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（称为减缓）。《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“防止气候系统受到危险的人为干扰……在一个足够的时间框架内，使生态系统能够自然地适应气候变化，确保粮食生产不受威胁，并使经济发展能够以可持续的方式进行。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，从而了解排放途径的潜在目标，决策者需要评估与这些备选未来情景相关的风险和成本。这方面的资料还应附有广泛的不确定性分析，但迄今为止大部分还没有提供这种分析。这些情景的风险和成本可以通过计算机综合评估（IA）模型进行研究，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（如水资源压力、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（如生物多样性、植被群落的变化）及其相关服务的影响的组成代码联系在一起。该提案以使用我与同事建立的社区IA系统（CIAS）的这些类型的分析为中心。我的研究的第一个目标是，与基线“无政策”情景相比，使用CIAS对在更严格的稳定（同时减缓）情景下可能避免的损害以及可能存在的适应挑战进行风险评估。为了确定通往某一稳定情景的途径，政策制定者将需要关于备选缓解政策的经济成本和技术可行性的信息。为了提供这些补充信息，我将借鉴我在剑桥大学的合作者Terry Barker的工作。不确定性分析是正确执行风险评估的关键。因此，我将通过与哈德利中心和气候预测网项目的合作，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)未来可选的社会经济情景；(e)使用不同机构编写的不同模块代码。我将探讨关于稳定的特定途径的动态问题，以及暂时超过所考虑的最终稳定水平可能会如何影响影响。我将启动气候对经济影响反馈的新研究，同时考虑渐进气候变化和极端天气事件的影响，在综合评估模型方面开辟新的领域。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；（ii）避免森林砍伐（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潜力。这项研究将为获得诺贝尔和平奖的政府间气候变化专门委员会今后的评估提供有用的信息。它将伴随着与DEFRA的双向互动，以最大限度地提高项目计划和产出的政策相关性。UKCIP08用户组的成员也将被咨询。信息还将通过期刊论文、《联合国气候变化框架公约》会外活动和两个利益攸关方讲习班传播。

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.