Meet Daisy the cow – global climate’s enemy number one.

Newsnight

When I started to investigate the impact of food on the environment a month ago I thought I would find myself fretting over food miles. In fact transport is a tiny component of agriculture’s worldwide contribution to greenhouse gas emissions.

No, the main culprit is out there in the fields, chewing her cud. It turns out that livestock – predominantly cattle – are responsible for an astonishing proportion of global warming gases - 18 per cent of the total, to be precise.

That’s right, almost a fifth of all emissions which is more greenhouse gas emissions than all the transport on earth – planes, trains, cars, skidoos the lot.

You’ll be wondering how I reach that staggering conclusion. Indeed, regular readers of this blog may be worried that my decision forgo flesh and become a vegan during January has fostered an irrational hatred of animals.

Not so. The research implicating Daisy and her bovine brothers and sisters in global warming is very well sourced. A good start is “Livestock’s Long Shadow”, a report by the United Nations’ Food and Agriculture Organisation.

So why is the meat we eat so polluting?

Well, first of all we need to get a sense of scale. Seventy per cent of all agricultural land is used to raise animals – that’s a third of the land surface of the entire planet. What’s more, over a third of all cereal production goes to feed those animals.

The UN report estimates that 160 million tonnes of carbon dioxide are associated with the fossil fuels emitted by this vast global industry – that’s roughly a third of the UK’s total CO2 emissions. The figure includes transporting meat and dairy products across the globe, as well as the carbon dioxide emitted on the farm, in processing and in manufacture of nitrogen fertiliser, which is used to raise crops for feed for animals.

Add in the carbon from deforestation and land degradation and the figure is far, far higher. Most deforested land is used for pasture and the UN reckons the carbon released in the process takes the carbon cost of livestock up to the equivalent of 2.7 billion tonnes of carbon dioxide. That’s around seven per cent of all the greenhouse gases emitted by man.

That is a lot of global warming gas but still way short of that eighteen per cent figure. That’s because carbon dioxide isn’t the only global warming gas that animals are responsible for – which is where Daisy comes in.

Ruminant animals like cows and sheep produce a lot of methane as they digest their food. And methane is a powerful greenhouse gas – twenty three times as powerful as carbon dioxide, in fact.

There are reckoned to be around one and a half billion head of cattle on the planet and one point seven billion sheep. They, together with the more modest emissions of other farm animals, produce 37 per cent of global methane emissions which adds up to the equivalent of another 2.2 billion tonnes of carbon dioxide a year.

We’re still not at a fifth of global emissions though. To get there you have to factor in the effects of another global warming gas - nitrous oxide. It is way more potent than even methane with 296 times the global warming power of carbon dioxide. Sixty five per cent of human related emissions of nitrous oxide are from the nitrogen in animal manure. That accounts for the equivalent of another 2.2 billion tonnes of carbon dioxide.

Add the effects of the three gases associated with farming animals and you get total emissions equivalent to 7.1 billion tonnes of carbon dioxide a year. According to the UN report we humans are responsible for a total of the equivalent of 40 billion tonnes of carbon dioxide a year. That’s where I got that incredible figure of 18 per cent of total emissions.

Which brings me back to my experiment in veganism. The reason I suppressed my carnal desires throughout January was to find out what difference cutting animal products from my diet would make to my so-called carbon footprint.

As usual, my carbon guru Professor Tim Jackson has been on the case. He calculates that eighteen per cent of the carbon emissions created by the average diet are from meat and a further ten per cent are from dairy products.

But, as should be apparent from this blog, only counting carbon dioxide would be a woeful underestimate. The problem is no-one has calculated the contribution methane and nitrous oxide emissions make to the climate cost of the food we eat. Professor Tim reckons it is safe to double the figure for carbon dioxide which means sixty per cent of the global warming potential of the average diet is from animal products.

Does that mean we should all be going vegan?

If animal products account almost two thirds of the greenhouse gasses associated with food are from animal husbandry that is surely a powerful argument for any aspiring ethical man or woman to go vegan. But does a vegan diet give you all the nutrients you need?

I felt great not eating meat and a Bupa health-check at the beginning and end of my experiment showed that I shed two kilos in thirty one days, cutting my body fat from 19 per cent of my weight to just 15 per cent.

I also saw my cholesterol level plummet from 5.6 mmol/L (rather high) to just 3.4 mmol/L (very low for a man of my age). The problem is that there are two types of cholesterol – a good one and a bad one – and in my case both fell. Not only that my haemoglobin levels fell to just above the acceptable level because, the doctor told me, I was almost certainly not getting enough vitamin B12 and iron.

Which is why, when I finally broke my vegan fast, I chose one of the finest steak restaurants in London. I judged that only a very large slice of Daisy could make up for my missing nutrients.

One feast of flesh aside, I’ve resolved to eat less meat but the rest of the world isn’t going to. As incomes rise meat is one of the first things people buy. Meat consumption is to double by 2050.

So if, like me, you are going to continue to eat animals you might consider another way of reducing the environmental impact of your food – actually eat the stuff you buy. A quarter of all the food that is produced goes uneaten - most of it growing mould at the bottom of a fridge.