The carbon footprint of your diet

30 Mar 2015

It is Cambridge Science Festival time again and so far I have been to five events, ranging from lectures to panel discussions to hands-on demonstrations. What has struck me is the enthusiasm and modesty of the very high calibre presenters and the open-mindedness of the audiences. 

For instance, in one panel discussion on sustainability, a contributor from a campaigning organisation criticised big business but some of the younger members of the audience argued that it was only through business that society will improve its record. It was done in the context of a genuine debate about the issues rather than the shouting matches that I regularly experience when such issues are ‘debated’.

I had a similar experience in a workshop on choosing food that is good for the planet through reducing the carbon footprint of personal diets. It was run by the charity Cambridge Carbon Footprint ( Within a few minutes a member of the audience said that to achieve this aim we should all eat organic food. I commented (with some trepidation) that the overwhelming evidence suggests that conventional food has a lower carbon footprint and then almost ducked to avoid a boisterous rebuttal. However, the audience remained calm and one of the two co-presenters said that her understanding was the same as mine. She added that there are issues regarding the carbon footprint of food consumption that perhaps conflict with some ideological agendas. As another example, she said that plastic shopping bags have a lower carbon footprint than paper shopping bags. This exchange suggested that it was going to be an ideologically free debate.  It turned out to be great.

The workshop tackled the issue of getting reliable data on which to base decisions. It is extremely difficult to estimate Greenhouse Gas (GHG) emissions and everyone present accepted that it is almost impossible to achieve accurate data. This is partly due to having to decide what is and what is not included in any calculation.

We were told that in the UK, the average annual GHG emissions per person is around 12 tonnes carbon dioxide equivalent (this take into account other greenhouse gas emissions, such as nitrous oxide). I could not find exactly the same figure in the literature, which generally says around 10 tonnes. The higher figure quoted at the workshop may also take into account the GHG associated with the production of the goods imported into the UK, including imported food.

We were also told that of this 12 tonnes, 2.9 tonnes were due to the production, processing, distribution and packaging of the food we eat. When this figure was broken down, 49% was due to production, 24% processing, 19% transport and 8% packaging. It is obvious that for each food purchased these proportions will vary hugely. In the debate it was highlighted that buying from a nearby supermarket may be more carbon efficient than driving to a farmers’ market and so it is difficult to establish absolute rules about where to shop.

It is also difficult to develop absolute rules on imported food because its long distance transport by boat may have a surprisingly low carbon footprint.

However, there was general agreement that buying in-season vegetables should typically result in a lower carbon footprint and that generally meat carries a high carbon cost. Sometimes meat can have a more moderate carbon footprint; for instance if it is from animals grazed on uplands where little additional feed inputs are used.

The really bad news is that cheese almost always has a high carbon footprint and so I will have to view my beloved Stilton in a new light.Stilton

In most of the discussion, I felt that I was a paragon of virtue despite my love of cheese. I grow a very high proportion of our vegetables in my second-hand unheated glasshouse and on my allotment (which I access on my wife’s bicycle). In addition, I now grow cover crops on the allotment which I hope will largely obviate the need to dig it. Can it get any better?

Well, perhaps not because then we touched on the subject of food waste. Again there is the issue of defining food waste as well as measuring it. It seems that some estimates include such items as potato peelings. In this case, the huge waste removing carrot fly damage to the parsnips I grow must, at least, slightly tarnish my halo. Perhaps I could reduce our carbon footprint further by using insecticides to control this pest.

More on the Cambridge Science Festival next time.


Picture: Stilton - High carbon footprint but delicious.