How bad is it, really? Putting units on environmental impacts

(This post primarily focuses on Eline de Backer, Joris Aertsens, Sofie Vergucht, Walter Steurbaut, (2009) "Assessing the ecological soundness of organic and conventional agriculture by means of life cycle assessment (LCA): A case study of leek production", British Food Journal, Vol. 111 Iss: 10, pp.1028 - 1061)

I have a lot of thoughts on this paper, as it was the first one I really tried to tackle (and in retrospect, perhaps not the best choice to start with, given how much the authors cite one of the other papers on my list - Schau and Fet, 2008). But it allowed me to start wrapping my brain around a number of things, including the topic of this post, which is: 'how do you actually measure environmental impacts'?

This is actually the third 'step' of the paper (after their scope determination and initial data collection) but I think the ideas stand nicely on their own.

General approach - pick a scapegoat

The authors presented a fascinating suite of categories and accompanying models and units for measuring environmental impacts. Almost every single type of impact was represented in a similar way (though obviously with different models and units). For each type of impact, a single culprit element or chemical was chosen as the unit of measure, and then other big contributors to the same category were converted into equivalent units of that original chemical.

Example: Climate change = carbon dioxide

An example that I found reasonably accessible with what I already knew was their measurement of 'climate change potential'. The unit of measure for this was equivalent kilograms of emitted carbon dioxide - not too surprising, considering how often it seems to be the molecule we talk about when discussing climate change. So to get your total number, you start by calculating (based off the amount of diesel burned by your tractors for instance) the actual amount of C02 emitted. You then add in other important greenhouse gasses, like methane and nitrous oxide, by converting them into equivalent kg of C02. So if methane is 20 times worse of a greenhouse gas than C02, then your one kg of methane becomes 20 of CO2. (Equivalent kg CO2 from methane = 20 * kg of methane)

Example: Green gunk = phosphate

Other units were less familiar to me, but fun to figure out. For example, eutrophication. Quick aside for anyone who isn't quite sure what that is: eutrophication is a term used to talk about biomass in water - so when you see a bunch of green pond scum (which is actually algae) in water, eutrophication is pretty high, quite possibly due to a bunch of fertilizer runoff. Meanwhile, that green gunk may be choking out whatever else lived there before, in addition to dying, drifting to the bottom, and getting decomposed by bacteria that consume oxygen, leaving fish and other bottom dwellers unable to breathe. (want to know more about eutrophication? Wikipedia provides.)

In this case, the unit of measure is equivalent kg of phosphate - both a common fertilizer ingredient (for both organic and conventional farms - more about the interesting overlapping practices of conventional/organic later) and a compound known to stimulate the kind of growth associated with eutrophication - not surprisingly, it can make both wanted and unwanted things grow. So first you take your amount of phosphate in the fertilizer being applied. Then other compounds with similar fertilizing properties (nitrate, ammonia, etc.) are converted into equivalent phosphate and added to the original phosphate number, just as with the climate change gasses being converted into and added to the carbon dioxide.

Other units used

The other categories took a similar tack. I'm not going to go into each quite as deeply, but here they are in a more abridged form. (note - each one of these models comes from a cited paper, so there's a lot more going on that I'm glossing over!)

Ozone depletion (in the stratosphere, which is where ozone is supposed to live) is another familiar one - the reference unit there is equivalent kg of CFC-11 (yes, that's the old classic CFC freon, that was used as a refrigerant back in the bad old days).

Abiotic resources - which means 'resources that are not living', like soil and water - depletion was measured in equivalent kg of antimony, a toxic element used in a lot of flame retardants.

Both human and terrestrial (ecosystem) toxicity were measured in equivalent kg of 1.4-dichlorobenzene. I didn't recognize this one, but apparently it's likely a carcinogen and causes illness when consumed. This one also included some segregation by the different effects of chemical concentration in air, different types of water or soil, and so on, with different toxicity weights for each.

Photochemical oxidant formation was a new term for me too, but as near as I can tell it seems to be the formation of pollutants in the lower atmosphere, which can take the form of smog. Acetylene (C2H2) is an organic compound prone to reacting and forming these kinds of chemicals, including low atmosphere ozone (which is not good for people or plants)

Acidification, on the other hand, is more familiar. Sulfur dioxide is the big culprit and reference substance here, due to its unfortunate ability to mix with water in the atmosphere and create one of the most famous environmental problems - acid rain.

Now what?

Obviously each of these is something of a simplification, but they each provide a way to get a grip on a type of pollution known to cause real problems. With these defined, we can use them as points of comparison for environmental impact. More on that coming...