The projected changes in climate around the world are for general increased atmospheric CO2 concentrations and consequent temperatures associated with varied scenarios of less (e.g., Australia) and more (e.g., USA) precipitation. The extent and magnitude of such projections differ around the world, but some examples from Australia, India, Africa, and South America show the general trend, but with variability among locations and regions within continents.
In Australia’s southern wheat belt, average temperatures are projected to increase in all seasons. The result will be more hot days and warm spells and fewer frosts. Trends of decreasing winter and spring precipitation are projected, but there is no clear signal with regard to changes to summer and autumn precipitation. Increased intensity of extreme precipitation events is projected [27
In India, climatic variability and monsoon strength is expected to increase over much of Asia in the 21st century [42
]. Seasonal mean precipitation is expected to increase from the East and South Asian monsoons while the change in other monsoon regions is less certain.
Temperature projections for Africa suggest increases ranging from about 2 to 4 °C for mid-Century, with southern Africa being particularly negatively impacted under the IPCC RCP8 more extreme scenario. Precipitation projections are far more uncertain, but suggest that southern Africa will face declines of up to 20% while there will be increased precipitation in eastern and West Africa. Maize is particularly vulnerable to high temperature and drought at flowering, and simulations suggest that yield would be reduced by >20% for a 1 °C increase in temperature above 20 °C under drought [2
]. Likewise, other grains, such as millet and sorghum, will be reduced by 10–30% and variability increased by 2031–2050 [58
]. These general effects mask considerable diversity in responses among agro-ecologies or mega-environments, with for example highland systems benefitting from warmer temperatures while both wet and dry lowlands are negatively impacted [59
Temperature projections for South America and Amazonia forecast increases of 0.6–2 °C or 3.6–5.2 °C for mid-21st century depending on the scenario (RCP2.6 and RCP8.5, respectively, Figure 10
). For late 21st century, increases of 2–4 °C are projected for the southeast of the subcontinent [60
] as well as warmer nights by 6–12% [61
]. While there is less agreement among meteorologists about precipitation projections (Figure 10
), increases (of 15–20%) have been consistently forecasted for Southeast and western Amazonia and the northwest of Peru, while lower precipitation (10–30%) is projected for the western area of the Andes in Peru and Chile, eastern Amazonia, and northeast and central eastern Brazil.
3.2. Cereal Productivity
Future cereal yields are dependent on temperature and precipitation scenario, the effects of CO2 fertilization, and adapted crop production strategies. Crop models, all with limited skill to predict growth and yield in higher temperature and CO2 concentration than now exist in individual locations where they have been developed, are the only tool with which to make projections. A focus on a single component, such as temperature response, reduces the applicability of current projections.
At the global scale, projected trends of increasing temperatures and elevated CO2
concentrations will have negative impacts on wheat yield globally [3
]. In that comparison using 30 different wheat models to simulate wheat productivity, the authors concluded that wheat yields would decrease 6% per 1 °C rise in temperature and become more variable in both space and time.
