Meta-analysis of crop simulations highlights need for adaptation measures

Crop-level adaptation measures such as changes in varieties, planting date and irrigation can offset some of these declines

By Paul NeateClimate change is changing the face of agriculture – rising temperatures, changing rainfall patterns and the evolution of pests and diseases all pose threats to food production. Modelling has been used extensively to predict the likely impacts of climate change on crop yields and ranges, but different studies give different answers, often as a consequence of the variety of scenarios tested and analytical approaches used.

Meta-analyses – analysing results from numerous studies – can help bring order to this diversity, identifying patterns and areas of consensus. One such study conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change in 2007 concluded that up to 2 °C of warming could result in increased yields of wheat, rice and maize, but that higher temperatures would likely result in yield declines. It also demonstrated that simulated crop-level adaptations – such as changes to varieties grown and to agronomic practices – significantly increased yields of all crops, in all regions and at all levels of warming.

But there have been many more projections of the impact of climate change on crop production since 2007. This latest meta-analysis, which informed the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), used an update of the 2007 data set with over twice as many studies, and set out to answer three related questions: What are the likely impacts of differing degrees of climate change on yields, by crop and by region? How far can adaptation measures offset the impacts of changes in temperature and rainfall? Will yields increase or decrease in the remaining decades of this century, and by how much?

Overall, the results of the new meta-analysis indicate a greater risk that climate change will reduce yields of wheat, rice and maize in both temperate and tropical regions unless adaptation measures are taken. This contrasts with the findings of the earlier study, which suggested that moderate temperature changes would result in increased yields in temperate regions.

There would be a clear benefit for wheat and rice in adopting adaptation measures, such as irrigation, fertilisers, or changes in cultivated varieties. The benefits would be less apparent for maize. Overall, crop-level adaptation measures could help to avoid yield declines in wheat, and could even increase yields by 7–15% in some situations, relative to yields of non-adapted crops. The authors note that these adaptation benefits could increase or decrease due to social or economic barriers including low capacity to implement different farming approaches, or cultural and political factors that make a certain technology inappropriate.

More than 70% of the projections indicate that crop yields will be lower in the 2040s and 2050s than they are now, with nearly half of projections indicating declines of more than 10% in the second half of the century. Moreover, over a quarter of all projections indicate yield declines of 25% or more after 2050. These projections include simulations of adapted crops, which suggest that farm-level adaptation could offset some yield declines resulting from climate change in the first half of the century but that more radical adaptation measures – different crops or completely different production systems – may be needed in the latter part of the century.

These averages mask important differences. For example, models indicate yield increases in the 2070s and 2090s, but only for temperate crops – yields of tropical crops in all cases decline. In addition, only a handful of studies provided indications of year-to-year variation of yields rather than just time-averaged yields. These studies indicate that yield variability is likely to increase as climate change progresses. If more climate-impact studies reported yield variability, instead of using it only to obtain average changes, meta-analyses would be better able to assess the challenges for adaptation posed by increases in variability and extreme events. The food price spikes observed after major extreme events caused crop failure such as in Russia in 2010 and Australia in 2007 – illustrate the importance of this topic.

A related paper, Making the most of climate impact ensembles, also published in Nature Climate Change, demonstrates the benefits of increasing coordination among modelling groups, and of developing links between climate models and impact models.

Approaches that combine global impacts modelling expertise with food security research show great promise. Recent examples from the CGIAR Research Program on Climate Change, Agriculture and Food Security (a Future Earth strategic partner), include a study by Claessens et al. (2012), which combined field surveys and modelling with projected socio-economic pathways to analyse the socio-economics of agricultural systems in Kenya. A field study on trends in farming practices East Africa showed that adaptation is occurring and that improves food security at the household level (Kristjanson et al. 2012). This study combined modelling with social research techniques. The more that global impacts modelling communities can work with agriculture and food security researchers, the more likely they are to deliver results that allow the world’s farmers to adapt to climate change.

This article was written by Paul Neate on behalf of the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). 

Related reading:

Challinor et al. A meta-analysis of crop yield under climate change and adaptation, Nature Climate Change 4, 287–291 (2014) http://dx.doi.org/10.1038/nclimate2153

Claessens et al. A method for evaluating climate change adaptation strategies for small-scale farmers using survey, experimental and modeled data, Agricultural Systems 111, 85–95 (2012) http://dx.doi.org/10.1016/j.agsy.2012.05.003

Kristjanson et al. Are food insecure smallholder households making changes in their farming practices? Evidence from East Africa, Food Security 4(3), 318 – 397 (2012) http://dx.doi.org/10.1007/s12571-012-0194-z

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.