For some time, I’ve been vaguely aware of some ‘research’ that purported to show that a GM Hummer was more eco-friendly than a hybrid Toyota Prius over its entire lifecycle. This puzzled me greatly so I decided to have a look myself.

In March 2007, a market research company called CNWMR published a report called ‘Dust To Dust‘ which appeared to show that, taking into consideration energy over the whole lifecycle, the energy cost of a Prius was $3.25 per mile whereas the Hummer H3 was only $1.949 per mile (dig the precision). This caused jubilation amongst the reactionary press and blogosphere and outrage amongst their progressive counterparts.

While many of the latter produced long lists and reports of what was wrong with the CNWMR analysis, I personally believe there is one big fatal flaw.

CNWMR factored in the different driver behaviour of the two vehicles – an average of 100 000 miles across its lifetime for the Prius and 400 000 ish for the Hummer. The Prius does have a higher energy cost to build (partly due to the battery, partly because it is unique so cannot share facilities with other models), so this skews the analysis heavily against the Prius as the smaller build energy for the Hummer is spread more thinly against all those miles.

To put it in layman’s terms the argument is: the Prius is more damaging because its drivers drive less.

Or conversely: if you drive more then your vehicle is more eco-friendly!

Ludicrous!

This clearly demonstrates the WYGIWYN (what you get is what you need) effect associated with life cycle assessments. If LCA is to be used to make clear judgements between products then standardised methods are required (as with fuel efficiency or energy labelling) to ensure that this sort of idiocy is not given the oxygen of publicity that I’ve just given it!