From time to time, the Ecological Footprint enjoys spikes in media coverage stemming from our campaigns, scientific reports and our work with governments. Some of this media coverage occurs in response to criticism of the science underlying the Footprint accounting methodology, or of the validity of the results.
As a science-based organization, Global Footprint Network welcomes scientific debate, as it helps us maintain our scientific rigor, improve our methodology and ensure its transparency. We have even published our own criticisms of the methodology to help drive its continuing refinement and comprehensiveness. And when a published critique is based on a mistaken understanding of how the methodology works or the research question it is intended to address, it provides us with a welcome opportunity in the media to clarify just what the Footprint is, and why it is so useful.
In recent weeks, the online edition of New Scientist and blogs on the Scientific American and Nature Conservancy websites discussed Does the Shoe Fit? Real versus Imagined Ecological Footprints, an article critical of the Ecological Footprint published in the November 2013 issue of PLOS Biology. While the article’s authors acknowledge the value of ecological resource accounting, “the broad influence and popular appeal” of the Ecological Footprint and the role of Footprint data “continu[ing] to infuse policy discussions,” they also question the Ecological Footprint’s relevance, arguing that Footprint measurements are misleading.
Like earlier critics, the PLOS article authors argue that, at a global scale, the carbon component of the Ecological Footprint — 55 percent of humanity’s total Footprint — largely accounts for the extent to which humanity’s demand for ecosystem services overshoots the planet’s capacity to meet this demand, and thus should be measured independently of the other Footprint components. Others have made a similar argument — that the demand for carbon sequestration is fundamentally different from the demand for renewable resources like food, fiber and timber, and thus the carbon Footprint should be disaggregated from these other Footprint components.
But precisely because the planet’s productive area is limited, and land used to sequester carbon emissions cannot also be used to provide renewable resources such as crops, it is only the sum of the area required to meet all these demands than can reveal the extent to which we are or are not living within the ecological capacity of the planet. An aggregated accounting also provides a systems perspective that clearly reveals tradeoffs important to policymakers: If we want to use forests to sequester carbon, for example, these forests can’t also be used for wood and wood products, nor can they be cleared to grow crops.
As the Ecological Footprint has garnered widespread attention in the popular media, it is not surprising that the measure and its results have been described with varying degrees of accuracy. Often people read into the metric what isn’t there. Some have taken it to be all-encompassing, incorrectly believing that it incorporates measures of ecosystem degradation such as soil erosion or water depletion; others confuse it as synonymous with the simpler carbon footprint. Despite the extensive documentation of the accounting methodology that Global Footprint Network makes freely available, even some of those who have published criticism of the Footprint in scientific journals have misunderstood what the Footprint measures. As New Scientist’s Fred Pearce acknowledged in his opinion piece, the Ecological Footprint “does not measure the things that most of us assumed it does.”
So just what does the Footprint measure, and why is this so important in setting policy to move us toward a sustainable society? The strength of the Ecological Footprint lies in its ability to answer one critical research question: How much of the planet’s large but limited ecological capacity is used by humanity? This question can help determine not only how much capacity is available, but also the extent to which different demands—e.g., for housing, transportation, food, goods and services — are competing for this ecological capacity. The metric can be applied at any scale, from an individual’s lifestyle to the economy of a city or nation, to humanity’s demand on the planet as a whole. No indicator answers this research question better than the Ecological Footprint.
And it’s an essential question, because unless human demand “fits” within the capacity of the planet, sustainability will remain elusive. But while the Footprint is a measure of this “fit,” used alone the metric is not sufficient to tell us if we are sustainable. A more complete picture is provided by using the Footprint in conjunction with other indicators. For example, if sustainability is defined as “living well, within the means of the planet,” the Footprint can give an indication of the latter, and it is often paired with the UN’s Human Development Index (HDI), an index of well-being, to help complete the picture.
Pearce also questions the Footprint’s relevancy for policy makers, arguing that it tends to underestimate human demand on the planet. In calculating global overshoot, Ecological Footprint methodology — like that used by the Intergovernmental Panel on Climate Change (IPCC) — is by design conservative. It may underestimate human demand and overestimate the ecological capacity available to meet this demand; if so, this helps ensure that claims of overshoot can’t be dismissed as exaggerated. But scientists don’t ignore climate change because the IPCC conservatively underestimates the extent of carbon emissions, nor should we ignore what the Footprint tells us: Current demand on the planet is more than its ecosystems can keep up with, and continuing on this course will inevitably deplete resource stocks or allow the continuing accumulation of carbon in the atmosphere.
We look forward to working with others to continue improving Ecological Footprint accounting. Nations need to know how much of Earth’s ecological capacity humanity is using, and no indicator measures this better than the Ecological Footprint.
Check out our latest commentary on the value of Ecological Footprint accounting, How Much Nature Do We Have to Use?, published on Scientific American’s guest blog.
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