon” sequestration is always positive, and found to range between 100 to 1500 million €/year for the whole basin.     

The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy

Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate does not, however, weaken the importance of actions that would seek to minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental change and variability.     

Enhancing the sustainability of commodity supply chains in tropical forest and agricultural landscapes

The rapid expansion of the production of agricultural commodities such as beef, cocoa, palm oil, rubber and soybean is associated with high rates of deforestation in tropical forest landscapes. Many state, civil society and market sector actors are engaged in developing and implementing innovative interventions that aim to enhance the sustainability of commodity supply chains by affecting where and how agricultural production occurs, particularly in relation to forests. These interventions – in the form of novel or moderated institutions and policies, incentives, or information and technology – can influence producers directly or achieve their impacts indirectly by influencing consumer, retailer and processor decisions. However, the evidence base for assessing the impacts of these interventions in reducing the negative impacts of commodity agriculture production in tropical forest landscapes remains limited, and there has been little comparative analysis across commodities, cases, and countries. Further, there is little consensus of the governance mechanisms and institutional arrangements that best support such interventions. We develop a framework for analyzing commodity supply chain interventions by different actors across multiple contexts. The framework can be used to comparatively analyze interventions and their impacts on commodity production with respect to the spatial and temporal scales over which they operate, the groups of supply chain actors they affect, and the combinations of mechanisms upon which they depend. We find that the roles of actors in influencing agricultural production depends on their position and influence within the supply chain; that complementary institutions, incentives and information are often combined; and that multi-stakeholder collaborations between different groups of actors are common. We discuss how the framework can be used to characterize different interventions using a common language and structure, to aid planning and analysis of interventions, and to facilitate the evaluation of interventions with respect to their structure and outcomes. Studying the collective experience of multiple interventions across commodities and spatial contexts is necessary to generate more systematic understandings of the impacts of commodity supply chain interventions in forest-agriculture landscapes.     

中国森林乔木林碳储量及其固碳潜力预测

加强对我国森林碳储量和固碳潜力的研究,是制定中国增汇减排政策的重要依据,对我国国际气候谈判和全面了解森林碳汇潜力具有重要作用。利用我国第七次和第八次森林资源清查中各优势树种的面积和蓄积量数据,采用IPCC材积源生物量法（volume-biomass method),估算了我国森林（乔木林）碳储量和碳密度及其分布,分析我国不同省份天然乔木林和人工乔木林碳储量龄组结构特征;建立分区域、分起源主要优势树种的单位面积蓄积-林龄Logistic生长方程,结合我国森林2020年和2030年面积蓄积增长目标,预测我国乔木林2010—2050年间碳汇潜力。结果表明：第八次清查期间中国乔木林总碳储量为6135.68 Tg,碳密度为37.28 Mg/hm ²;天然乔木林和人工乔木林的碳储量分别为5246.07 Tg和889.61 Tg,分别占总碳储量的85.50%和14.50%。到2050年,中国乔木林和新造林的总碳储量和平均碳密度将分别达到11125.76 Tg和52.52 Mg/hm ²,与2010年相比分别增加81%和41%。分析结果表明中国乔木林有很大的碳汇潜力,将在应对和减缓全球气候变化中发挥重要作用。     

主要发达经济体从碳达峰到碳中和的路径及启示

随着气候变化影响加剧,全球气候治理进程加速,实现碳达峰已经成为全球气候行动的核心,各国也相继制定碳中和目标并开展行动。中国在第75届联合国大会一般性辩论上提出了碳达峰碳中和目标,部分已实现碳达峰的发达经济体也提出了各自的碳中和承诺。文中从“整体-阶段”及“焦点-公平”视角分析了欧盟和美国等主要发达经济体碳达峰的历程和特点,以及其碳中和目标和规划。研究发现,发达经济体在碳达峰过程中普遍经历了较长的爬坡期（58~136年）和平台期（4~20年),在碳达峰时,发达经济体的能源结构以油气为主,油气占一次能源消费比重为57%~77%,其人均排放量、历史累计排放以及人均GDP也都处于较高水平,在碳达峰前后总体处于经济与碳排放脱钩状态。各发达经济体的碳中和路径均以能源转型为重点,采用了多元化的政策工具,并且注重低碳和负碳技术的革新。根据发达经济体的政策展望,在实现碳中和时,均难以将绝对排放量降为零,都需要通过碳移除手段进行抵消。通过对比分析,发现中国的碳达峰和碳中和目标是具有雄心的气候承诺,相较其他发达经济体需要付出更大努力。建议运用全面综合的政策工具支撑碳中和目标的有效落实,加快中国的气候立法,在兼顾公正转型的同时推动能源结构调整,注重可再生能源和能效方面的新技术开发应用。     

