Avoiding dangerous climate change: analysis with an integrated assessment model

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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.