Impacts on Food Production

Rice, wheat, maize, and soybean provide two-thirds of human caloric intake. Two degrees Celsius of global mean surface temperature (GMST) warming would result in significant reductions in productivity from these food crops. This is while the global population grows and continues to consume more per capita. Only we will determine how warm our Earth will become. There is still time to save humanity and the world that we know. But we must make choices and implement them quickly.

Food production affected by climate change

One degree Celsius warming is already causing food productivity reductions, and this was not expected. Until recently the consensus was that moderate warming of 2°C to 3°C would benefit global agriculture. These expectations have recently been squashed. A 2019 study assessed the impact of current climate change on yields of the world’s ten most important crops. It found that many of barley, cassava, maize, oil palm, rapeseed, rice, sorghum, soybean, sugarcane and wheat are suffering food productivity reductions. On average these crops have suffered a 1% decrease in productivity. This is reducing calorific availability in nearly half of the world’s most food-insecure countries. Climate-related undernutrition is already causing deaths in poorer countries due to decreased yields¹.

With 3°C warming, increased heat and declining annual rainfall would mean that the world would move into a food deficit. Smaller farms in South Asia and Africa would fail year after year due to drought and heat. This affects the livelihoods of billions of people. Higher latitudes like Canada would not be immune – crops would be affected by intense heat. Some mitigation may come from the ability for growing areas to migrate towards the poles. This will be limited by soils, and by arboreal forests and other ecologically valuable areas – which also absorb CO₂ and are important to offset the need for crop migration in the first place! Read about how fast our planet is warming.

There will be many more deaths from food scarcity in the 2°C world. A paper in the medical journal The Lancet projected that warming of 2°C – expected in their scenario by mid-century – would lead to a ‘relative reduction of global food availability in 2050 of 99 kcal per person per day’ when compared with a scenario with no warming². This would result in reduced nourishment for hundreds of thousands of people, especially (but not only) in poorer countries. The paper found that the impact of 2°C warming on staple crops leads to 529,000 warming-related deaths globally by 2050. This is a death toll that ‘far exceeds other climate-related health effects that are projected to occur in 2050’. At least half a million people will die every year from malnutrition in a two-degree world because of climate change.

It gets worse – this could be an underestimate. The increasing frequency of extreme temperatures that cross critical heat tolerance thresholds for different cultivated species will exacerbate these effects. Maize is the world’s most important staple crop, but is particularly sensitive to drought and heat stress. Maize has a critical temperature threshold of about 32°C while setting seed. Temperatures above this level reduce photosynthesis and increase the amount of water lost from the leaves.

A 2011 paper shows that each day spent above 30°C reduces yield by 1%, and by closer to 2% under drought conditions³. A three-week heatwave could slash yields by 25%! The relationship between warming and yields is non-linear. If the temperature exceeds critical levels for longer or more frequently, yields will decline much more rapidly than you might expect. Farmers in Africa have few adaptation options; water for irrigation is rarely available, and other inputs such as fertiliser can also be scarce and expensive. Even newly developed drought-tolerant maize needs rain.

A recent study, published in February 2019 in the journal Earth’s Future, predicted that once-in-a-decade extreme climate events would become ‘the new normal’ in a 1.5°C-warmer world from about the mid-2020s onwards⁴. With 2°C global warming, ‘maize areas will be affected by heat stress and drought never experienced before, affecting many major and minor production regions’. The United States is the world’s largest producer. The biggest area of concern is the increasing heat stress throughout its Corn Belt. In a world warmed by 2°C, global production would be reduced by as much as 100 million tonnes. This would eliminate most of the world’s maize trade, because producing countries would tend to serve their own demands before exporting. This would be a disaster for importing countries like Mexico and Japan. It would impact meat markets because maize is important for animal feed.

A 2017 paper projected a 10% loss of the United States’ maize crop, 8% losses in China, and 5% in Brazil and India, per degree Celsius of global temperature rise⁵. It is not only maize that is at risk. The same paper also projects a 6% loss of global wheat yield with each degree of global warming. And a 3% reduction in rice. The US is the the world’s largest producer of soybeans – a critically important protein crop. The US can expect to lose nearly 7% of its soybean harvest per degree Celsius. These figures are consistent with other studies. In 2014, Asseng et al also predicted a 6% fall in global wheat production for each degree rise in global temperature⁶.

