Correspondence/Rebuttal Cite This: Environ. Sci. Technol. XXXX, XXX, XXX-XXX
pubs.acs.org/est
Response to Comment on “Resource Footprints are Good Proxies of Environmental Damage″
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ecosystem damage. This confirms the importance of combining different resource indicators as proxy of environmental damage.
n a recent contribution to this journal we showed that resource footprints provide a good approximation of damage to human health and ecosystems.1 In his correspondence article, Heijungs2 provides three arguments as to why this may not be the case:
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STATISTICS Heijungs argued that statistics such as Variance Inflation Factors (VIFs), Akaike Information Criterion (AIC) and residual standard errors are not valid as the observations (products) in our data set are a nonrandom sample. Although we do agree that the ecoinvent database may not provide a random sample of all the products from the world’s economy, we consider the sample as representative as possible given that ecoinvent contains a large number of commodities from a wide range of product categories. From this large database we selected 976 products in such a way that as many products as possible were retained, while removing pseudo-duplicates. To demonstrate the robustness of our statistics to possible remaining non-independence/pseudo-replication in the product selection, we refitted the models 10 times based on a random subsample of 500 products. Each time this yielded the same set of predictors, as selected based on AIC values and VIFs, for both ecosystem and human health damage. Further, for both ecosystem and human health damage, the residual standard error varied from 0.22 to 0.26 in the random sampling procedure, whereas the residual standard errors we originally calculated from our full data set of 976 products were 0.24 and 0.25 for ecosystem and human health damage, respectively. This confirms the robustness of the statistics we presented. In conclusion, we consider the criticism from Heijungs as not justified. Our additional analyses, as presented above, provide further evidence that in the vast majority of product comparisons, resource footprints are indeed good proxies of environmental damage. Zoran J.N. Steinmann*,† Aafke M. Schipper†,∥ Mara Hauck†,⊥ Stefan Giljum‡ Gregor Wernet§ Mark A.J. Huijbregts† † Department of Environmental Science, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands ‡ Institute for Ecological Economics, Vienna University of Economics and Business (WU), Welthandelsplatz 1, 1020 Vienna, Austria § Ecoinvent, Technoparkstrasse 1, 8057 Zurich, Switzerland
1. Potential of rank reversal in product comparisons by using resource footprints instead of environmental damage. 2. Arbitrary choice of functional unit. 3. Incorrect statistics. We will argue below why the criticism of Heijungs is not justified.
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RANK REVERSAL Heijungs plotted the rank scores of the 976 products based on human damage footprints against the rank scores based on resource footprints and stated that “every point that is not on the diagonal line forms a possible rank reversal”.2 A possible rank reversal is, however, not the same as an actual rank reversal. To reveal how often rank reversals actually occur, we identified the total number of cases in which a comparison of any two products in our data set would lead to a different ranking based on the resource as compared to the damage footprints (i.e., product A better than product B according to the resource footprint proxy but worse according to the damage footprints or vice versa). We checked all 475 800 possible pairwise comparisons and found that resource- and damagebased ranks were identical in 90.6% and 92.4% of the cases for ecosystem and human health damage, respectively. Thus, actual rank reversals are relatively rare, indicating that results for resource footprints and damage footprints do indeed point in the same direction for the vast majority of products.
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FUNCTIONAL UNIT Heijungs used our initial data set to calculate damage per MJ of fossil energy rather than the common unit of 1 kg of product. He concluded that the remaining variance in environmental damage per MJ between the products is too large to consider resource footprints as sensible proxies. Heijungs missed the main point of our analysis here. In the past, energy as single proxy of damage was promoted by Huijbregts et al.3 and later criticized by Laurent et al.4 In the current analysis we dealt with this criticism by including not only fossil energy, but also land, water and materials as possible proxies of environmental damage. Following the same rescaling procedure as Heijungs, we refitted our model, without fossil energy demand as a predictor (i.e., we used damage per MJ of fossil energy as response variables and the other three resource footprints as predictors). The three remaining resource footprints indeed explained a significant part of the variation in environmental damage (per MJ of fossil energy), that is, 49.8% of the variation in human health damage and 73.8% of the variation in © XXXX American Chemical Society
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AUTHOR INFORMATION
Corresponding Author
*Phone: +31 24 365 2393; e-mail:
[email protected].
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DOI: 10.1021/acs.est.7b04926 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Correspondence/Rebuttal
ORCID
Zoran J.N. Steinmann: 0000-0001-8606-917X Present Addresses ∥
PBL Netherlands Environmental Assessment Agency, Bezuidenhoutseweg 30, 2594 AC, The Hague. ⊥ TNO, Princetonlaan 6, 3584 CB Utrecht, The Netherlands. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Steinmann, Z. J. N.; Schipper, A. M.; Hauck, M.; Giljum, S.; Wernet, G.; Huijbregts, M. A. J. Resource Footprints are Good Proxies of Environmental Damage. Environ. Sci. Technol. 2017, 51 (11), 6360− 6366. (2) Heijungs, R. Resource Footprints are Bad Proxies of Environmental Damage. Environ. Sci. Technol. 2017, DOI: 10.1021/ acs.est.7b04253. (3) Huijbregts, M. A. J.; Hellweg, S.; Frischknecht, R.; Hendriks, H. W.; Hungerbühler, K.; Hendriks, A. J. Cumulative energy demand as predictor for the environmental burden of commodity production. Environ. Sci. Technol. 2010, 44 (6), 2189−2196. (4) Laurent, A.; Olsen, S. I.; Hauschild, M. Z. Limitations of carbon footprint as indicator of environmental sustainability. Environ. Sci. Technol. 2012, 46 (7), 4100−4108.
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DOI: 10.1021/acs.est.7b04926 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
