Every degree of global warming will reduce the average worldwide yields of four key staple food crops by between three and seven percent is the key finding of a wide-ranging meta-analysis of existing climate-change models, statistical regressions and experimental studies.
The 29 researchers, who published their findings as a paper in Proceedings of the National Academy of Sciences in August 2017, took a broad overview of agricultural research, including the findings of previous studies, and various models and analyses of the likely impacts of climate change on the world’s most important staple food crops.
Two-thirds of the human population’s total caloric intake consists of products made from wheat, corn, rice and soybeans. Each of these staple crops reacts differently to rising temperatures, and these reactions also vary, sometimes significantly, from location to location. On average, however, the meta-analysis shows that we can expect the yields of staple food crops to drop by 3.1 to 7.4 percent with each additional degree Celsius of warming.
The researchers examined only the direct impacts of rising average temperatures on staple crop yields, but acknowledge the potential additional impacts of indirect factors such as:
- drying of soils;
- plant water stress;
- more frequent extreme heat events (‘heat waves’); and
- how changes in climatic conditions might impact the patterns and proliferation of various crop pests, weeds and diseases.
Why are these findings significant?
The findings of the meta-study support predictions made recently by the Intergovernmental Panel on Climate Change about climate’s impacts on food production.
The United Nations’ latest prediction is that the global population will reach a staggering 9.8 billion by 2050, up from 7.6 billion today.
On 2 August 2017, Climatewire reported that:
- temperature rises leading to warmer conditions across the food-producing regions of the world could make it more difficult to grow sufficient amounts of food to keep nearly 10 billion people alive and healthy; and
- that the crops that are able to grow in these changed environmental conditions may contain fewer nutrients, exacerbating any global food shortage.
The signatories of the Paris (COP21) climate agreement have committed collectively to allowing an average global temperature rise of less than 2 degrees Celsius by the end of the 21st century. Despite the White House’s plans to abandon its pledge to the agreement, most of the developed world – including many individual US states and corporations – and many developing nations are, at least in theory, on board.
The study found that the yields of staple crops across the US would be likely to suffer disproportionately with warmer temperatures.
Corn, say the study’s authors – and particularly that grown across the US – will likely suffer significantly lower yields for every extra degree Celsius of temperature rise experienced.
The meta-study showed that of the four staple grain crops examined, corn would be most sensitive to rising temperatures, with evidence suggesting that corn harvests across the world could decline by an average of 7.4 percent for every degree Celsius of warming, and this effect emerging consistently across all major corn-producing regions.
US growers, stated the paper, would be likely to experience the largest drops in productivity, with a predicted average reduction of 10.3 percent in corn yield per degree C of additional warming.
The research suggested that corn harvests in China, Brazil and India would also suffer substantial yield losses with every degree of warming; however, statistical modelling showed that corn-growers in France might be looking forward to modest improvements in yield with warmer temperatures.
Wheat and rice
Worldwide wheat yields would likely decrease at an average of six percent per degree C of warming, with this level of decline consistent across the globe, the meta-study found.
Rice, a staple food for the people of many developing nations, could experience yield reductions of an average 3.2 percent per degree of warming, with some research suggesting impacts of up to 6 percent, and statistical regression analyses indicating almost zero yield decreases in rice-growing regions.
In soybeans, the fourth-most important commodity crop on the planet, the study predicted average yield losses, globally, of 3.1 percent with each degree of warming, though this estimate had a higher level of uncertainty.
The researchers estimated that 1 degree of warming could cause yields of American soybean crops to decrease by an average of 6.8 percent, but concluded that soybean harvests across Chinese growing regions might see no significant changes with this level of temperature rise.
According to the paper’s authors, yields of staple food crops have already started to decline across some regions of the world.
“Further increases in temperatures will continue to suppress yields, despite farmers' adaptation efforts,” they stated.
SOURCE E&E News, via Scientific American.