On the complexity of things

I was quietly perusing the pages of a recent edition of New Scientist one recent Summer evening when the concluding sentence of an article caught my eye:

“ Producing a kilogram of cheese emits around 24 Kg of carbon dioxide or equivalents, compared with 100Kg for beef but well under 2Kg for most plant based foods.”

The 24kg figure was highlighted in red in the middle of the article, with the byline “How much carbon dioxide is emitted making a kilogram of normal cheese.”

The body of the article concerned some research at the Technical University of Denmark, about the production of casein, the main protein required for cheese production, from microbes. Apparently casein has been produced from bacteria for some time but it has been the phosphorylation, the addition of certain phosphate groups, which has proved problematic and the article reported some significant progress on this front [1].

New Scientist is a credible, popular science journal; each edition contains articles about innovative science. But I was angered by these throw-away comparative comments. Arriving at valid comparisons is a complex process which could have been summarised with an additional sentence or two. Am I right to expect a journal of this quality to offer something a little more valid? What would it have taken to provide a more accurate comparison? There are several threads here that require investigation.

I will ignore the carbon dioxide equivalent in this diatribe. That argument has been waging for years and many parties now accept that comparing the global warming potential (GWP) of a gas like methane, which is undoubtedly the major greenhouse gas emitted by dairy cows, to carbon dioxide is flawed.(See link to previous article ‘Methane its all sorted’ if you want to read more about this.)  Lets look a little more closely at comparing cheese, beef and “most plant based foods”.

Comparing ‘apples with apples’ is fundamental here, and beef, the meat derived from the bovine species, is produced under a wide range of farming systems. These will vary from extensive pasture grazing, where the cattle link intimately with the plant and soil ecosystem, to intensive feedlots, where cattle are grown using manufactured diets often including ingredients such as soya, imported from distant locations. We have written in a lot more detail on beef’s carbon footprint in previous series which you can read here [2]. Clearly, every kilogram of beef cannot carry the same standard 100Kg footprint and even if that was possible, the comparison would be limited by the differing nutritional values of bacterial manufactured casein and beef.

The same argument can be applied to cheese production which will also be the result of highly varied dairy systems; one cow producing a few litres of milk a day in a third world environment cannot be compared to the many thousands of litres of milk produced by each cow annually in an intensive dairying system. And the cheese manufacture itself will differ. A few kilograms of an artisan fromage can hardly be compared to many tonnes of mass manufactured cheese originating in stainless steel vats.

And as for “most plant based products” many of these will have by-products inedible to humans, some involve the distribution and use of agrichemicals and some, like paddy field rice, come with significant methane emissions. 

Making meaningful comparisons is complex. Even detailed life cycle analysis to establish in depth carbon footprints cannot account for the differing nutritional content of the products being compared. And while I am no Luddite and welcome innovative scientific solutions to carbon emission problems, a promising test tube experiment is many, many tonnes of carbon away from a production system which is producing a low carbon bacterial cheese substitute.

Pedantry? Perhaps! I would have accepted a concluding sentence stating that: "Comparisons with other food products are complex but this innovative method shows some promise of reducing the carbon footprint of a new type of cheese.” But when you start quoting numbers in a scientific magazine I, for one, expect them to be accurate.