Guest Post: The meat to lentils myth

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The current call to eat lentils not meat sounds like a simple way to save the plant from global warming.  Like many simple solutions to complex problems its not quite so simple. If you change from a meat based diet to a plant based one you may be doing more harm to the planet than good.
Our Dairy, beef and sheep production is grass based. Grass pasture is sown down and then maintained for between five and ten years. After that time production tends to decline so pasture is renewed. This is normally done by killing the old grass and weeds and then sowing new pasture. Cultivation and sometimes chemicals are used in renewal.
If we grow lentils, cabbages or grain these crops need to be sown each year, they are all annuals, typically sown in the spring and then harvested in summer or autumn.  Over the winter a cover crop is grown to stop nitrogen and fertilizer leaching. The soil needs to be cultivated. With current technology this means tractors and trucks powered by diesel motors.

 To sow a crop an average of 70 litres of diesel per hectare is burned for cultivation and seeding. This fuel is converted to carbon dioxide at a rate of 2.6kg of carbon dioxide for every litre burnt. Harvesting is also energy intensive with typically more than 20 litres per hectare burned.   Each crop cycle releases 230kg of carbon dioxide, because we do two seedings a year over 400kg of carbon dioxide goes into the atmosphere each year.  Pastural farming with grazing animals has much lower CO2 emissions from cultivation.

If we replace the crop with cows, at three on the hectare each cow will produce about 100kg of methane a year or 300kg per hectare. This is equivalent to between 6,000 and 10,000 kg of CO2 per hectare. It’s not looking good for the cows but life is not that simple.

The methane produced by the cows breaks down into CO2 and is absorbed by the grass that feeds the cows. The methane from the cows reaches an equilibrium in the atmosphere. The carbon dioxide from producing lentils builds up and increases over time.   

In the short term the lentils win. In the long term not so. After about 10 years the amount of methane in the atmosphere will stabilise at about 40.000kg, of CO2. After 25 years still 40,000kg from the cows, but now 10,000kg from lentils.  After 100 years 40,000kg from the cows and 40,000kg. from the lentils. Beyond this greenhouse gas effect from lentils is worse than from cows. 

If you want a short term feel good fix sure stop eating meat and dairy products. If you want the world to be here for your grandchildren maybe you need to think again.

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