Symposium on Social Theory and the Environment in the New World (dis)OrderInternational audienceIn West Africa, agriculture, mainly rainfed, is a major economic sector and the one most vulnerable to climate change. A meta-database of future crop yields, built up from 16 recent studies, is used to provide an overall assessment of the potential impact of climate change on yields, and to analyze sources of uncertainty. Despite a large dispersion of yield changes ranging from -50% to +90%, the median is a yield loss near -11%. This negative impact is assessed by both empirical and process-based crop models whereas the Ricardian approach gives very contrasted results, even within a single study. The predicted impact is larger in northern West Africa (Sudano-Sahelian countries, -18% median response) than in southern West Africa (Guinean countries, -13%) which is likely due to drier and warmer projections in the northern part of West Africa. Moreover, negative impacts on crop productivity increase in severity as warming intensifies, with a median yield loss near -15% with most intense warming, highlighting the importance of global warming mitigation. The consistently negative impact of climate change results mainly from the temperature whose increase projected by climate models is much larger relative to precipitation change. However, rainfall changes, still uncertain in climate projections, have the potential to exacerbate or mitigate this impact depending on whether rainfall decreases or increases. Finally, results highlight the pivotal role that the carbon fertilization effect may have on the sign and amplitude of change in crop yields. This effect is particularly strong for a high carbon dioxide concentration scenario and for C3 crops (e.g. soybean, cassava). As staple crops are mainly C4 (e.g. maize, millet, sorghum) in WA, this positive effect is less significant for the region. (C) 2011 Elsevier Ltd. All rights reserved

Sub-Saharan West Africa is a vulnerable region where a better quantification and understanding of the impact of climate change on crop yields is urgently needed. Here, we have applied the process-based crop model SARRA-H calibrated and validated over multi-year field trials and surveys at eight contrasting sites in terms of climate and agricultural practices in Senegal, Mali, Burkina Faso and Niger. The model gives a reasonable correlation with observed yields of sorghum and millet under a range of cultivars and traditional crop management practices. We applied the model to more than 7000 simulations of yields of sorghum and millet for 35 stations across West Africa and under very different future climate conditions. We took into account 35 possible climate scenarios by combining precipitation anomalies from −20% to 20% and temperature anomalies from +0 to +6 • C.We found that most of the 35 scenarios (31/35) showed a negative impact on yields, up to −41% for +6 • C/ − 20% rainfall. Moreover, the potential future climate impacts on yields are very different from those recorded in the recent past. This is because of the increasingly adverse role of higher temperatures in reducing crop yields, irrespective of rainfall changes. When warming exceeds +2 • C, negative impacts caused by temperature rise cannot be counteracted by any rainfall change. The probability of a yield reduction appears to be greater in the Sudanian region (southern Senegal, Mali, Burkina Faso, northern Togo and Benin), because of an exacerbated sensitivity to temperature changes compared to the Sahelian region (Niger, Mali, northern parts of Senegal and Burkina Faso), where crop yields are more sensitive to rainfall change. Finally, our simulations show that the photoperiod-sensitive traditional cultivars of millet and sorghum used by local farmers for centuries seem more resilient to future climate conditions than modern cultivars bred for their high yield potential (−28% versus −40% for the +4 • C/ − 20% scenario). Photoperiod-sensitive cultivars counteract the effect of temperature increase on shortening cultivar duration and thus would likely avoid the need to shift to cultivars with a greater thermal time requirement. However, given the large difference in mean yields of the modern versus traditional varieties, the modern varieties would still yield more under optimal fertility conditions in a warmer world, even if they are more affected by climate change.

Border adjustments are currently discussed to limit the possible adverse impact of climate policies on competitiveness and carbon leakage. We discuss the main choices that will have to be made if the European Union implements such a system alongside with the EU ETS. Although more analysis is required on some issues, on others some design options seem clearly preferable to others. First, the import adjustment should be a requirement to surrender allowances rather than a tax. Second, the general rule to determine the amount of allowances per ton imported should be the product-specific benchmarks that the European Commission is currently elaborating for a different purpose (i.e. to determine the amount of free allowances). Third, this obligation should apply when the exported product is registered at the EU border, and not after the end of the year as is the case for domestic emitters. Fourth, the export adjustment should take the form of a rebate on the amount of allowances a domestic emitter has to surrender. Five, this rebate should equal the abovementioned product-specific benchmarks, not the emissions of the particular exporting plant or firm. Finally, the adjustment does not have to apply to consumer products but mostly to basic products. Keywords AbstractBorder adjustments are currently discussed to limit the possible adverse impact of climate policies on competitiveness and carbon leakage. We discuss the main choices that will have to be made if the European Union implements such a system alongside with the EU ETS. Although more analysis is required on some issues, on others some design options seem clearly preferable to others. First, the import adjustment should be a requirement to surrender allowances rather than a tax. Second, the general rule to determine the amount of allowances per ton imported should be the product-specific benchmarks that the European Commission is currently elaborating for a different purpose (i.e. to determine the amount of free allowances). Third, this obligation should apply when the exported product is registered at the EU border, and not after the end of the year as is the case for domestic emitters. Fourth, the export adjustment should take the form of a rebate on the amount of allowances a domestic emitter has to surrender. Five, this rebate should equal the above-mentioned product-specific benchmarks, not the emissions of the particular exporting plant or firm. Finally, the adjustment does not have to apply to consumer products but mostly to basic products.