陆地生态系统固碳速率立体监测方法:进展与挑战

全球CO₂浓度增加造成的全球变暖已成为人类亟需解决的问题,陆地生态系统在过去几十年一直扮演着重要的碳汇角色,吸收了30％左右的人类活动排放CO₂。本文调研分析了陆地生态系统固碳速率空间估算方法,包括样地调查、通量监测、模型模拟、遥感估算等,梳理了各种估算方法的研究现状与进展。样地调查、通量观测等方法可以提供点尺度的固碳速率直接测量信息,但存在观测样本有限、空间代表性不足等问题。模型模拟方法可以从机理的角度描述陆地碳、水、能量循环,模拟预测陆地生态系统固碳速率的状态和变化。然而,在模型建立过程中,抽象和简化会引入结构与假设的不确定性,以及模型驱动数据引入的不确定性等问题是碳循环模型模拟方法面临的重大挑战。卫星遥感具有全球覆盖、分辨率精细、时间序列观测等优点,结合机器学习方法,为地球大数据驱动的全球碳源汇估算提供了新的研究范式。但是,当前各种固碳速率的监测方法还没有满足高度时空异质性的陆地生态系统固碳量监测需求,未来需要整合地面观测、模型模拟和卫星遥感等多种技术手段,提供区域和全球尺度的陆地生态系统碳汇精确估算方法体系和科学数据产品。     

The importance of population,climate change and CO2 plant physiological forcing in determining future global water stress

Future levels of water stress depend on changes in several key factors including population, climate-change driven water availability, and a carbon dioxide physiological-forcing effect on evaporation and run-off. In this study we use an ensemble of the HadCM3 climate model forced with a range of future emissions scenarios combined with a simple water scarcity index to assess the contribution of each of these factors to the projected population living in water stress over the 21st century.Population change only scenarios increase the number of people living in water stress such that at peak global population 65% of people experience some level of water stress. Globally, the climate model ensemble projects an increase in water availability which partially offsets some of the impacts of population growth. The result is 1 billion fewer people living in water stress by the 2080s under the high end emissions scenarios than if population increased in the absence of climate change.This study highlights the important role plant-physiological forcing has on future water resources. The effect of rising CO₂ is to increase available water and to reduce the number of people living in high water stress by around 200 million compared to climate only projections. This effect is of a similar order of magnitude to climate change.     

碳中和行动的国际趋势分析

中国在第75届联合国大会一般性辩论上提出2060碳中和目标.考虑到已有研究较少关注碳中和或缺少对其国际形势的认识,文中梳理分析了全球31个碳中和承诺国的目标内容和政策法规文件.通过对国际碳中和行动的趋势分析和评述,认为碳中和正在成为全球气候行动关注的重要内容,对于推进全球应对气候变化具有积极意义;而欧盟等发达国家/地区...     

Impact of climate and socioeconomic changes on fire carbon emissions in the future: Sustainable economic development might decrease future emissions

Fires and their associated carbon and air pollutant emissions have a broad range of environmental and societal impacts, including negative effects on human health, damage to terrestrial ecosystems, and indirect effects that promote climate change. Previous studies investigated future carbon emissions from the perspective of response to climate change and population growth, but the compound effects of other factors like economic development and land use change are not yet well known. We explored fire carbon emissions throughout the 21st century by changing five factors (meteorology, biomass, land use, population density, and gross domestic product [GDP] per capita). Compared to the historical period (2006–2015), global future fire carbon emissions decreased, mainly caused by an increase in GDP per capita, which leads to improvement in fire management and capitalized agriculture. We found that the meteorological factor has a strong individual effect under higher warming cases. Fires in boreal forests were particularly expected to increase because of an increase in fuel dryness. Our research should help climate change researchers consider fire-carbon interactions. Incorporating future spatial changes under diverse scenarios will be helpful to develop national mitigation and adaptation plans.     

