Food and Nutrition, 2014

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climate change is projected to reduce crop yields … by 3-16% by 2080, with sharper reductions in lower latitudes

For survival, after air and water comes food. There are many factors that will affect global food production between now and 2050. Here just two are illustrated: one – climate change – a major challenge, the other – food waste – giving grounds for hope.

First, climate change is broadly and consistently projected to reduce crop yields, with an average country reduction by 3-16% by 2080, with sharper reductions in lower latitudes. This projection (IMF, 2008) is based on six model variants. Here we show the results (see map) of the most optimistic assumption – that ‘carbon fertilisation’ helps offset other adverse effects of climate change – resulting in an overall 3% reduction.

Carbon fertilisation needs some explanation. Plants need carbon to grow, and is a major part of structure (hence the carbon we burn in wood, coal etc.) and in crops (carbohydrates). Plants get their carbon as CO2 from the air by photosynthesis. Usually other vital nutrients, such as nitrogen (N), phosphorus (P) and/or potassium (K) are scarcer than carbon, and plant growth is constrained by these before they are affected by a shortage of carbon. This is especially so in farming, which is why NPK fertilisers are used. So, it is argued, lack of carbon may limit crop growth. However this is much debated: plants growth may also be limited by other factors. Overall, if carbon fertilisation is a mitigating factor a 3% average reduction for countries was forecast. High latitudes may see a proportional increase in production but with sharp declines in lower latitudes by 2080. But absolute yields in colder climates, with shorter seasons, may be lower.

… this suggests declining food production at a time when … the world expects more

If carbon fertilisation is not significant, according to these models, a far greater and near-universal decline is predicted, resulting in an average per country reduction of 16%. Moreover no account is taken of the impact of more extreme weather. Either way, this suggests declining global food production at a time when — if current western life-styles and diets were more widely adopted by a more affluent world — the world expects more.

Above: Predicted Change in Agricultural Productivity between 2003 and the 2080s This projection, the overall result of six models, assumes that carbon dioxide fertilisation will have a significant mitigating effect on the impact of rising temperatures. Green indicates increasing growth rates, red decreasing rates and grey indicates no information. The detail should not be relied upon, but the broad trends are thought to be robust. Source: IMF 2008

… only 43% of crop energy may be consumed in meat & dairy … over half of all food produced may be wasted by consumers

We may be able to gain ground by reducing food loss. For example considerable food energy is lost through excessive meat and dairy consumption. According to UNEP (2011), of the total energy potentially available in a crop, 13% is lost after harvest, a further 26% in the conversion to meat and dairy products, and a further 17% in distribution and waste. If so, this means that only 43% of the food energy in crops at harvest may be retained when consumed as grain-fed meat and dairy products (see left hand graph). More generally, in developing countries, again according to UNEP (2011), food loss generally comes on the farm and in transportation, processing and retail. But in countries such as the USA over half of all food produced can be wasted once it reaches households and other consumers (below).


 Above: The makeup of total global food waste Left: loss of calories from an edible crop in the steps from harvest to meat and dairy production and then lost in distribution and waste. Right: Huge amounts of food is reportedly wasted in developed countries by consumers. Source: UNEP (2011)

Source: Trends to Bend, modus vivendi, 2014, MMG