Though energy consumption is a fair approximation of
overall environmental impact, the emissions of
substances that are toxic to humans don't correlate
very well to energy.2 Emissions of toxics tend to
correlate more closely to direct human health impacts,
rather than environmental impacts. MacLean and Lave
report the toxic releases related to car manufacture
and use, and these appear in Figure 2. Interestingly,
any environmental or health impacts related to toxic
releases will be split fairly evenly between manufacture
and use, in contrast to energy, which is dominated by
the use stage.
This LCA, as well as many others like it, clearly
indicate that the bulk of environmental impacts from
automobiles occur during the use stage. The implicit
message is that if you can replace your car with one
that is more energy efficient, chances are high that you
truly will be reducing your overall environmental impact.
However, if you are a person who considers toxic
releases more important than energy use, then it is
wiser to hold on to your existing car, in order to avoid
promoting the manufacture of a new one.
1 ILEA regularly prints reviews of LCA research published
elsewhere. These reviews often leave out many details of the
summarized work, and opinions expressed by ILEA may not
be the same as those of the original author(s). Please consult
the author's original work for a full treatment of their analysis
and perspective. The full citation for the work described here
Maclean, Heather L. & Lester B. Lave, "A Life-Cycle Model of an
Automobile." Environmental Policy Analysis v.3 n.7 (1988), pp.
2 This is not a conclusion of MacLean & Lave, but rather a rule of
thumb used at ILEA based on our experience with life-cycle
inventories. The main reason for the lack of correlation is that
very small quantities of toxics can have large impacts; an
isolated source in one particular sector or stage can strongly
influence the overall result.
This summary first printed in the ILEA Leaf, Summer 2002 issue.
Last Modified on Sept. 12, 2003.