Despite substantial advances in climate change impact research in recent years, the scientific basis for damage functions in economic models used to calculate the social cost of carbon (SCC) is either undocumented, difficult to trace, or based on a small number of dated studies. Here we present new damage functions based on the current scientific literature and introduce these into an integrated assessment model (IAM) in order to estimate a new SCC. We focus on the agricultural sector, use two methods for determining the yield impacts of warming, and the GTAP CGE model to calculate the economic consequences of yield shocks. These new damage functions reveal far more adverse agricultural impacts than currently represented in IAMs. Impacts in the agriculture increase from net benefits of $2.7 ton−1 CO2 to net costs of $8.5 ton−1, leading the total SCC to more than double.

Global change drivers of land-use/cover change (LUCC) like population dynamics, economic development, and climate change are increasingly important to local sustainability studies, and can only be properly analyzed at fine-scales that capture local biophysical and socio-economic conditions. When sufficiently widespread, local feedback to stresses originating from global drivers can have regional, national, and even global impacts. A multiscale, global-to-local-to-global (GLG) framework is thus needed for comprehensive analyses of LUCC and leakage. The number of GLG-LUCC studies has grown substantially over the past years, but no reviews of this literature and their contributions have been completed so far. In fact, the largest body of literature pertains to global-to-local impacts exclusively, whereas research on local feedback to regional, national, and global spheres remain scarce, and are almost solely undertaken within large modeling institutes. As such, those are rarely readily accessible for modification and extension by outside contributors. This review of the recent GLG-LUCC studies calls for more open-source modeling and availability of data, arguing that the latter is the real constraint to more widespread analyses of GLG-LUCC impacts. Progress in this field will require contributions from hundreds of researchers around the world and from a wide variety of disciplines.

Organisation de Coopération et de Développement Économiques Organisation for Economic Co-operation and Development 08-Aug-2016 ___________________________________________________________________________________________ _____________ English -Or. English ENVIRONMENT DIRECTORATE IMPLICATIONS OF WATER SCARCITY FOR ECONOMIC GROWTH -ENVIRONMENT WORKING PAPER No. 109 by Thomas W. Hertel (1), Jing Liu (1)(1) Purdue University, USA OECD Working Papers should not be reported as representing the official views of the OECD or of its member countries. The opinions expressed and arguments employed are those of the author(s).

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Incorporating water into a computable general equilibrium (CGE) model operating at global scale can be extremely demanding due to the absence of standardized data, the sheer dimensions caused by intersecting river basins with countries, and difficulties to model demand for and supply of water. This has led many authors to introduce water in their CGE modeling framework in different ways and at different spatial and sectoral aggregation levels. Of course, simplifying market for water and sacrificing the geographical realism risk introducing errors caused by inappropriate aggregation. In this paper we use a global CGE model which distinguished between rainfed and irrigated crops and traces supply of and demand for water at river basin by agro ecological zone (AEZ) and country to investigate the three most commonly practiced simplifications: 1) tackling global questions in a national level model; 2) collapsing irrigated and rainfed crop production into a single sector; and 3) removing river basin boundaries within a country. In each case, we compare their performance in predicting the impacts of future irrigation scarcity on international trade, crop output, prices and land use change, relative to the full scale model. As might be expected, the single region model does a pretty good job of matching outcomes for that region, although changes in bilateral trade can entail significant errors. When it comes to the elimination of sub-national river basins and irrigation location, we find that, if the research question has to do with changes in national-scale trade, production, consumption, and prices, it may be sufficient to ignore the sub-national water and land heterogeneity in global economic analysis of water scarcity. However, when decision makers have an interest in the distribution of inputs and outputs within a region, preserving the river basin and sectoral detail in the model brings considerable added value to the analysis.