We inhale, we exhale. In, out, in, out, inexorably taking in the air around us, processing it through our lungs, into our bloodstream and every cell in our bodies, and then releasing this once again into the air. Sometimes faster - when we are exercising, working or under stress - and sometimes slower - when at rest or relaxed. But always breathing, in and out, at around 12 times a minute, 720 times an hour, 17,000 times a day, 6.3 million times a year. If we stop this relentless cycle of respiration for more than a couple of minutes, we die.

Given this inevitable outcome, it seems sensible to expand on the question "What if we all stopped breathing?" Obviously, if every human stopped breathing then humans would cease to exist and the climate crisis would be solved. At least, as far as we were concerned, there would be no climate crisis because we would not be there to experience it.

But there is another, less obvious reason to ask this question. I was alerted to the issue of biological carbon dioxide only last week when I was handed an article from Saga Magazine profiling James Lovelock, long-term biological ecologist, and sometime student hero of mine. He stated, "People in Britain breathe out five times as much carbon as British industry produces." Clearly this was not a figure to ignore, so I did some calculations.

At rest we inhale about 550ml of air, of which 115ml is oxygen. When we exhale between 3 and 5 percent of that breath - about a quarter of the oxygen - becomes carbon dioxide, about 27ml of this pernicious greenhouse gas. This means that - assuming CO2 weighs 2g/litre - the average resting human produces 170,000 litres, or 340kg carbon dioxide per year. With a moderate level of activity, we can increase this to a conservative 500kg.

British industry (excluding electricity generation) produced 99 million tonnes of carbon dioxide in 2005. 60 million British people produced about 30 million tonnes of carbon dioxide in the same year. Lovelock was out by a factor of 16, but that does not necessarily mean that human exhalation doesn’t matter.

There are 6.5 billion humans on Earth, and this number is rising all the time. In total, these humans exhale around 3.2 billion tonnes of carbon dioxide per year. In 2004 the global anthropomorphic (man made - excluding breathing) carbon dioxide emissions total was 7.9 billion tonnes. Our breathing adds an extra 40% to the global total!

If we were to add this to the total just like that, then suddenly the future calculations of global temperature rise would be dramatically incorrect, and have to be adjusted to take account of the change in the human population. Like it or not, there is nothing we can do to change the amount of carbon dioxide an individual human exhales, apart from ensuring that everyone does little or no exercise. Probably not a great survival strategy.

It would be very easy to say "well, breathing doesn’t matter anyway as it will all be absorbed by the oceans and plants". It is a natural attitude to take when talking about biological, rather than technological emissions. The US Department Of Energy say this:

"This carbon dioxide includes carbon that was originally taken out of the carbon dioxide in the air by plants through photosynthesis - whether you eat the plants directly or animals that eat the plants. Thus, there is a closed loop, with no net addition to the atmosphere. Of course, the agriculture, food processing, and marketing industries use energy (in many cases based on the combustion of fossil fuels), but their emissions of carbon dioxide are captured in our estimates as emissions from solid, liquid, or gaseous fuels"

( http://cdiac.ornl.gov/pns/faq.html)

So is it really a "closed loop", and am I worrying about nothing?

Well, for a start, the DoE recognise that a number of factors do add to the overall emissions - to produce food you need energy, and unless that energy just comes from the sun or volcanic activity, either directly or indirectly, then there will be a removal of energy from the system at some point.

Secondly, humans are efficient, but not perfectly efficient users of food energy. A closed loop system would ensure that nothing enters or exits the system. We know that humans give off a great deal of heat, which is effectively wasted energy; the only potential sources of non-heat energy are mechanical - from human work - and in the reprocessing of by-products. Human work, if devoted to the production of food is certainly one way of keeping energy in the "loop", but may not be the most efficient use of energy possible - more of this later. In terms of human by-products, the use of faeces as a fertiliser will never add a significant amount of energy back into the soil, so the use of additional plant, animal or chemical fertilizers are inevitably required to put energy back into the system.

More importantly, the DoE seems to be distancing the act of breathing from the very processes that they include at the end of their statement, and this - I think - is the key issue.


Many Choices

If we want to travel 20km from point A to point B, then we have a wide range of choices available to us, but for the sake of argument let’s consider the difference between the environmentalist’s 2nd best friend (after leg power), the bicycle, and a typical automobile.