Scientists also predict that insect crop pests could dramatically multiply with increasing temperatures, seriously affecting harvests of rice, maize and wheat. Yields may be reduced by as much as 25% per degree Celsius of warming due to increased insect attacks⁷.

And while increased CO₂ improves plant growth, this is offset by another impact: higher levels of CO₂ make crops less nutritious. Many food crops will have protein, zinc and iron contents that are 3–17% lower when atmospheric CO₂ reaches 550 ppm⁸. Smith, et al, warned that ‘elevated CO₂ could cause an additional 175 million people to be zinc deficient and an additional 122 million people to be protein deficient’. This would cause hundreds of millions more people to to suffer from malnutrition.

All of this is in the context of increasing world population growth, and increasing food consumption per capita.

Growth in food demand

The IPCC modelled climate change scenarios using shared socio-economic pathways (SSPs)⁹. The five SSPs span a range of challenges to climate change mitigation and adaptation. To illustrate the compounding effect of population growth on food production impacts, only SSP1 and SSP3 are listed here.

SSP1 includes:

• a peak and decline in population (~7 billion in 2100)
• high income and reduced inequalities
• effective land-use regulation
• less resource intensive consumption including food produced in low-GHG emission systems and lower food waste
• free trade and
• environmentally-friendly technologies and lifestyles.

Relative to other pathways, SSP1 has low challenges to mitigation and low challenges to adaptation (i.e., high adaptive capacity).

SSP3 includes:

• high population growth (~13 billion in 2100)
• low income and continued inequalities
• material-intensive consumption and production
• barriers to trade and
• slow rates of technological change.

Relative to other pathways, SSP3 has high challenges to mitigation and high challenges to adaptation (i.e., low adaptive capacity).

The chart below indicates a significant increase in severe impacts/risks and persistence of desertification, land degradation and food insecurity with more then 2°C of warming.

Experts already consider that feeding a much greater world population of 9.5 to 10 billion people by mid-century will be an aspirational challenge. This is without considering the impacts of climate change. Doing so without ploughing up the rainforests and destroying the Earth’s last wild areas is an even greater challenge. The mainstream forecasts call for at least a 70% increase in global food production to deal with these challenges by 2050. It is very difficult to see how this can be delivered in a world suffering simultaneous major yield declines due to drought and heat impacts.

As the caretakers of this planet, only we will determine how warm our Earth will become. There is still time to save humanity and the world that we know. We must make choices and implement them quickly.

References

Ref 1: Lynas, M., “Our Final Warning – Six Degrees of Climate Emergency”, HarperCollins, 2020.

Ref 2: Springmann, M. et al., 2016: “Global and regional health effects of future food production under climate change: a modelling study”, The Lancet, 387: 1937–46

Ref 3: Lobell, D. et al., 2011: “Nonlinear heat effects on African maize as evidenced by historical yield trials.”, Nature Climate Change, 1. 10.1038/nclimate1043.

Ref 4: Zampieri, M et al., 2019: “When Will Current Climate Extremes Affecting Maize Production Become the Norm?”, Earth’s Future, Volume 7, Issue 2

Ref 5: Zhao, C., et al, 2017, “Temperature increase reduces global yields of major crops in four independent estimates”, PNAS, Vol 114 No. 35

Ref 6: Asseng, S. et al., 2014: “Rising temperatures reduce global wheat production”, Nature Climate Change, 5, 143–7

Ref 7: Deutsch, C. et al., 2018: “Increase in crop losses to insect pests in a warming climate”, Science, 361, 916–19

Ref 8: Smith, M. & Myers, S., 2018: “Impact of anthropogenic CO2 emissions on global human nutrition”, Nature Climate Change, 8, 834–9

Ref 9: IPCC, 2019: “Summary for Policymakers. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems” Shukla, P.R. et al., In press.