food production and the food chain: the main numbers: solar radiation impacting on earth –178,000...
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Food production and the food Food production and the food chain:chain:The main numbers:The main numbers:
• Solar radiation impacting on Earth– 178,000 terawatts (a terawatt is 1012 watts) annually
• Capture of this energy by plants and algae (both terrestrial and marine)– 100 to 120 terawatts annually
• 6 terawatts on arable land
• 12 terawatts on grassland or savanna
• 50 terawatts in forest
• Question:– What can we therefore say about plant productivity in terms of its ability
to supply the total energy used by humankind?
Food production and the food Food production and the food chain:chain:The main numbers:The main numbers:
>120,000 terawatts
~ 55,000 terawatts left
~ 40,000 terawatts inHydrological cycle
Of which 0.01 - 0.1% “could” be captured by hydro
Global energy consumptionby man: 15 terawatts
Capture by plants: 120 terawatts
Food production and the food Food production and the food chain:chain:Photosynthetic conversion by plantsPhotosynthetic conversion by plants
• Photosynthetic conversion by plants– More energy is landing on the plant than is captured by it.– 3-6% of incoming solar radiation impacting on the plant is captured.– Perhaps 1/3 to 1/5 of this is stored by the plant (grain, tuber, stem, root
etc.) giving an overall conversion efficiency of about 1%.
• The hidden energy needed by plants– Approx 1000kg of water is transpired for each kg of biomass produced by
a plant. This energy also comes from the sun via the hydrologic cycle.– The solar energy from the hydrologic cycle needed to produce this
transpiration is more than 100 times the energy contained in the plant biomass.
• Question:– In terms of the energy required by a plant to produce biomass, which is
greater; photosynthetic or hydrologic?
What proportion of total energy What proportion of total energy consumption is actually used in food consumption is actually used in food production?production?
• Global energy consumption by man– 15 terawatts (~475 exajoules)
• Direct Agricultural use:– Only 1-2 % of this globally (e.g. ~1.2 exajoules in USA)
• Question:– What can we say about total plant productivity and its ability to
provide energy used in primary agriculture?
How does global food How does global food requirement compare with requirement compare with photosynthetic output?photosynthetic output?
• Each human requires about 10MJ of food energy per day
• This is about 22 exajoules planet-wide per year• On an annual basis this is currently equivalent to 0.7
terawatts• Or less than 1/20 of total global energy use by humans• Or ~0.7% of global photosynthesis• Or ~12% of the photosynthetic product captured by
plants on arable land worldwide
How much of the World’s How much of the World’s photosynthetically active land base is photosynthetically active land base is agricultural?agricultural?
• Total land:– 13 billion hectares
• Agricultural land– 5 billion hectares
• Arable: 1.5 billion ha (potentially more productive)
• Grassland: 3.5 billion ha (for feeding animals which we can then consume)
• Question:– Where does this leave agricultural capacity in terms of its ability
to produce enough food now and in the future?– To answer this we need more information
Photosynthetically active land Photosynthetically active land base and soil degradationbase and soil degradation
Enough food for now and into the Enough food for now and into the future:future:PopulationPopulation
• Current world population:– 6 billion
• Projected population for 2050:– 7.7 (L)– 9.4 (M)– 11.2 (H)
• Question:– Assuming medium growth, how much more food will be required
by 2050?
Enough food for now and into the Enough food for now and into the future:future:DietDiet
• Global food requirement expressed in grain equivalents (billion tons d.w. per year).
• Vegetarian diet– Today’s population: 2.9– 2050 (M): 4.5
• Moderate diet– Today’s population: 5.2– 2050 (M): 8.2
• Affluent diet– Today’s population: 9.1– 2050 (M): 14.4
• Question: How does this compare with current food production?– Answer: 4.5 currently
What is the potential food What is the potential food production?production?
• If all current agricultural land were operated using maximum inputs (including irrigation), to a level equivalent to the most productive European fields:– Then (theoretically) actual productivity could be ten times higher than
now
• If potentially productive non-agricultural land were brought into agriculture, this would increase by a further 50%
• Even using low inputs, potential agricultural productivity could be four times higher than now.– But if this potential is there, why is there no sign of it being realized?
Need for food: Theory Need for food: Theory versus practiceversus practice
• From slide 5:– 22 exajoules needed (in theory) to feed current population
• In reality, more is needed, to allow for waste, after-harvest losses, distribution inequalities etc.
• From slide 9:– 4.5 billion tons grain equivalent of food produced each year.
– Very broadly, this equates to 45 - 60 exajoules annual production.
• So currently, at least twice the theoretical need is being produced to feed World population.
• From slide 2: – Energy capture on agricultural land: 500 exajoules
• Existing productivity is much lower than indicated on slide 2.
