More than one way to fall off a cliff

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Wonkometer Warning MH-225The “energy cliff” is a central concept in ecological economics, and it’s based on a very simple ratio. But for me this principle was a slippery thing to grasp, and I eventually realized some of the most common graphs used to illustrate the Energy Cliff were leaving me with a misleading mental image.

This column takes a closer look at Energy Return on Energy Invested (ERoEI, EROEI or simply EROI) and the Energy Cliff, concluding with the question of how and whether the Energy Cliff might be experienced as a historical phenomenon.

The Energy Cliff as a mathematical function

Below are two frequently used versions of the Energy Cliff graph, based on the pioneering work of Charles Hall. They illustrate the relationship between Energy Return on Energy Invested and the percentage of energy production that is “surplus”, i.e., not needed by the energy sector for its own work and therefore available for use by the rest of society.

Chart accessed via

Chart accessed via

Chart from Tim Morgan, Life After Growth, Kindle edition, locus 980

Chart from Tim Morgan, Life After Growth, Kindle edition, locus 980

In each case the EROEI is shown on the horizontal axis with lowest values at the right. The apparent suddenness of the drop-off in surplus energy depends on the relative scales of the axes and maximum value shown for EROEI, but in each case the drop-off becomes nearly perpendicular as EROEI falls below 10 – thus the name “Energy Cliff”.

Simple enough, eh? But after seeing this graph presented in several books and essays, I still found the concept hard to master. I kept asking myself, “How does that work again?” or “Why does energy supply drop off so suddenly?”

The problem, I realized, is that the impression these graphics leave in my mind is at odds with the intent. As these examples show, the “Energy for society” or “Profit energy” dominates the graphic visually, and the “Energy used to procure energy” or “Cost energy” seems like such a small sliver that it couldn’t possibly be that important. Mathematically naïve as that impression may have been, it nevertheless made it difficult for me to retain a clear understanding of the Energy Cliff.

The solution for me was to play with the graph until I felt I understood it clearly, using imagery that reinforced the understanding.

It was most helpful, I found, to present the graph not as an unbroken continuum between the two variables, but as a bar chart showing discrete values of Energy Return on Energy Invested: 1, 2, 3, 4, etc up to 50.

The Energy Cliff as a Bart Chart

Visualizing the numbers this way minimizes the tendency to see the surplus energy, or Net energy output, as one massive block. Just as importantly, it allowed me to easily focus on the relationship between specific values of Energy input and Net energy output.

For example, at the far right end of the graph is the ERoEI value 1. This corresponds to a bare break-even scenario. An oil well with this ERoEI would not be worth drilling: we would use up one barrel of oil to drill and operate the well, and it would spit out exactly one barrel in return, leaving us with no surplus energy for our efforts.

An ERoEI of 2 corresponds to a Net energy output of 50%. To return to our Proverbial Oil Corp., we burn one barrel of oil to drill and operate a well, and the well spits out two barrels, leaving us with a net gain of 1 barrel or 50% of the Total energy output.

Our oil wells with ERoEI of 3 give us 3 barrels total for every one we invest, for a net energy gain of 2 barrels or 66.6%, wells with ERoEI of 4 give us a net energy output equal to 75% of their total energy output, wells with ERoEI of 5 give us a net energy output equal to 80% of their total energy output, and so on.

We can also see clearly that the Energy input and Net energy output percentages change very slowly for ERoEI values above 20 – at which point Energy input is 5% and Net energy output is 95% of Total energy output).

There is another simple tweak to this chart that can vividly illustrate the sudden drop-off: animation. (And since most of us use supercomputers capable of guiding a moon mission for our morning reading, why not throw in some animation?)

The animated Energy Cliff – click chart to set in motion

The animated Energy Cliff – click chart to set in motion

By focusing attention on just a narrow range of ERoEI values at a time, this moving bar graph illustrates the fact that Net energy output changes slowly throughout most of the range, and then drops off suddenly and swiftly.

The animated graph relies on the element of time as a key facet of the presentation. That begs the question: can the Energy Cliff chart be read as a function of time?

The Energy Cliff as a historical phenomenon

It is easy to look at the Energy Cliff graphic as a chronological progression, given the convention of viewing timelines with past on the left and future on the right. That would be a mistake – there is no element of time in the chart – but it might be a useful mistake if made consciously.

It’s true that ERoEI rates have been declining slowly for the past 50 years, and many new energy technologies today have ERoEI rates of 10 or lower. And in fact, the Energy Cliff chart is sometimes presented as evidence that an impending energy crisis is mathematically inevitable. While that would be an unwarranted extrapolation from a graph of a simple exponential curve, it isn’t hard to cherry-pick data that graphs to a shape similar to the Energy Cliff.