Projections for China made by applying SRES A2 and B2 climate scenarios from PRECIS3 using the CERES crop models suggest that rain-fed wheat, maize, and rice yields in China will decrease on average by 11.4–20.4%, 14.5–22.8%, and 8.5–13.6%, respectively, by 2050 if the current technologies remain in use (which is unlikely). If irrigation water is guaranteed, then the output of three major cereal crops will be reduced less, by 2.2–6.7%, 0.4–11.9%, and 4.3–12.4%, respectively [62
]. However, the supply of irrigation water cannot be guaranteed so the likely effect must be more pessimistic even with the positive effects of atmospheric CO2
]. Without adaptation, per capita cereal production is expected to fall in all cases by up to 40% of the current baseline (1961–1990) [63
Analyses for Australia by Innes et al. [64
] using a combination of experimental results coupled with simulation models have projected wheat yield reductions of 5.3% yield per 1 °C. These are consistent with the global analysis by Fischer et al. and Asseng et al., but vary in different locations [1
]. Wheat production occurs over much of the United States but predominantly occurs in the temperate regions of the southern Great Plains (Oklahoma and Kansas) to the northern Great Plains (North and South Dakota) and shows differing yield trends. Warming temperatures have already begun to decrease United States wheat yields in Kansas as observed by Tack et al. using historical yield and meteorological data [65
]. Their regression analysis used a combination of freezing and warming impacts and revealed a 40% reduction in wheat yields with a 4 °C temperature increase and found the newer cultivars were less resistant to heat stress above 34 °C than older cultivars, suggesting that selection of newer cultivars by producers to offset climate impacts may not be effective. In Oklahoma, yield has decreased by 45 kg ha−1
since 1998 while it has increased by 63 kg ha−1
in North Dakota. Differences in climate trends explain these yield responses, but a finer resolution of yield data at state or province level relative to climate is needed to better evaluate where changes in production will occur. For example, yields of winter and spring wheat in the Pacific Northwest states have undergone slight declines of less than 10 kg ha−1
since 1998, but based on crop models that incorporate effects of CO2
they are projected to increase or remain stable to 2090 under RCP 8.5, depending on specific locations, based on downscaled climate projections [66
]. Asseng et al. projected an approximate 3% reduction in wheat yield per 1 °C increase in temperature for North America, notably less than the global average [3
Continuing productivity of wheat and small grain systems under climate change requires attention to current cereal production regions so that new cultivar-management options can provide the basis for adaptation, but equally there is the issue of extending cereal production into regions that may become more climatically suited to these crops. At the same time, however, some current cereal production regions will likely be lost [58
]. One recent study of transformational change (i.e., moving out of one crop or out of agriculture altogether) in Sub-Saharan Africa [68
] suggests that three out of nine major food crops will be significantly affected. Under RCP 8.5, maize and banana will have ~30% of their area transformed while for beans it is >60%. For maize, about 60% of the area will remain suitable and 40% requires transformation to millet or sorghum. Only a very small area, about 0.5% or 0.8 Mha, would have no substitute crops. Modelling together with experimentation plays a major role in understanding and managing such land use change, but while attention must be directed to individual locations, results from only a few representative locations may be misleading. Although crop modelling is an appropriate methodology for the analysis of the effects of climatic factors on crops, there are limitations related to the treatment of extreme temperature and the site specificity of many analyses. Despite the wide range of temperature environments where wheat and small grains are grown, current models lack adequate treatments of extreme temperature events such that more experimental work and model modification is a priority [69
]. While the use of representative sites provides a practical scheme for analysis, many modelling examples are restricted to single sites. The validity of representative sites is still an issue of scale that the latest Agricultural Model Intercomparison and Improvement Project (AgMIP) is yet to address.
There are many challenges to overcome in the quest for increased crop productivity in individual regions. An important consequence of climate change for wheat production systems will be changes in land use. This is well-illustrated in the global study of Ray et al., in which future trends in crop yields were shown to stagnate, increase, plateau, or decline depending on location. For example, in Chile wheat is cropped from 35–40 °S but projections suggest that it and other crops will contract southwards (38–40°) [71
]. Changes in land use are also predicted in other countries by the main producers of maize, rice, and wheat. A lower grain yield of maize is expected, especially for northeast Brazil, and as a consequence a decrease in area sown to maize of 8.5–14% is projected for the whole country [47
]. Positive changes are projected for rice in the southeast of South America (East of Argentina, Uruguay, and South of Brazil), where increases of grain yield up to 28% are predicted by using simulation models [72
]. At present, soybean, maize, and wheat are the main crops sown in this area. One large Australian study [73
