The World as We Know It Will End Unless We Change Our Eating Habits - A Case For The Vegan Option Continued.

30/04/2013 12:29 BST | Updated 28/06/2013 10:12 BST

In many parts of the world incomes are increasing and ever more people are moving into cities. Lifestyles are changing. And so are diets.

In China the change to a western diet is growing apace. Western restaurant chains - McDonald's, KFC, Pizza Hut - are making inroads. Already the Chinese are eating one quarter of the world's meat supply.

Indians are also switching to a western diet. Since 1980 their poultry meat consumption has increased by 1000%. Their egg consumption by 224%. Milk by 114%. Pig meat by 135%. And beef and buffalo by 60%.

If this rate continues and if the world population increases from today's 7 billion to a predicted 9.5 billion by 2050 then 120 billion farm animals a year will have to be slaughtered. The current number is nearing 60 billion.

There are those who foresee that this massive increase in livestock production will cause the world as we know it to to end. They forecast severe water shortages. Wrecked ecosystems. The climate changed. Fish stocks depleted. All of which - some say - is scaremongering. But it has already started.

1.7 billion people rely on water from underground deposits. Some are replenishable. Others are not. In so-called 'fossil' aquifers water has accumulated over thousands of years and once depleted it will take thousands more years of rainfall to refill them. This is already happening in China; in the US; in Mexico; Libya; Iran; Yemen; Saudi Arabia; Northern India; and eastern Europe.

Of the fresh water used by humans 8% goes into raising farm animals and most of that is used to irrigate the crops to feed them. As a result 1kg of beef takes 12 times more water to produce than 1kg wheat.

Over half of China's wheat and one third of its corn is grown on the North China Plain. Already the replenishable aquifer beneath it is showing signs of depletion and drilling has started on the fossil aquifer.

In Saudi Arabia the largest dairy in the world - Al Safi Danone - holds 37,000 cows. The company has recently been given permission to extend drilling into the Saudi Aquifer. It is predicted that this water supply will run out in just a few decades.

In the US the High Plains Aquifer is used to irrigate 27% of the US's farm land. Extraction is already exceeding the aquifer's rate of natural recharge and in some places the supply has already run out.

Forecasts have been made that by 2025 64% of the world's population will be living in water-stressed areas. Think of the potential for conflict where aquifers are shared by several countries.

It's a similar story for land. Growing soya, maize and barley to feed farm animals is already taking up 30% of the world's arable land. Overgrazing causes soil erosion and, at worst, desertification. Given that the production of 1kg of beef uses 15 times more land than 1kg of cereals and 70 times more than 1kg of vegetables an increase in our demand for animal products means we will run out of arable land.

One third of the world's fish harvest is used to feed farm animals including farmed fish and prawns. Overfishing is causing the depletion of many fisheries. In the developing world 200 million people depend on fish for their livelihoods and also as a primary source of protein. For them a collapse in fish stocks is particularly serious.

Between 18% and 51% of greenhouse gas emissions (depending on the reports you read) are attributed to livestock production. Methane (from animals' digestive tracts) and nitrous oxide (from animal dung and urine) are notably potent greenhouse gases. And CO2 from fossil fuels used in meat production is - depending on the intensity of agriculture - between 2.5 and 50 times greater than that used, kilo for kilo, to produce plant crops.

Run-off from manure - together with fertilizer and pesticides - contaminates water. The quantity of manure in intensive agriculture - its storage, treatment and disposal - is already becoming unmanageable.

80% of the increase in livestock production is in intensive production systems. By design they are far from natural. With inputs imported and chemical they are the very opposite of traditional farms where, in a natural cycle, feed is grown on the farm, animals roam freely and their dung fertilises the ground. But traditional - extensive - farming is on the decrease. Small scale farmers are losing their livelihoods and their food security is threatened. Meanwhile the world's population increases.

If we use the last of our water reserves. If we run out of arable land. |If fish stocks are wiped out. If we seriously deplete our accessible fossil fuels. Then the world as we know it will end. And as long as intensively farmed animals form such a large proportion of the worlds' diet it seems certain that all these things will come to pass.