Nouvelles

This week the global press is flush with news and views on the IPCC’s Fifth Assessment Report on impacts of climate change. Highly recommended reading is the report’s authoritative, wide-reaching appraisal of food and farming in Chapter 7, which the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) has condensed into a brief analysis paper released today. Impressive advances in science have been made since the last report in 2007. A keystone among the new findings on agriculture is a synthesis of no fewer than 1700 published simulations of future crop yields under climate change.

The synthesis, also published independently as A meta-analysis of crop yield under climate change and adaptation, by Andy Challinor, James Watson, David Lobell, Mark Howden, Daniel Smith and Netra Chhetri, distills the consensus among modellers on future yields of the major food security crops – rice, wheat and maize – that deliver 48% of the calories we consume. The big take-home message is that climate change depresses yields. Even moderate climate change, anticipated in the next few decades, is associated with yield losses. By the second half of the century two-thirds of simulations project yield decreases of more than 10%.

But is this really a big deal? After all, maize yields in the USA increased 600% over the 20^th century. Looking forward, scientists argue that yield increases of 45-70% are possible for most crops through improved nutrient management and increased use of irrigation. Climate change may exert a drag on yield growth, but perhaps technology and careful use of resources can more than compensate.

The trouble with such techno-optimism is twofold. First, as Challinor and co-authors carefully present in their meta-analysis, much is unknown. Most models do not consider future trends in water availability, pests and diseases, or climatic extremes such as floods and heatwaves. Second, the broad-brush global findings hide significant regional variations. Of most concern is the greater hit to tropical agriculture. The minority of simulations that project yield gains in the 2080s are all from temperate regions. Worryingly, the models also throw some doubt on the value of adaptation in the tropics. Simulations for the 2040s and 2050s that include on-farm adaptations – changes in planting date, fertilizer, irrigation, cultivar or other agronomic practices – give a yield benefit of 14% for temperate crops, but no discernible benefit for tropical crops.

Social realities compound the outlook of the models. Poverty and food insecurity will continue to be concentrated in tropical rural areas for some decades to come. People here, even if they have access to globally marketed food from temperate regions, depend heavily on farming, fisheries and livestock for the incomes they need to purchase that food. With limited assets they are less able to weather droughts and disasters, or to adopt emerging adaptation options. Food security under climate change may call for bigger changes than we have imagined – maybe even shifting our diets away from cereals to more heat-tolerant crops.  Major transitions necessitate support from all of us in the global community, support that we must surely steer towards poor food producers in tropical countries.

Links

• Porter JR, Xie L, Challinor A, Cochrane K, Howden M, Iqbal MM, Lobell D, Travasso MI. 2014. Food Security and Food Production Systems. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. 
• Vermeulen SJ. 2014. Climate change, food security and small-scale producers. CCAFS Info Brief. CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). Copenhagen, Denmark. 
• Challinor AJ, Watson J, Lobell DB, Howden SM, Smith DR, Chhetri N. 2014. A meta-analysis of crop yield under climate change and adaptation. Nature Climate Change. doi: 10.1038/NCLIMATE2153
• FAOSTAT data for 2009. http://faostat3.fao.org/faostat-gateway/go/to/download/FB/FB/E
• Edgerton MD. 2009. Increasing crop productivity to meet global needs for feed, food, and fuel. Plant Physiology 149: 7-13. DOI: http://dx.doi.org/10.1104/pp.108.130195
• Mueller ND, Gerber JS, Johnston M, Ray DK, Ramankutty N, Foley JA. 2012. Closing yield gaps through nutrient and water management. Nature 490: 254–257. http://dx.doi.org/10.1038/nature11420

Infographic data sources:

• ECLAC (2009). (LC/G.2425): The Economics of Climate Change in Central America: Summary 2010. United Nations, Santiago de Chile, Chile.
• Lobell DB, Burke MB, Tebaldi C, Mastrandrea MD, Falcon WP, Naylor RL. 2008. Prioritizing Climate Change Adaptation Needs for Food Security in 2030. Science 319(5863): 607-610.
• Thornton PK, Jones PG, Alagarswamy G, Andresen J, Herrero M. 2010. Adapting to climate change: Agricultural system and household impacts in East Africa. Agricultural Systems 103(2): 73-82.
• Wratt D, Mullan B, Tait A, Woods R, Baisden T, Giltrap D, Lock K, Hendy J, Kerr S, Stroombergen A, Stojanovik A. 2008. Costs and benefits of climate change and adaptation to climate change in New Zealand agriculture: what do we know so far? Contract report by EcoClimate Consortium: Integrated Research on the Economics of Climate Change Impacts Adaptation and Mitigation, Wellington, Ministry of Agriculture and Forestry.