environment sustainability

Are we really using 1.5 earths?

Human civilization is currently in overshoot, and uses the renewable resources of 1.5 earths every year. That’s an often-repeated claim in environmental circles, including on this blog. It’s a slightly tricky statement. If you don’t understand what biocapacity and overshoot are, it sounds impossible – like the athletes who ‘give 110%’.

Overshoot occurs when resources are consumed faster than they can be renewed, and when waste is created faster than it can be absorbed. You can consume more than the earth can provide in a year, but in doing so you deplete natural capital and next year the earth will be able to produce less. It’s not particularly complicated, but it’s not exactly intuitive either.

However, a new paper rejects the whole idea. It goes so far as to say that “ecological footprint measurements, as currently constructed and presented, are so misleading as to preclude their use in any serious science or policy context.” If this was from an American right wing think-tank, we’d know where to file it. But it’s not. It’s from the Breakthrough Institute and published in the PLOS Biology journal. So what’s the argument?

NZ footprint

The ecological footprint is made up of six components – fishing grounds, built-up land, crop, grazing and forest land, and an area of land to absorb our carbon emissions. The Breakthrough Institute authors point out that of those six categories, only carbon is in overshoot. The other five are in balance or in surplus.

Since the other categories aren’t in overshoot, the whole of humanity’s overshoot is essentially carbon. “If one excludes carbon, global biocapacity exceeds the footprint of consumption by about 45%.” So, says the paper, why don’t we drop talk of ecological footprints and just talk about carbon emissions? The central conclusion is that environmentalists should go “back to the drawing board” and come up with some new metrics that make “both ecological and common sense.”

The problem with this is that it is stating the obvious to say that land use doesn’t show a deficit. How could it? You can’t farm more land than there is on the earth. Consumption can only ever be equivalent to or below biocapacity. The only one of the six categories that can show a deficit is carbon.

The other categories still matter, because it is our total land use that determines whether or not we are in overshoot. If we didn’t use so much land for grazing and crops, there would be more forest to absorb our carbon.

The Breakthrough Institute also argue that summarising sustainability into a single headline figure may be a fool’s errand. “A set of indicators, each pertaining to an identifiable and quantifiable form of natural capital or ecosystem service, is likely to be more comprehensible and useful than a single aggregate index.” That’s true, in the same way that GDP is a very blunt instrument in measuring economic progress. But that doesn’t mean we should ditch ecological footprinting, or GDP for that matter – only that we should not privilege one metric above all others. It would certainly be rather rash to abandon footprinting techniques without any obvious alternative. It’s probably the most useful shorthand measure of sustainability at our disposal, however limited it may be.

So I’m not sure the Breakthrough Institute’s main criticism is valid, and I think they overstate their case considerably in suggesting that ecological footprinting has no place in science or policy. But the paper does highlight an ongoing problem in sustainability circles – our metrics are still confusing and over-complicated.

One of my enduring frustrations in writing about sustainability is the convoluted nature of its terms. ‘Carbon footprint’ is a complete mess of a metaphor – how can you have a footprint of gas? I imagine most people think of footprints as a trail left behind us rather than our shoe size. Expressing quantities of gas in tonnes is counter-intuitive too, and in acres of land even more so.  Then you get carbon, CO2 and CO2e to content with, which are often used inter-changeably but are not the same. It’s hardly surprising that many people aren’t entirely sure what’s going on, and that the unconvinced remain so.

I intend to carry on using the concept of ecological footprints for the time being, but I share the Breakthrough Institute’s hopes that somebody, somewhere, is working on something clearer and simpler.


  1. > ‘Carbon footprint’ is a complete mess of a metaphor – how can you have a footprint of gas?

    I agree. The idea of a “footprint” fits the Ecological Footprint which renders everything into area (gha, hectares) but it doesn’t suit carbon. They should stick to tonnes for that.

    1. Thanks for the link. They say it all. I think it really is not so difficult to understand that the overshoot percentage relates to continuously replenishable biocapacity.

  2. The first aspect that comes to mind is the very definition of “ecological footprint” which includes the permanent sustainability of our lifestyle . The critique aims at a simplified concept that is not normally used. To return to the quite fitting athletes example: 110% performance refers to a momentary burst output that comes at the price of massive follow-up exhaustion and, if becoming regular, severe healthy problems and eventually premature death. 150% ecological footprint of course does not mean we are using 150% of actual capacity – not even a high-school geography student would make that simple a mistake (i.e. when there is a single fish left, eating it would mean to use no more than 100%). The overshoot refers to the maximum SUSTAINABLE capacity, i.e. everything over 100% actually DEGRADES the resources.

    Concepts like ecological footprint or “ökologischer Rucksack” (ecological backpack) are very rough metaphors that only vaguely include systemic aspects and interconnections, but they nonetheless are very valuable, because simplifications ARE needed to have a common ground for discussions. The overshoot is very real, and the Footprint is a useful fact-based metaphor to illustrate it.