Ranking the risk of CO2 emissions from seagrass soil carbon stocks under global change threats

Seagrass meadows are natural carbon storage hotspots at risk from global change threats, and their loss can result in the remineralization of soil carbon stocks and CO₂ emissions fueling climate change. Here we used expert elicitation and empirical evidence to assess the risk of CO₂ emissions from seagrass soils caused by multiple human-induced, biological and climate change threats. Judgments from 41 experts were synthesized into a seagrass CO₂ emission risk score based on vulnerability factors (i.e., spatial scale, frequency, magnitude, resistance and recovery) to seagrass soil organic carbon stocks. Experts perceived that climate change threats (e.g., gradual ocean warming and increased storminess) have the highest risk for CO₂ emissions at global spatial scales, while direct threats (i.e., dredging and building of a marina or jetty) have the largest CO₂ emission risks at local spatial scales. A review of existing peer-reviewed literature showed a scarcity of studies assessing CO₂ emissions following seagrass disturbance, but the limited empirical evidence partly confirmed the opinion of experts. The literature review indicated that direct and long-term disturbances have the greatest negative impact on soil carbon stocks per unit area, highlighting that immediate management actions after disturbances to recover the seagrass canopy can significantly reduce soil CO₂ emissions. We conclude that further empirical evidence assessing global change threats on the seagrass carbon sink capacity is required to aid broader uptake of seagrass into blue carbon policy frameworks. The preliminary findings from this study can be used to estimate the potential risk of CO₂ emissions from seagrass habitats under threat and guide nature-based solutions for climate change mitigation.     

How the future of the global forest sink depends on timber demand,forest management,and carbon policies

Deforestation has contributed significantly to net greenhouse gas emissions, but slowing deforestation, regrowing forests and other ecosystem processes have made forests a net sink. Deforestation will still influence future carbon fluxes, but the role of forest growth through aging, management, and other silvicultural inputs on future carbon fluxes are critically important but not always recognized by bookkeeping and integrated assessment models. When projecting the future, it is vital to capture how management processes affect carbon storage in ecosystems and wood products. This study uses multiple global forest sector models to project forest carbon impacts across 81 shared socioeconomic (SSP) and climate mitigation pathway scenarios. We illustrate the importance of modeling management decisions in existing forests in response to changing demands for land resources, wood products and carbon. Although the models vary in key attributes, there is general agreement across a majority of scenarios that the global forest sector could remain a carbon sink in the future, sequestering 1.2–5.8 GtCO2e/yr over the next century. Carbon fluxes in the baseline scenarios that exclude climate mitigation policy ranged from −0.8 to 4.9 GtCO2e/yr, highlighting the strong influence of SSPs on forest sector model estimates. Improved forest management can jointly increase carbon stocks and harvests without expanding forest area, suggesting that carbon fluxes from managed forests systems deserve more careful consideration by the climate policy community.     

IPCC《气候变化与土地特别报告》对陆气相互作用的新认知

IPCC向全球正式发布了其最新的《气候变化与土地特别报告》（SRCCL）,从陆气相互作用、荒漠化、土地退化、粮食安全、综合变化和协同性、可持续土地管理等方面评估气候变化与土地的相互关联。报告是在IPCC 3个工作组共同主导下,首次系统评估气候变化与陆面过程和土地利用/土地管理之间的相关作用。报告的评估结果表明,全球陆地增温幅度接近全球海陆平均值的两倍,气候变化加重了综合土地压力,并严重影响全球粮食安全,而全球很多区域的极端天气气候事件频率/强度持续增加,加重了农业生产的灾害风险和损失。采取行业间和国家间协同一致的行动,通过可持续土地管理,可以有效地适应和减缓气候变化,同时减轻土地退化、荒漠化和粮食安全的压力。     

Changed thinning regimes may increase carbon stock under climate change: A case study from a Finnish boreal forest

A physiological growth and yield model was applied for assessing the effects of forest management and climate change on the carbon (C) stocks in a forest management unit located in Finland. The aim was to outline an appropriate management strategy with regard to C stock in the ecosystem (C in trees and C in soil) and C in harvested timber. Simulations covered 100 years using three climate scenarios (current climate, ECHAM4 and HadCM2), five thinning regimes (based on current forest management recommendations for Finland) and one unthinned. Simulations were undertaken with ground true stand inventory data (1451 hectares) representing Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula) stands. Regardless of the climate scenario, it was found that shifting from current practices to thinning regimes that allowed higher stocking of trees resulted in an increase of up to 11% in C in the forest ecosystem. It also increased the C in the timber yield by up to 14%. Compared to current climatic conditions, the mean increase over the thinning regimes in the total C stock in the forest ecosystem due to the climate change was a maximum of 1%; but the mean increase in total C in timber yield over thinning regimes was a maximum of 12%.     

碳市场与电力市场机制影响下发电机组成本分析与竞争力研究

碳市场和电力市场将共同发挥市场对资源优化配置的决定性作用,对共同市场主体发电企业带来经营和发展挑战.在考虑碳成本的基础上,采用发电机组经济性影响模型,定量分析了碳市场不同发展阶段对发电机组发电成本的影响,定量评价不同能源结构投资收益经济性,以及对集中竞价市场出清顺序的影响.结果表明,随着有偿配额比例和碳价增加,碳成本占...     