Consider the following table of ERoEI rates over time.

Selected ERoEI rates over time

This table starts with EROEI rates before the industrial age, and finishes with rates that could plausibly represent the collapse of industrial society. When graphed these numbers show a drop-off much like the Energy Cliff, with the addition of a steep slope going up at the outset of industrial civilization. The values are roughly scaled chronologically, to represent the length of time during which very high EROEI prevailed – basically, the 20th century.

Net Energy over time - chart 1 copy


The numbers cherry-picked for this chart include, crucially, an EROEI for photovoltaic panels in Spain as calculated by Charles Hall and Pedro Prieto, which was the subject of spirited discussion recently on Resilience. At 2.45, this EROEI is far below the level needed to support a highly complex economy. If this number is correct and turns out to be representative of photovoltaics more generally, then the scenario suggested in the above chart is plausible. As high EROEI petroleum sources are depleted, we turn to bottom-of-the-barrel resources like tar sands, and then to solar panels which are even less energy-efficient. Complex industrial society soon collapses, and the vast majority of us must return to the fields.

For a very different picture, we could use the EROEI for solar panel installations presented by Ugo Bardi in Resilience, from a study by Bhandari et al. In this view, photovoltaics in Spain have an EROEI of 11–12, safely out of the drop-off zone of the Energy Cliff. In this scenario we’d have no need for last-ditch fossil fuels from tar sands, solar panels would produce enough surplus energy to create more solar panels and keep industrial society rolling cleanly along, and the Energy Cliff would be a mathematical function but not a historical reality.

Net Energy over time - chart 1 copy


These two charts are equally over-simplified, ignoring other renewable resource energy technologies with widely varying EROEI rates such as hydro-electric generation. It’s unknown how long we might stretch out the dwindling supply of high-EROEI fossil fuels, or whether there will be a collective decision to clamp down on carbon emissions and leave fossil fuels in the ground. And I’m unqualified to make any judgment on whether the Hall/Prieto or the Bhandari assessment of photovoltaics is most realistic.

In presenting these two different charts I merely want to illustrate that while the Energy Cliff graph of a mathematical function is simple and direct, extrapolating from this simple function to forecast historical trends is fraught with uncertainty.

Top graphic: “The Fool” in the Rider-Waite Tarot deck dances gayly at the edge of a precipice.


at the end of the day

As the sun sinks low the nighttime feeders are venturing out for breakfast, daytime feeders are grabbing a few more bites, and they can all be seen in the best light. Here are some recent photos from Bowmanville Marsh, in Port Darlington on Lake Ontario.

Naomi Klein, photograph by Joe Mabel, distributed via Wikimedia Commons

A renewable energy economy will create more jobs. Is that a good thing?

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In a tidal wave of good news stories, infographics and Facebook memes about renewable energy job creation, the implicit, unquestioned assumption is that More Jobs = A Healthier Economy.

A popular Facebook meme, based on the Stanford University Solutions Project, celebrates the claim that in a renewable energy-powered Canada, 40% more people will work in the energy sector.

From the Environment Hamilton Facebook page.

From the Environment Hamilton Facebook page.


In elaborate info-graphics, the Solutions Project provides comparable claims for all 50 US states and countries around the world – although “assertion-graphic” might be a better term, since the graphics are presented with no footnotes and no clear links to any data that might allow a skeptical mind to evaluate the conclusions.

From The Solutions Project website.

From The Solutions Project website.

And Naomi Klein, author of This Changes Everything and one of the proponents of The Leap Manifesto, cites the Energy Transition in Germany and notes that 400,000 new jobs have already been created. In her hour-long talk on the CBC Radio Ideas program and podcast, Klein gets at some of the key issues that will determine whether More Energy Jobs = A Good Thing, and we’ll return to this podcast later.

To start, though, let’s look at the issue through the following proposition:

The 20th century fossil-fueled economic growth spurt happened not because the energy industry created many jobs, but because it created very few jobs.

For most of human history, providing energy in the form of food calories was the major human occupation. Even in societies that consumed relatively high amounts of energy via firewood, harvesting and transporting that wood kept a lot of people busy.

But during the 19th and 20th centuries, as the available per capita energy supply in industrialized countries exploded, the proportion of the population employed supplying that energy dropped dramatically.

The result: instead of farming to provide the carbohydrates that feed humans and oxen, or cutting firewood to heat buildings, nearly the whole population has been free to do other activities. Whether we have made good use of this opportunity is debatable, but we’ve had plenty of energy, and nearly our entire labour force, available to run an elaborate manufacturing, consumption and service economy.

Seen from this perspective, the claim that renewable energy will create more jobs might set off alarms.

What’s in a job?

Part of the difficulty is that when we speak of a job, we refer to two (or more) very different things.

