Andy Challinor23.06.2016 | 7:00am
Prof Andy Challinor is professor of climate impacts at the University of Leeds and leads work on climate smart agriculture for the research programme Climate Change, Agriculture and Food Security (CCAFS). He was a lead author on the ‘Food Production Systems and Food Security’ chapter of the Fifth Assessment report of the Intergovernmental Panel on Climate Change, and is a lead author of the forthcoming UK Climate Change Risk Assessment.
Feeding a growing global population as our climate warms will be one of the biggest challenges that we face during this century.
Introducing new crop varieties that thrive in warmer conditions can help farmers make their crops more resilient. But our new study suggests the climate is changing faster than new crops are being developed.
Using maize crops in Africa as a case study, we look at three ways to help crop yields keep pace with rising temperatures, protecting food production in the future.
Maize is Africa’s most widely grown crop. More than 300m Africans depend on it as their main food source.
Yet our recent research suggests that much of sub-Saharan Africa will become increasingly unsuitable for growing maize – and other staple crops – as the climate warms this century. This includes some of the major cereal-producing areas in eastern and southern Africa.
Climate change is expected to reduce maize crop yields in parts of Africa by as much as 40% by 2050, with the largest decreases in western Tanzania, Malawi and the Sahel.
Even with an international effort to cut greenhouse gas emissions, some of these impacts will still materialise because of our emissions to date. This means farmers will need to adapt their methods in order to keep growing maize in a warmer climate.
One approach is to breed new varieties of maize to make them better suited to higher temperatures.
Developing new crop varieties requires crossing two existing types together. This keeps many of the attributes of current varieties that farmers or consumers like – such as colour, taste and size – while adding new climate-proof characteristics, such as heat or drought tolerance, from varieties that grow in other parts of the world.
But our latest paper, just published in Nature Climate Change, shows that conventional breeding is losing the battle against climate change.
We find that the rate at which temperatures across Africa are increasing is outpacing the rate at which new maize varieties can be developed and deployed.
This may sound surprising, since changes in average temperature can be thought of as happening gradually, relatively speaking. However, breeding a new variety takes upwards of six years, then there is national testing of the variety, getting it to market, and encouraging farmers to adopt it. The average time taken to accomplish this for maize in Africa is 18 years, but can be as long as 30 years.
The upshot of this is by the time a new crop variety gets to farmers’ fields, it will be growing in temperatures higher than those it was developed for. As a result, the crop will mature more quickly and have less time to produce grain – and hence provide lower yields.
So, if breeding is to keep up with climate change, something needs to change. Our paper outlines three main ways to tackle the problem.
An obvious, but challenging, option is to speed up the time to breed, test and deploy new varieties.
There are numerous ways to do this. For example, improving links between institutions across the world could see better collaboration on selecting and sharing crop genes. At the other end of the process, improving awareness of new crop varieties can help encourage farmers to grow them once they’re deployed.
A second option is to breed crops in greenhouses at higher temperatures to match the future climate they would be grown in. But, for a new crop variety to be effective for farmers, we need to get that temperature right. Too low, and the new crop variety could mature too quickly in a warmer world, bringing in a low yield. Too high, and the crops could mature too slowly, and wouldn’t be ready to harvest within the growing season, or could suffer from drought after the rains have passed.
Our paper calculates the temperature to maintain during crop breeding that gives the best chance of success in the climate in which it eventually will be grown. Our results suggest that 0.5C above the temperature in which they would otherwise have been bred is a sensible temperature rise to use.
The last option we look at is stringent mitigation. If greenhouse gas emissions are cut, we can limit how much warming crops will be exposed to in the future.
You can see the difference that mitigation makes in the maps below. They show the projected hastening of crop maturing in days per year in sub-Saharan Africa, from 1995 to 2050, according to four different emissions pathways.
The pathways, as used by the Intergovernmental Panel on Climate Change (IPCC), range from RCP2.6, where emissions are curbed to keep global average temperature rise to below 2C above pre-industrial levels, to RCP8.5, where emissions continue to increase and temperature rise is likely to hit 5C by 2100.
The orange and red shading show where crop maturity dates would be most affected by rising temperatures. You can see that the impacts are much more pronounced for RCP8.5 where emissions are not curbed, with up to 4 fewer days per decade for growing maize up to 2050. Under RCP2.6, the impacts are much less severe, with up to 2 fewer days each decade.
Clearly, mitigation is a necessary option if we want to limit the long term impacts on crop yields. But given the time it would take to slow current warming, it is not one that will help us immediately, so we need options in the short-term as well.
A potential fourth option, which we didn’t look at specifically in our study, is the use of genetically modified (GM) crops. This is very different from the conventional breeding process we have been discussing.
Where conventional breeding shares desirable traits between crops of the same species, genetic modification can take genes from one species and manually implant them into the genetic code of an entirely different one. A classic example is golden rice, which gets its colour from the beta carotene gene taken from carrots, and thus adds vitamin A to people’s diets.
It is tempting to think that GM can save the day here, by short-cutting the selection and breeding of new varieties. However, whether you use conventional breeding or GM you still have to get the varieties tested and out in the fields. These stages take 40-60% of the total time, so GM alone will not solve this problem.
It is likely that we’ll need a combination of the options outlined above, rather than just relying on one. Our analysis suggests that whichever combination we select, the changes need to be almost immediate to have a significant impact, since we will to wait 10-30 years to see the benefits of that change.
But this should not be mistaken as yet another clanging bell of climate change doom and gloom. The unavoidable fact is that climate change is creating a mismatch between the crops we grow and the conditions that they grow best in. There are things we can do to fix this. Whilst some efforts are already underway, it is the urgency of the need that has become particularly clear.
The challenge is significant, and not only for Africa. Warming is occurring across the globe. And since most of the crops consumed worldwide have a similar response to warming, the challenge also goes well beyond maize.
Main image: A staff member carries out hand pollination of maize on CIMMYT plots at the Kenya Agricultural Research Institute’s (KARI) Kiboko Research Station. Credit: International Maize and Wheat Improvement Centre via Flickr.
Challinor, A. J. et al. (2016) Current warming will reduce yields unless maize breeding and seed systems adapt immediately, Nature Climate Change, doi:10.1038/nclimate3061