Avoiding dangerous climate change: analysis with an integrated assessment model

未来几年气候政策中最重要的问题之一将是选择适当的减排目标(称为缓解)。《联合国气候变化框架公约》第二条要求将温室气体浓度稳定在以下水平：“防止对气候系统造成危险的人为干扰……在足以使生态系统自然适应气候变化、确保粮食生产不受威胁、并允许经济发展以可持续方式进行的时间框架内”。因此，关键问题是稳定的适当水平和时间尺度。为了最好地了解稳定情景的选择以及排放路径的潜在目标，政策制定者需要评估与这些未来备选情景相关的风险和成本。这一信息还应伴随着广泛的不确定性分析，而这一分析在很大程度上迄今尚未提供。可以使用计算机综合评估(IA)模型来研究这些情景的风险和成本，这些模型将模拟全球经济、地球气候系统和气候变化对人类系统的影响(例如，水压力、农业产量损失、沿海洪水、人类健康风险)以及对自然生态系统(例如，生物多样性、植被群落的变化)及其伴随服务的组件代码连接在一起。该提案以这些类型的分析为中心，使用的是我与同事共同构建的社区IA系统(CIAS)。我研究的第一个目标是使用CIAS对避免的可能损害以及因此可能剩余的适应挑战进行风险评估，在相继更严格的稳定(同时缓解)情景下，与基线的“无政策”情景相比。为了确定通向给定稳定情景的途径，政策制定者需要关于替代缓解政策的经济成本和技术可行性的信息。为了提供这一补充信息，我将借鉴我在剑桥大学的合作者特里·巴克的工作。不确定性分析是正确进行风险评估的关键。因此，我将通过与哈德利中心和气候预测网项目合作，评估以下方面产生的不确定性：(A)关键气候模型参数；(B)全球大气环流模型产生的空间气候预测模式的多样性；(C)经济和影响模块内的参数；(D)替代的未来社会经济情景；(E)不同机构编写的不同模块代码的使用。我将探讨与实现稳定的具体途径有关的动态问题，以及所考虑的最终稳定水平暂时超标可能如何影响影响。我将启动关于气候影响对经济的反馈的新研究，同时考虑到逐渐气候变化的影响和极端天气事件的影响，在综合评估模型方面开辟新的天地。第三个目标是研究土地利用变化的影响及其与当今人类应对气候变化的两个关键因素的关系：(I)大规模种植生物燃料的影响和(Ii)避免砍伐森林(目前占全球排放量的近25%)在气候缓解政策中发挥重要作用的可能性。这项研究将为诺贝尔和平奖获得者政府间气候变化专门委员会未来的评估提供有用的信息。它将与DEFRA进行双向互动，以最大限度地提高项目计划和产出的政策相关性。还将征求UKCIP08用户组成员的意见。还将通过期刊论文、《气候公约》会外活动和2个利益攸关方讲习班传播信息。

One of the most important issues in climate policy over the next few years will be the choice of appropriate targets for emission reductions (known as mitigation). Article 2 of the United Nations Framework Convention on Climate Change requires stabilization of greenhouse gas concentrations at a level that would 'prevent dangerous anthropogenic interference with the climate system ... within a timeframe sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to allow economic development to proceed in a sustainable manner'. The key question therefore is the appropriate level and timescale for the stabilization. In order to best inform the choice of stabilization scenario and hence the potential targets for emission pathways, policy makers need assessments of the risks and costs associated with these alternative future scenarios. This information should also be accompanied by an extensive uncertainty analysis, which has, for the most part, not been provided to date. The risks and costs of these scenarios can be studied with computer integrated assessment (IA) models that link together component codes simulating the global economy, earth's climate system, and impacts of climate change upon human systems (e.g., water stress, agricultural yield losses, coastal flooding, human health risks , and on natural ecosystems (e.g., biodiversity, shifts in vegetation communities) and their accompanying services. The proposal centres on these types of analyses using the Community IA System (CIAS) that I have built with colleagues. The first objective of my research is to use CIAS to provide a risk assessment of the likely damages avoided, and hence the likely adaptation challenges remaining, under successively more stringent stabilization (and concurrently mitigation) scenarios, compared to a baseline 'no policy' scenario. In order to determine the pathway to a given stabilization scenario, policy makers will need information about the economic costs and technological feasibility of alternative mitigation policies. To provide this complementary information I will draw on the work of my collaborator Terry Barker at the University of Cambridge. Uncertainty analysis is key to properly performing a a risk assessment. Therefore I will assess uncertainties arising from (a) key climate model parameters through collaboration with the Hadley Centre and the Climate Prediction.net project (b) the diversity of spatial climate projection patterns arising from Global General Circulation Models (c) parameters within economic and impacts modules (d) alternative future socioeconomic scenarios and (e) use of different module codes written at different institutions. I will explore dynamic issues concerning the particular pathway towards stabilization and how impacts might be affected by temporarily overshooting of the ultimate stabilization levels being considered. I will initiate new studies of the feedbacks of climate impacts on the economy, considering both the effects of gradual climate change those of extreme weather events, breaking new ground in integrated assessment modelling. The third aim is to study the implications of land use change and its relationship with two critical elements of the human response to climate change today: (i) implications of large scale cropping of biofuels and (ii) the potential for avoided deforestation (now making up nearly 25% of global emissions) to play a major role in climate mitigation policy. The research will contribute useful information towards future assessments by the Nobel Peace Prize winning Intergovernmental Panel on Climate Change. It will be accompanied by a 2-way interaction with DEFRA to maximise policy relevance of project plans and outputs. Members of the UKCIP08 User Group will also be consulted. Information will be disseminated also via journal papers, UNFCCC side-events, and 2 stakeholder workshops.