A job might mean simply something that has to be done. In this sense of the word, we don’t usually celebrate jobs. If we need to carry all our water in buckets from a well five kilometers from home, there are a lot of jobs in water-carrying – but we would probably welcome having taps right in our kitchens instead. Agriculture employs a lot of people if the only tools are sticks, but with better tools the same amount of food can be raised with fewer people working the fields.

So when we think of a job as the need to do something, we typically think that the fewer jobs the better.

When we celebrate job-creation, on the other hand, we typically mean something quite different –  a “job” is an activity that is accompanied by a pay-cheque. Since in our society most of us need to get pay-cheques for most of our lives, job-creation strikes us as a good thing to the extant that pay-cheques are involved.

Here’s the wrinkle with renewable energy job creation: the renewable energy transition will likely create jobs in the sense of adding to the quantity of work that must be done (which we normally try to minimize) and jobs in the sense of providing pay-cheques (which we typically want to maximize). The two types of job-creation are at cross-purposes, and the outcome is uncertain.

Allocation of energy surplus

Widespread prosperity depends not only on what work is done and what surplus is produced, but on how that surplus is allocated and distributed.

In the middle of the 20th century in North America and Europe, only a few people worked in energy supply but they produced a huge surplus. At the same time, the products of surplus energy were distributed in relatively equal fashion, compared to the rising levels of inequality today. The mass consumption economy – a brief anomaly in human history which is ironically referred to as Business As Usual – depended on both conditions being met. There had to be a large surplus of energy produced (or, more accurately, extracted) by a few people, and this surplus energy had to be widely distributed so that most people could participate in a consumer economy.

Naomi Klein gives prominent emphasis to the second of these two conditions. In her CBC Radio Ideas talk, she says

There’s a group in the US called Movement Generation which has a slogan that I quote a lot, which is that “transition is invevitable, but justice is not.” You can respond to climate change in a way that people putting up solar panels are paid terrible wages. In the US prison inmates are making some of the solar panels that they’re putting up. … There has to be a road map for responding to climate change in an intersectional way, which solves multiple problems at once.”

She cites the German Energy Transition as an encouraging example:

There are 900 new energy co-operatives that have sprung up in Germany. Two hundred towns and cities in Germany have taken their energy grids back from the private companies that took them over in the 1990s, and they call it “energy democracy”. They’re taking back control over their energy, so that the resources stay in the communities and they can use the profits generated from renewable energy to pay for services. They’ve also created 400,000 jobs as part of this transition. So they’re showing how you solve multiple problems at once. Lower emissions create good unionized jobs and generate the revenue we need to fight the logic of austerity at the local level.”

In Klein’s formulation, democratic control of the energy economy is a key to prosperity. Because of this energy democracy, the new jobs are “good unionized jobs” which “fight the logic of austerity”. But is that sustainable in the long run?

As Klein says, in Germany’s “energy democracy” they use “the profits generated from renewable energy to pay for services”. But that presupposes that the renewable energy technologies being used do indeed generate “profits”.

It remains an open question how much profit – how much surplus energy – will be generated from renewable energy development. If renewable energy developments consume nearly as much energy as they produce, then in the long run the energy sector may produce many pay-cheques but they won’t be generous pay-cheques, however egalitarian society might be.

Book cover, Life After Growth by Tim MorganEnergy sprawl

Tim Morgan uses the apt phrase “energy sprawl” to describe what happens as we switch to energy technologies with a lower Energy Return on Energy Invested (EROEI).

‘energy sprawl’ … has both physical and economic meanings. In physical terms, the infrastructure required to access energy and deliver it to where it is needed is going to expand exponentially. At the same time, the proportion of GDP absorbed by the energy infrastructure is going to increase as well, which means that the rest of the economy will shrink.” (Life After Growth, Harriman House, 2013, locus 2224)

As Morgan makes clear, energy sprawl is not at all unique to renewable energy transition – it applies equally to non-conventional, bottom-of-the-barrel fossil fuels such as fracked oil and gas, and bitumen extracted from Alberta’s tar sands. There will indeed be more jobs in a renewable resource economy, compared to the glory days of the fossil fuel economy, but there will also be more energy jobs if we cling to fossil fuels.

As energy sprawl proceeds, more of us will work in energy production and distribution, and fewer of us will be free to work at other pursuits. As Klein and the other authors of the Leap Manifesto argue, the higher number of energy jobs might be a net plus for society, if we use energy more wisely AND we allocate surplus more equitably.

But unless our energy technologies provide a good Energy Return On Energy Invested, there will be little surplus to distribute. In other words, there will be lots of new jobs, but few good pay-cheques.

Top photo: Canadian author and activist Naomi Klein, photographed by Joe Mabel in October 2015, accessed via Wikimedia Commons