Time and Life Cycle Metrics Carbon Measurement

May 10, 2009
Deep Carbon Footprinting (tm)

I believe that it is time to take product life-cycle carbon footprinting to the next level. Deep Carbon FootprintingTM would look beyond static carbon footprinting, and explicitly consider the dimension of time in every part of a product's life cycle -- production, transportation, use, and disposal.

It would also look at a broader range of biophysical phenomena (including some second-order effects) that could potentially impact a product's real carbon footprint. Deep carbon footprinting is needed to really understand the relative contributions of different stages in a product's life cycle, which is the first step in any attempt to reduce the product's footprint.

Here are a few examples of the types of analyses that would be included in deep carbon footprinting (I'll be offering numerical examples from selected industries/products in future posts):

Consider the wood in a building or in a piece of furniture. The biogenic carbon in that wood is stored in the product as long as the product is in service. When the product (or a part of it) is disposed and landfilled, the wood might decompose aerobically or anaerobically (releasing its biogenic carbon atoms back into the atmosphere as either CO2 or methane) over a short or a long period of time, during which there is continuing but diminishing carbon storage in addition to the GHG emissions.

A similar analysis can apply to a piece of cotton clothing, or any other product that sequesters and then releases biogenic carbon.

Concrete in buildings and infrastructure continually absorbs CO2 from the atmosphere through a process called carbonation. At end of its service life, the concrete might be demolished and then either re-used as concrete aggregate or landfilled. Demolition/crushing increases the available surface area and potentially speeds up the carbonation. If we are looking at a 100-year assessment period, then the concrete would have to be credited with a certain amount of carbon sequestration, starting at 0 and ramping up over time. The carbon credit is not all the CO2 that is ultimately absorbed by the concrete in the 100 years, but a smaller amount that actually reflects the timing of all the absorption.

On a related note, trees planted in a landscape project should not take credit for the total CO2 absorbed over the average growing period of 20 years or so. Any CO2 absorbed in the first year is a lot more valuable than any CO2 absorbed in the 20th year, so the time series of annual CO2 absorption amounts would have to be weighted appropriately based on the year of absorption and then summed together.

(Since the current carbon offset market doesn't consider the time dimension in this manner -- as far as I know -- offset purchasers may well be getting considerably less climate-change-mitigation than what they are paying for!)

Food waste is among the most easily decomposable materials in the waste stream. There is almost always some food waste before cooking and after cooking. Unless it is composted properly, most of the food waste will turn into methane under anaerobic decomposition over time (biogenic carbon released as CO2 very soon after production is climate neutral, but any biogenic carbon that is released as methane is decidedly not neutral unless it is recovered and used as fuel). Once again, the timing is important.

We've seen that this effect can sometimes exceed the transportation impact as far as carbon footprint is concerned.

We are currently incorporating a Deep Carbon FootprintingTM methodology into several new industry-specific carbon footprint tools that are in development. More on this in future posts.

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