] relied on modelling analyses from the town of Birchip to develop an expected response for the entire Victorian wheat belt. While that location can be considered typical of present day Victorian crop yields, the analysis did not consider the possibility of cropping moving to non-traditional cropping areas less than 200 km south near the city of Hamilton and the regional center of Warrnambool. A spatial analysis (100 m grid across Victoria) using a validated catchment wheat model [74
] has shown a likely increase in wheat yield until 2070 in much of that region with adapted cultivars in contrast to yield decreases projected for Birchip by Anwar et al. [75
]. While the spatial study of O’Leary et al. still attracts criticism because it shows potential yield increases outside the major wheat-growing regions of Victoria, it nevertheless shows the impact in response to adaptation of a potentially important trend [74
Another important limitation of currently available methods is that field experiments and modelling analyses do not incorporate social, economic, regulatory, and administrative issues facing farmers and affecting farming practices. Farming combines crop and animal production within a complex socio-economic system such that proposals to advance the productivity of individual components must be tested on real farms under real conditions and the trade-offs understood [76
]. While the need for this comprehensive assessment is acknowledged by research and farming organizations [77
], the high cost and lack of funding make progress slow and fraught with potential failure. To compound the problem, there is a notable trend in developed countries for the general public and policymakers to undervalue science [78
]. Without independent confirmation of our research, how can farmers be assured of success in adopting new practices? Present resources and investment into agricultural research in many developed countries, such as Australia and the USA, are inadequate for the task of meeting future global food demands [5
]. More attention to the economic management of farming is needed because farmers in developed societies farm to meet economic objectives not for family food supply. However, even in developing countries where household food security is the priority, economic considerations are still key as farmers have limited capital to invest in technologies to increase yield. This points to a disconnect between the noble goals of increasing global food supplies and ensuring financial viability at the farm level.
While the call for more collaborative work is continually made, a more determined approach is needed [10
]. Several studies from India are consistent with outputs from cropping system models [3
] that project yield reductions of 10–40% by end of century unless adaption begins now, despite the beneficial effects of increased CO2
]. These studies do not include the effects of pests and diseases and changes in irrigation availability that could further impact crop production. The projected increase in drought and flood events in South Asia could result in greater instability in food production and threaten the livelihood of farmers. In general, most such studies assume no new technology development and no or limited adaptation by farmers. The situation may therefore be more positive if projections include progressive adaptation and smart-adaptive behaviour of farmers and other stakeholders.
Abundant literature is available for South Asia indicating technological, institutional, and policy interventions that can help farmers adapt to climate change as well as to current and future weather variability [84
]. These include simple adaptation practices, such as changes in planting dates and crop cultivars. Additional strategies for increasing adaptive capacity include bridging yield gaps to augment production, deployment of weather tolerant cultivars and diversified land use systems, the use of solar power for irrigation, and assisting farmers in coping with current climatic risks with weather-linked value-added advisory services, crop/weather insurance, and improved land and water use management and policies.
It is also interesting to note that most of the proposed adaptation options include large mitigation co-benefits. The CGIAR’s CCAFS program is scaling out the Climate-Smart Villages (CSVs) model in South Asia to promote a broader climate-smart agriculture [89
]. These villages are sites where a portfolio of the most appropriate technological and institutional interventions, determined by the local community, are implemented to increase food production, enhance adaptive capacity, and reduce emissions. Interventions are customised to each village, but the concept lends itself to application in any region under individual circumstances. Initial results suggest a large potential to maximize synergies among different interventions. CSVs are also being implemented in East and West Africa with good opportunities for cross-regional learning [90
Over the past few decades, national and regional governments have taken several policy and institutional initiatives to buffer agriculture from climatic risks. These include development and diffusion of adapted cultivars, development of contingency plans to manage region-specific risks, establishment of national food buffer stocks, crop insurance, and disaster relief. Although these initiatives have helped to reduce the impact of weather at an aggregated scale, significant problems persist at the local/regional level. To increase local benefits, a clear understanding is required of adaptation practices and technologies and the development of appropriate “business models”. Crop insurance is one such strategy provided immediate benefits to local farmers are guaranteed. Simultaneous efforts are needed to address the complex problems of widespread poverty, poor governance, weak institutions, and human capital that have reduced the full potential of various adaptation practices. This is particularly true in Sub-Saharan Africa, where infrastructure is poor and policy and institutions are weak. Improvements in technologies, institutions, and policies in that region will play an important role into the future [91