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Potential interactions between food production and climate mitigation are explored for two situations in sub-Saharan Africa, where deforestation and land degradation overlap with hunger and poverty. Three agriculture intensification scenarios for supplying nitrogen to increase crop production (mineral fertilizer, herbaceous legume cover crops--green manures--and agroforestry--legume improved tree fallows) are compared to baseline food production, land requirements to meet basic caloric requirements, and greenhouse gas emissions. At low population densities and high land availability, food security and climate mitigation goals are met with all intensification scenarios, resulting in surplus crop area for reforestation. In contrast, for high population density and small farm sizes, attaining food security and reducing greenhouse gas emissions require mineral fertilizers to make land available for reforestation; green manure or improved tree fallows do not provide sufficient increases in yields to permit reforestation. Tree fallows sequester significant carbon on cropland, but green manures result in net carbon dioxide equivalent emissions because of nitrogen additions. Although these results are encouraging, agricultural intensification in sub-Saharan Africa with mineral fertilizers, green manures, or improved tree fallows will remain low without policies that address access, costs, and lack of incentives. Carbon financing for small-holder agriculture could increase the likelihood of success of Reducing Emissions from Deforestation and Forest Degradation in Developing Countries programs and climate change mitigation but also promote food security in the region. carbon sequestration | land-use/cover change | nitrous oxide emissions doi/ 10.1073/pnas.0912248107

Byline: Valentina Bosetti (1,2), Carlo Carraro (1,2,3,4,5), Alessandra Sgobbi (1,2), Massimo Tavoni (1,2,6) Abstract: Despite the growing concern about actual on-going climate change, there is little consensus on the scale and timing of actions needed to stabilise the concentrations of greenhouse gases. Many countries are unwilling to implement mitigation strategies, at least in the short term, and no agreement on an ambitious global stabilisation target has yet been reached. It is thus likely that international climate policies will be characterized by a high degree of uncertainty over the stringency of the climate objective, and that some countries might delay their participation to global action. What additional economic costs will this delay in the adoption of mitigation measures imply? What would the optimal short-term strategy be given the uncertainty surrounding the climate policy to come? Is there a hedging strategy that decision makers can adopt to cope with delayed action and uncertain targets? This paper addresses these questions by quantifying the economic implications of delaying mitigation action, and by computing the optimal abatement strategy in the presence of uncertainty about a global stabilisation target (which will be agreed upon in future climate negotiations). Results point to short-term inaction as the key determinant for the economic costs of ambitious climate policies. They also indicate that there is an effective hedging strategy that could minimise the cost of climate policy uncertainty over the global stabilisation target: a short-term moderate climate policy would be a good strategy to reduce the costs of delayed action and to cope with uncertainty about the outcome of future climate negotiations. By contrast, failing to curb emissions in the short term imposes rapidly increasing additional costs of compliance. Author Affiliation: (1) Fondazione Eni Enrico Mattei, Corso Magenta 63, Milan, Italy (2) CMCC, Lecce, Italy (3) University of Venice, Venice, Italy (4) CEPR, London, UK (5) CESifo, Munich, Germany (6) Catholic University of Milan, Milan, Italy Article History: Registration Date: 09/06/2009 Received Date: 02/06/2008 Accepted Date: 06/03/2009 Online Date: 23/07/2009 Article note: This paper is part of the research work being carried out by the Climate Change Modelling and Policy Research Programme of the Fondazione Eni Enrico Mattei and by the Climate Impacts and Policy Division of the EuroMediterranean Center on Climate Change. Financial support from the Italian Ministry of the Environment is acknowledged. The financial support of the EC 6FP TranSust.Scan project--Scanning Policy Scenarios for the Transition to Sustainable Economic Structures--is gratefully acknowledged. The authors are grateful for useful comments from participants to the Conference on the 'Economics of Climate Change and Sustainable Development', Chia, Italy, September 2007. The usual disclaimer applies.

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