Efficiency in food: Efficiency in food: Developing versus Developing versus developed World?developed World?
1999 data for World energy use, energy use in primary agriculture, and food energy produced (at consumption point).
Total energy use
Energy use in primary agriculture
Food energy produced
Energy efficiency
World 300 EJ 7 EJ 25 EJ 1:3.5
Developed countries
175 EJ 3.7 EJ 6 EJ 1:1.6
Developing countries
125 EJ 3.2 EJ 19 EJ 1:6
And what of energy used in And what of energy used in food; is this sustainable?food; is this sustainable?
Energy required to produce food in a Western society (1990)
Item of energy use MJ/person/day % of total
Used on the farm 6MJ
Farm inputs 8MJ
Processing 26MJ
Transport to market 20MJ
Wholesale and retail 15MJ
Used in the home for food 25MJ
Total 100MJ 100
Energy contained in food eaten 10MJ
So if the whole World moves to an So if the whole World moves to an affluent diet and high input affluent diet and high input systems, do we have enough fuel?systems, do we have enough fuel?
• From slide 5:– 22 exajoules needed (in theory) to feed current population
• But, if everyone on the planet needed 10 units of fossil fuel energy for each unit of food energy we consume, then the real energy need is 220 exajoules
• And, if everyone on the planet over-fed themselves to the extent that Western society now does, then the real energy need rises to 330 exajoules
• And if the population increases by 50%, this brings the total energy need to 445 exajoules
• Question:– Is there enough fossil fuel for this?– Could biofuels be the answer?
Is there enough fossil fuel; how Is there enough fossil fuel; how much of current fossil fuel use is much of current fossil fuel use is devoted to food production?devoted to food production?
• Assume 450 exajoules (EJ) of fossil fuels are needed for food production, distribution etc. in a year (i.e. everyone follows the western model)
– This is in excess of current total energy from oil extracted annually (which is about 150 EJ per year)
– Energy from gas constitutes 100 EJ per year– Energy from coal contributes an extra 125 EJ per year– Renewables and nuclear contribute another 60 (about 50/50)
• However, remember that right now 80% of fossil fuel use in the developed World is not used for food production or the food chain.
• If this rate were applied to the figures above, then 2000 EJ per year would be required for World use; more than four times the current use.
• Compare this to the current figure of 90EJ fossil fuel used in the food production system.
Is there enough potential biofuel?Is there enough potential biofuel?
• Large variations in estimates of biomass biofuels:– IPCC (2000) 334million ha @ 24t/ha/yr. = 107 EJ/yr.
• (assuming 18MJ/kg dry matter)
– Higher estimates pre-date this one, mostly based on more available land, but lower yields.
– The IPCC yield estimate seems very optimistic.– The amount of land available for biofuel could be increased by
making existing farmland more productive.• However, this typically requires further energy inputs.
This is just energy This is just energy sustainability – what about sustainability – what about other considerations?other considerations?
• Water depletion– Water from many aquifers is being used more quickly than it is being
replaced.
• Water pollution– Groundwater contamination with fertilisers, agrochemicals.
• Tolyfluanid plus ozone treatment creates nitrosamines• Glyphosate in ground water• Simazine
– 45% of wells in potato and fruit growing area of Portugal
• Soil erosion– The dust bowl
• Atmospheric pollution
• CO2 and climate change
• Destruction of habitats
Some examples…
‘Dust Bowl’ USA 1930’s
NOAA Photo Library
500,000 homeless
‘environmental refugees’
CO2 in the atmosphereCO2 in the atmosphere
Carbon flowsCarbon flows
1 petagram = 1 billion tonnes
Integrated into an Ecological Integrated into an Ecological footprintfootprint
Kitzes et al. 2008. Shrink and share: humanity’s present and future ecological footprint. Phil. Trans. R. Soc. B. 363, 467-475.
Ecological footprint: why the Ecological footprint: why the Western World needs to actWestern World needs to act
Kitzes et al. 2008. Shrink and share: humanity’s present and future ecological footprint. Phil. Trans. R. Soc. B. 363, 467-475.
Silver bullet: What about Silver bullet: What about new food production new food production technologies?technologies?
• The current proposition is that GM technology may lead to the next “great leap forward” in plant productivity
• Thus far, despite 20 years of trying, GM crops produce lower yields than conventionally bred.
• GM crops modified to resist herbicides have resulted in significant increases in herbicide usage.
• Environmental damage due to GM technology and the monocultures it promotes has been reported, but not studied in depth.
• Like any technology, genetic modification of plants can be used for the benefit of many or few. The privatisation of this technology via plant patents and de-regulation has meant only benefits for the companies involved, and not for humanity.