  3. Hi,

    I’m not saying that the eco brigade are missing the point, but I do think that they are missing ‘a’ point with the footprint argument.

    In my opinion it depends on what a statement like ‘We are using 1.5 earths’ is used for, it gets bandied about like a weapon, you’ll hear things like ‘You have to cut down on air travel – we are using 1.5 earths’ (or words to that effect). The problem is of course that the argument doesn’t make sense and so loses it’s ability to convince anybody. I also suspect that when someone who isn’t convinced that there is a problem is given an incorrect argument it is easy for them to reject the argument and at the same time reject the whole movement. So people will think ‘It’s impossible to be using 1.5 times the available space so therefore we are not using 1.5 earths and that probably means that the whole carbon thing is wrong to’.

    We need to come up with metrics that are actually correct, easy to understand and are easily explainable and relevant to people. For example ‘At the current rate of oil use in the UK, in ten years energy costs will be 35% of a typical families expenses’ (made up numbers). We should have a range of different metrics that will impact directly on peoples lives instead of the vague things we have now. Another example could be ‘Fuel cost to drive a mile’, for me currently about 12.3p/mile, 10 years ago it 7.6p/mile (approx), in 10 years maybe 37p/mile (made up number again), the point is that the number will be something that is going to affect the majority of people unless we do something about the situation.

    Good Luck

    1. @ Jim et al:

      I personally would prefer to make every citizen of earth get a science degree and read the related scientific papers. This is not exactly the case, so we NEED valid simplified arguments rooted in reality to communicate highly complex issues to non-experts. When you sit in a boat with a hole and the capacity of the bilge pump is lower than the flow rate of the water entering through the hole, you will sink. Is that argument a weapon? You have to start working and bail the water out with hats and buckets if you want to survive. Any exchange of monetary arguments between the passengers of the boat will not really have much of an impact on the holes flow rate. Obviously in our real world discussions about pricing is important, but the monetization of absolutely everything is part of the problem, and not a fundamental part of the solution. We have to move away from the misconception that “cost-benefit” always refers to money, have to understand that there are situations where no amount of money, no fiscal tool, no financial derivative of whatever complexity and no monetary indicator can aptly describe – let alone fix – reality. Usually I use the example of costs vs energy harvested related to bore holes. Looking at a single bore hole, it becomes ever more difficult and hence expensive to extract oil from it, the closer one moves to depletion of that given oil field. As long as the oil price rises and perhaps extraction technology gets cheaper the well may remain profitable despite rising extraction costs. It can even remain ECONOMICALLY profitable when finally the energy invested into the oil extraction exceeds the energy contained in the extracted oil volume. Quite obviously, however that is a physical impossibility for all fossil energy resources on a global scale. It means that on a local scale it may look as if money can solve the energy issue, but on the macro scale it can’t. The indicators therefore have to be rooted in physical reality and not in the basically imaginary monetary world. Energy balances, biological productivity, output per area, availability of fertilizer etc. etc. etc. Reality that is.

      Away from that, I have yet to see economic models that are able to predict pricing over periods of a decade or more. If you know one, kindly let me know, so I won’t have to worry about money in the future anymore :-).

      Cheers from Westphalia

      1. Great point Stefan. I am personally against this new drive to monetize “ecological services” most of the time. I can understand the intentions: to put some of these relationships in terms that more people can readily relate to, but trying to put a price on the biosphere is asking the wrong question. It’s translating concepts into a language that might be inherently counterproductive.

        To me it’s like trying to put a price on democracy. I’m sure someone could put together an economic model for why a dictatorship could be more economically successful than a democracy, but democracy isn’t for sale at any price. The same is true for the biosphere. It doesn’t matter what price points are pegged to what nature provides us, the number is still wrong. The environment isn’t valuable, it’s invaluable.

        Hopefully we can guide the conversation in the right direction rather than fostering the understanding that everything is for sale.

        1. Another simple example: is it possible to express the electrical and mechanical inner workings of a complex machine in terms of money? I.e. can we (re) engineer the machine if we understand every detail of its financial impact and meaning on the market? The answer is obvious. I often heard the argument when a species becomes extinct: what do we need it for? What did it do for us?.

          At the same time I really do not blame folks too much for mainly thinking in monetary terms. It is the ruling paradigm, deeply entrenched in that non-existing thing called “globalized culture”, and many younger adults already grew up with it in the same way as many medieval people grew up believing in witches and demons (quite a few still do). We need to re-establish the simple fact that money is a tool, and not an end in itself – much less should it be the core of a belief system, for if you poke it with a needle, it bursts. There is nothing inside of it. – except for, perhaps, hot air, or rather foul smelling H2S…

  4. Link exchange is nothing else however it is only placing the other person’s blog link
    on your page at suitable place and other person will also do same in support of you.

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