The EU ETS has been criticised for threatening the competitiveness of European industry and generating carbon leakage, i.e. increasing foreign greenhouse gas emissions. Two main options have been put forward to tackle these concerns: border adjustments and output-based allocation, i.e. allocation of free allowances in proportion to current production. We compare various configurations of these two options, as well as a scenario with full auctioning and no border adjustment. Against this background, we develop a model of the main sectors covered by the EU ETS: electricity, steel, cement and aluminium. We conclude that the most efficient way to tackle leakage is auctioning with border adjustment, which generally induces a negative leakage (a spillover). Another relatively efficient policy is to combine auctioning in the electricity sector and output-based allocation in exposed industries, especially if free allowances are given both for direct and indirect emissions, i.e. those generated by the generation of the electricity consumed. Although output-based allocation is generally less effective than border adjustment to tackle leakage, it is more effective to mitigate production losses in the sectors affected by the ETS.Keywords : Emission trading, border adjustment, output-based allocation, competitiveness, carbon leakage. Limiter les fuites dans le système européen d'échange de quotas d'émission de gaz à effet deserre : ajustement aux frontières ou allocation basée sur la production courante ? RésuméLe système européen d'échange de quotas d'émission de gaz à effet de serre (GES) a été critiqué comme menaçant la compétitivité de l'industrie européenne et comme générant des fuites de carbone, c'est-à-dire une augmentation des émissions de GES à l'étranger. Principalement, deux options ont été avancées pour traiter ces problèmes : l'ajustement aux frontières et l'allocation basée sur la production, c'est-à-dire une allocation gratuite de permis proportionnelle à la production courante. Nous développons un modèle représentant les principaux secteurs inclus dans le système européen de quotas (électricité, acier, ciment et aluminium) et analysons plusieurs configurations de chacune de ces options, ainsi qu'un scénario avec enchères et sans ajustement aux frontières. Nous trouvons qu'une allocation par l'intermédiaire d'enchères, complétée par un ajustement aux frontières, permet de limiter le plus les fuites de carbone, voire de diminuer les émissions dans les pays hors UE27 (fuites négatives). Une autre politique relativement efficace est de combiner des enchères pour le secteur de l'électricité et une allocation basée sur la production pour les secteurs exposés aux fuites de carbone, en particulier si la quantité de permis distribuée tient compte des émissions directes et indirectes (liées à la génération de l'électricité consommée). Bien que cette dernière option soit généralement moins efficace qu'un ajustement aux frontières pour limiter les fuites de carbone, elle permet néanmoins de réduire les pertes de...

Environmental policies often set "relative" or "intensity" emission caps, i.e., emission limits proportional to the polluting firm's output. One of the arguments put forth in favour of relative caps is based on the uncertainty on business-as-usual output: if the firm's production level is higher than expected, so will be business-as-usual emissions, hence reaching a given level of emissions will be more costly than expected. As a consequence, it is argued, a higher emission level should be allowed if the production level is more important than expected. We assess this argument with a stochastic analytical model featuring two random variables: the business-as-usual emission level, proportional to output, and the slope of the marginal abatement cost curve. We compare the relative cap to an absolute cap and to a price instrument, in terms of welfare impact. It turns out that in most plausible cases, either a price instrument or an absolute cap yields a higher expected welfare than a relative cap.Quantitatively, the difference in expected welfare is typically very small between the absolute and the relative cap but may be significant between the relative cap and the price instrument.

In the Sudano-Sahelian region, which includes South Niger, the inter-annual variability of the rainy season is high and irrigation is scarce. As a consequence, bad rainy seasons have a massive impact on crop yield and regularly entail food crises. Traditional insurances based on crop damage assessment are not available because of asymmetric information and high transaction costs compared to the value of production. We assess the risk mitigation capacity of an alternative form of insurance which has been implemented in India since 2003: insurance based on a weather index. We compare the capacity of various weather indices to increase utility of a representative risk-averse farmer. We show the importance of using plot-level yield data rather than village averages, which bias results upward. We also illustrate the need for out-ofsample estimations in order to avoid overfitting. Even with the appropriate index and assuming a substantial risk aversion, we find a limited gain of implementing insurance, roughly corresponding to the cost of implementing such insurances observed in India. However, when we treat separately the plots with and without fertilizers, we show that the benefit of insurance is higher in the former case. This suggests that insurances may increase the use of risk-increasing inputs like fertilizers and improved cultivars, hence average yields, which are very low in the region.

The European Commission (2001a) has recently presented a directive proposal to the European Parliament and Council in order to implement a greenhouse gas emission trading scheme. If this proposal survives the policy process, it will create the most ambitious trading system ever implemented. However the legislative process is an opportunity for various interest groups to amend environmental policies which, as a result, generally deviate further from what economic literature proposes. A close look at implemented emission trading schemes, stressing their discrepancies with economic literature requests, is thus useful to increase the chances of forthcoming emission trading schemes to go through the political process.We thus review ten emission trading systems, that are either implemented or at an advanced stage of the policy process. We draw attention to major points to be aware of when designing an emission trading system: sectoral and spatial coverage, permits allocation, temporal flexibility, trading organisation, monitoring, enforcement, compliance, and the harmonisation vs. subsidiarity issue. The aim is to evaluate how far experiences in emission trading move away from theory and why.We then provide some lessons and recommendations on how to implement a greenhouse gas emission trading program in Europe. We identify some pros of the Commission proposal (spatial and sectoral coverage, temporal flexibility, trading organisation, compliance rules), some potential drawbacks (allocation rules, monitoring and enforcement) and items on which further guidance is * The authors gratefully acknowledge contributions by two anonymous reviewers and the editors. 3 needed (monitoring and allocation rules). Lastly, the European Commission should devote prominent attention to the U.S. NO X Ozone Transport Commission budget program, as the only example of integration between the federal and state levels.

No abstract