associated with ecological services or a land area. Because the biosphere cannot assimilate any of these materials within human timescales, integration of these factors into Footprint calculations would result in infinitely large, and therefore meaningless, values. n
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Ecological degradation. The Footprint does not directly measure ecological degradation, such as increased soil salinity from irrigation, that could affect future productivity. However, if degradation leads to reductions in biological productivity, this loss is captured in future biocapacity accounts. The Footprint is not predictive in this sense, but documents effects as they occur. This avoids making Footprint assessments speculative. Resilience of ecosystems. Ecosystems have the capacity to tolerate some disturbance without collapsing. Excessive disturbance, leading to collapse, does not mean extermination of life, but rather a shift of the ecosystem into a qualitatively different state, with a new species composition.9
Aspects of demand for which data are sparse. Most of the underlying data sets used to calculate national Footprints and biocapacities come from the United Nations, namely from the UN Food and Agriculture Organization (UN FAO). These data sets do not include assessments of the uncertainty or reliability of included data. Accordingly, Footprint results must be interpreted with the proviso that they assume the underlying data is correct. When there is doubt about data values, Footprint calculations generally exclude or use lower estimates for demand on nature, and use optimistic biocapacity accounts. This is done to avoid exaggerating ecological deficits. Results, therefore, most likely underestimate the extent of humanity’s ecological overshoot.
Potential errors in the implementation of the 2008 Edition
What the Footprint does not measure well n
consider wider issues, such as costs, nuclear waste, military proliferation, and operational risks. The 2008 Edition no longer includes nuclear energy at par with fossil fuel.10
Waste flows. For many waste flows, inadequate data sets exist for Footprint calculations. For example, SOx emissions from fossil fuel-based power plants contribute to the acidification of rainwater, which has detrimental effects on forests, fish and wildlife. However, at this time, globally comparable data on the relationship between SOx concentration and biocapacity are lacking. Acid rain does not yet enter into Footprint calculations, but may in the future if better data become available. Freshwater use. Freshwater use is only indirectly included in the Footprint due to lack of data that link freshwater use with loss in bioproductivity. Some local Footprint assessments have included freshwater use, but national assessments do not yet do so. Freshwater shortages that do result in declining bioproductivity are reflected in biocapacity measurements. Making Ecological Footprint assessments more relevant to freshwater issues is a research task.
As with any other scientific measurement tool, the results need to be evaluated in terms of reliability and validity. This becomes a more complex task with accounts that aggregate an extensive array of data. This is particularly true for data such as that from the UN FAO, which does not specify confidence limits. Considerable care is taken to minimize any data inaccuracies or calculation errors that might distort the Ecological Footprint accounts, including inviting national governments to collaboratively review the accuracy of the assessment for their country, and develop improvements in the method either specific to their country or that generalize for all countries.11 In addition, efforts are continually being made to improve the transparency of the National Footprint Accounts, allowing for more effective internal and external quality assurance. Overall, the accounts are designed to err on the side of over-reporting Biocapacity and under-reporting Ecological Footprints, making it less likely that any errors will significantly undermine the conservative bias of the accounts. Six potential sources of error have been identified:
Nuclear power. The challenges with nuclear power are poorly captured with the Ecological Footprint, and hence the Footprint is ill-suited to analyze the utility or risk of nuclear power. When analyzing nuclear power one needs to
9. For more on resilience of social and ecological systems, visit the Resilience Alliance at http://www. resalliance.org. Since the Ecological Footprint does not predict but document past outcomes, it does not say anything about future resilience of ecosystems. If though, there is an ecosystem collapse (and the productivity shift can be measured), this collapse will be tracked by Footprint accounts in terms of the decreasing biocapacity of that ecosystem. If production Footprints are large, or even exceed, local biocapacity, the likelihood of an ecosystem collapse gets higher. However, Footprint accounts cannot determine the timing or kind of collapse the ecosystem will undergo. Therefore, as Deutsch et al. (2000) correctly point out, “when trying to answer questions on how to manage ecosystems in a sustainable way, or how to best distribute the goods and services generated by ecosystems, there are other methods better suited for the task� (Deutsch 2000).
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Conceptual and methodological errors. These include: o
Systematic errors in assessing the overall demand on nature. Some demands, such as freshwater consumption, soil erosion and toxic release are excluded or incompletely covered in the calculations. This typically leads to underestimates of ecological deficit. One particular issue is that the demand on biocapacity resulting from emission of greenhouse gases other than carbon dioxide is not currently included in Ecological Footprint
10. For more detail on why nuclear energy is no longer included in Footprint accounts as a separate component, see Appendix A. 11. For more detail, see section on research collaboration in Appendix D.