In Europe, the average automobile emits about 170 grams of CO2 for every kilometre. In the USA and Canada this is considerably higher, but let’s take the European average as a starting point. If I were to travel from A to B by car then my vehicle would emit approximately 3.4kg of carbon dioxide. If I travelled at an average of 100kph (about 60mph), then the journey would take 12 minutes, during which time I would not exert myself, and thus personally emit only 8 grams of CO2. The total for the journey would thus be 3.4kg of carbon dioxide, give or take a few grams.

If, instead, I travelled by bicycle, then I would have to exert myself. There is no way I could cycle at 100kph, but can easily reach 20kph, making my journey last 1 hour. When I cycle I breathe at between 20 and 30 breaths per minute, so let’s assume 30bpm, with no increase in oxygen intake per breath. Over that hour of cycling, a person would therefore emit only 100 grams of carbon dioxide, or just 3.4% of the carbon emitted by the combined vehicle and human. If you want to reduce your carbon dioxide emissions then travel slower.

As I said earlier, the way in which food– and thus our personal carbon dioxide - is produced varies in efficiency, vastly so.

Often, the only carbon emissions referred to that relate to food, are "food miles", and there are miles and miles of articles that anyone can read – many of them conflicting with each other. If you want to calculate them yourself then this resource [ http://statistics.defra.gov.uk/esg/reports/foodmiles/annex3.pdf] is as good as any other. The problem with just including "food miles" is that there are so many other factors involved in evaluating the overall carbon (and not forgetting methane and, often overlooked, nitrous oxide) emissions of a person’s food.

One critical factor that I highlighted in an earlier article is the type of food, whether it be plant or animal based. I found that an average of 11kg of vegetable matter was required to produce 1kg of meat. Not only is there a vastly larger amount of fertilizers, forest and transportation required but - as this paper [ http://topsoil.nserl.purdue.edu/fpadmin/isco99/pdf/ISCOdisc/SustainingTheGlobalFarm/P140-HBSo.pdf ] shows - the mere cultivation of land causes a great deal of carbon dioxide to be released into the atmosphere. As this paper also shows, how the land is cultivated can effectively change the carbon emissions by a factor of two.

And there are even more things to consider:

- Whether the crop has been grown in aerobic or anaerobic conditions. Anaerobic conditions - such as padi fields - cause the production of methane. World rice production may account for around a quarter of our global methane emissions, or 4-5% of the total climate impact of anthropogenic greenhouse gases.

- Whether the food involved cattle. Globally, cattle account for about 28% of global methane production - another 5% of the anthropogenic greenhouse gas total. It is strange to think that the carbon dioxide that you breathe out may also have been responsible for generating methane, which is a far more potent greenhouse gas.

- Whether your food is frozen or fresh. My freezer consumes just over 200kWh of electricity to freeze about 80 litres of food (you can never fit the full amount in) per year. My electricity is 100% renewable, but on average in the UK 430g of carbon dioxide is produced for every kWh of electricity. That’s an extra 100kg of CO2 per year for a family, not including factory and transport cooling emissions.

Then there is the cooking; the way the food is sold; the amount of processing that goes into the food; and whether machinery or human power is used to plant, cultivate and harvest it. As I showed not far back, this last point can make a huge difference.

We produce food, we eat food, we exhale carbon dioxide - but on the way, a hell of a lot more happens to determine what greenhouse gases actually went into that simple breath.

Ultimately, if we don’t want the carbon from our bodies to be important, then we have to minimise the energy required to produce our food.


Fewer People

There is one last thing I want to look at, which goes right back to the beginning of this article. If we stop breathing then we die. But, to put it crudely, who dies makes a huge difference to the Earth.

A billion people breathing, anywhere on Earth, produces 500 million tonnes of carbon dioxide. Those billion people, breathing a total of 6.3 trillion breaths a year, all lead different lives. As we have seen, the food that is the source of that carbon dioxide determines the actual impact of those breaths that keep those billion people alive.

But in life so much more happens while those people breathe in and out.

According to the US Department of Energy:

- A billion Indians would have produced 1.04 billion tonnes of carbon dioxide in 2004.

- A billion Chinese would have produced 3.62 billion tonnes of carbon dioxide in 2004.

- A billion Germans would have produced 10.46 billion tonnes of carbon dioxide in 2004.

- A billion Americans would have produced 20.18 billion tonnes of carbon dioxide in 2004.

If a billion people stopped breathing then not only would there would be 500 million tonnes less carbon dioxide produced per year, but if those people had been relentless producers of climate changing greenhouse gases, the Earth might itself be able to breathe a sigh of relief.


(This article was originally published at  http://earth-blog.bravejournal.com/entry/22233)