Magnitude,distribution and causes of terrestrial carbon sinks and some implications for policy

Abstract

Recent analyses continue to modify our understanding of terrestrial carbon sinks. The sinks are large and variable enough to account for much of the variability in the growth rate of atmospheric CO₂. They are distributed throughout both northern mid-latitudes and the tropics. Identification of the factors influencing an observed sink is extremely difficult; methods for attribution are reviewed. Although various ecological mechanisms (e.g. CO₂ fertilization, nitrogen deposition, climatic variability) have been shown experimentally to have short-term effects on physiological processes controlling the amount of carbon in terrestrial ecosystems, it is unclear which of these mechanisms has been most important in the past 10–100 years and which will be most important in the future. The decades-long supposition that CO₂ fertilization has been a major driver of terrestrial carbon uptake is being challenged. A major portion of the sink in the northern mid-latitudes (although probably not in the tropics) is a result of recovery from past changes in land use and management. To the extent that these direct human actions explain most of the current (and future) sink, attribution and thus accounting become more tractable, but the continued functioning of the sink is limited and largely dependent on deliberate actions (e.g. afforestation, sustainable forest management and preservation).     

Land-use and sustainability under intersecting global change and domestic policy scenarios: Trajectories for Australia to 2050

Understanding potential future influence of environmental, economic, and social drivers on land-use and sustainability is critical for guiding strategic decisions that can help nations adapt to change, anticipate opportunities, and cope with surprises. Using the Land-Use Trade-Offs (LUTO) model, we undertook a comprehensive, detailed, integrated, and quantitative scenario analysis of land-use and sustainability for Australia’s agricultural land from 2013–2050, under interacting global change and domestic policies, and considering key uncertainties. We assessed land use competition between multiple land-uses and assessed the sustainability of economic returns and ecosystem services at high spatial (1.1 km grid cells) and temporal (annual) resolution. We found substantial potential for land-use transition from agriculture to carbon plantings, environmental plantings, and biofuels cropping under certain scenarios, with impacts on the sustainability of economic returns and ecosystem services including food/fibre production, emissions abatement, water resource use, biodiversity services, and energy production. However, the type, magnitude, timing, and location of land-use responses and their impacts were highly dependent on scenario parameter assumptions including global outlook and emissions abatement effort, domestic land-use policy settings, land-use change adoption behaviour, productivity growth, and capacity constraints. With strong global abatement incentives complemented by biodiversity-focussed domestic land-use policy, land-use responses can substantially increase and diversify economic returns to land and produce a much wider range of ecosystem services such as emissions abatement, biodiversity, and energy, without major impacts on agricultural production. However, better governance is needed for managing potentially significant water resource impacts. The results have wide-ranging implications for land-use and sustainability policy and governance at global and domestic scales and can inform strategic thinking and decision-making about land-use and sustainability in Australia. A comprehensive and freely available 26 GB data pack (http://doi.org/10.4225/08/5604A2E8A00CC) provides a unique resource for further research. As similarly nuanced transformational change is also possible elsewhere, our template for comprehensive, integrated, quantitative, and high resolution scenario analysis can support other nations in strategic thinking and decision-making to prepare for an uncertain future.     

An International Relations perspective on the global politics of carbon dioxide capture and storage

With the publication of the IPCC Special Report on Carbon dioxide Capture and Storage (CCS), CCS has emerged as a focal issue in international climate diplomacy and energy collaboration. This paper has two goals. The first goal is to map CCS activities in and among various types of intergovernmental organisations; the second goal is to apply International Relations (IR) theories to explain the growing diversity, overlap and fragmentation of international organisations dealing with CCS. Which international organisations embrace CCS, and which refrain from discussing it at all? What role do these institutions play in bringing CCS forward? Why is international collaboration on CCS so fragmented and weak? We utilise realism, liberal institutionalism and constructivism to provide three different interpretations of the complex global landscape of CCS governance in the context of the similarly complicated architecture of global climate policy. A realist account of CCS's fragmented international politics is power driven. International fossil fuel and energy organisations, dominated by major emitter states, take an active role in CCS. An interest-based approach, such as liberal institutionalism, claims that CCS is part of a “regime complex” rather than an integrated, hierarchical, comprehensive and international regime. Such a regime complex is exemplified by the plethora of international organisations with a role in CCS. Finally, constructivism moves beyond material and interest-based interpretations of the evolution of the institutionally fragmented architecture of global CCS governance. The 2005 IPCC Special Report on CCS demonstrates the pivotal role that ideas, norms and scientific knowledge have played in transforming the preferences of the international climate-change policy community.