Energy Descent

The Science, Research and Technology Group has chosen the topic of Energy Descent to present to you because we believe it is an issue that is both highly relevant to what we do collectively about climate change, and an issue that is generally ignored. The basic concept is quite simple but the details are complex and highly technical.

I am not an expert in this area and am presenting this information as a lay person for lay people.

The purpose of this presentation is to get us all thinking and learning about energy descent and its implication for the work we are doing in the Climate Forum.

Hopefully, we can together refine and deepen our understanding of this critical topic, and intelligently apply it to our work together at the local level.

What is Energy Descent?

For those unfamiliar with the issue it involves the fact that the total amount of energy our civilization has available to do work is declining and will continue to decline over the coming decades.

The reality of energy descent is based on basic laws of science – not on economic predictions or political decisions. What is not clear is the precise timing of the descent. But there are reasons, political and economic, as well as science based, to suggest it is already happening and will accelerate sooner rather than later.

Energy Basics

Our entire complex modern industrial civilization developed over the last century has been possible because of the almost magical properties of fossil fuels. The most salient feature of fossil fuels for purposes of this discussion is their energy density; they have an amazing amount of energy packed into a relatively small mass.

Think of how far a petrol powered car can travel on just 1 litre of petrol. Now imagine the effort it would take you to push that car that distance. And due to the inefficiencies of the internal combustion engine, about 2/3 of the petrol’s energy is actually wasted!

And we obtained the benefits of these magic-like fuels at relatively little cost. That litre of petrol likely cost less than $2. Would you accept $2 to push a car that distance?

The main point of the above demonstration in not how cheap our energy is. Far more important is the amount of energy it took to produce that litre of cheap petrol. Appreciating this simple fact is key to understanding both our energy history and energy descent.

This fact is critical to keep in mind throughout this discussion: it takes energy to produce energy. Anyone who has chopped some wood to heat their home or cook knows this intuitively. We make the effort to chop wood because it produces more energy for us to use when combusted than we put into the chopping. The ratio of energy output to energy input is high enough to make it worth doing, so we do it.

This simple fact is also true for all the fossil fuels we produce. It takes energy input to get the energy output to actually use. What is really important is not necessarily the total amount of energy produced, but the ratio of energy produced relative to energy required to produce it. This ratio indicates the level of surplus, or net energy, available. The higher the ratio the more surplus available to use. It is this net or surplus energy that allows us to do work; it is what has allowed us to build a complex industrial society.

Think of it like a savings account; for every dollar saved (energy input) you get it back with interest (the combined energy output). The net gain is like the interest earned – the interest is analogous to the net energy available.

Our Energy History

A bit of history is in order.

For simplicity, this discussion will focus on oil, but a similar story, albeit a more complicated one, could be told for coal and natural gas as well.

At the beginning of the last century the energy return on energy invested, or net energy, from conventional oil wells was about 100:1. Imagine that return for your savings! Yes, a net energy return of 100:1 is like getting $100 for every dollar deposited in your savings account.

All fossil fuels had extremely high net energy ratios compared to what civilization used before their widespread use. These pre-fossil fuel energy sources were largely wood, and human and animal power, as well as a little wind and hydro. The increase in energy available was approximately 300 to 400% with the advent of fossil fuels – an enormous boost to available energy and economic activity.

The advent of fossil fuel use transformed human societies. We used them to literally move mountains, fell forests, cover vast areas (often of previously good farm land) with concrete and steel, and travel into space. Fossil fuels have given us Disney land and the internet – all in just a few decades. Our entire modern industrial civilization has been built with the energy surplus or net energy from fossil fuel extraction. Just maintaining the existing infrastructure of a complex society requires vast amounts of energy; expanding it requires even more.

Our reliance on fossil fuels to power our economy over the last century has led us all to expect plenty of cheap energy. All our future planning is based on continued supplies of cheap energy. This expectation of a continuous supply of cheap, abundant energy to both maintain our industrial civilization infrastructure, and to continue growing our economy, is something we have all grown up with and generally take for granted. Governments and businesses, as well as households assume it will continue. Most environmentalists also make this assumption.

Of course, we know fossil fuels are finite resources and at some point will no longer be available. But we are generally not aware that fossil fuels will lose their lustre because of a decline in net energy, long before the resources themselves are physically exhausted.

Whenever anyone mentions an energy system to you, think first about its net energy return. Energy descent is about an inevitable decline in net energy.

Declining Net Energy

The 100:1 net energy return from the beginning of the last century is no longer available from oil. The high net energy returns came from conventional oil wells that have lots of natural gas mixed with the oil. This gas essentially pushes the oil out of the ground when a hole is drilled in the right place.

Globally, these conventional wells reached their peak of production around 2005. Peak production is the point where the greatest volume of oil can be extracted. After this point, both the level of production and net energy return decline. What happens after this inflection point is that lower volumes of oil can be extracted (because the gas generally is exhausted before the oil) even with higher energy inputs. Oil producers have to pump gas or even water into these wells to push the oil out. It takes a lot of energy to do this pumping. The result is a lower net energy return.

That is what happens with conventional oil wells. This led oil producers to extract oil from a wider variety of unconventional sources – arctic, deep sea, tar sands, fracking, shale, etc. Each of these unconventional sources require considerably more energy inputs to extract the oil, hence the net energy return is reduced. This reduction in net energy return from oil (and other fossil fuels because we always go for the easy stuff first) will have profound implications for how our societies work in the future.


This decline in energy available to do work is caused by several factors.

First of all, what remains of conventional oil (and there is still lots in the ground) is being produced at lower volumes and with a lower net energy return.

And all of the unconventional sources of oil have considerably lower net energy returns than the conventional oil they are replacing in the market. Tar sands extraction, for example, has a net energy return of only about 3:1. Oil on the market today is a mixture of conventional and unconventional sources and the resulting net energy is less than 20:1, and declining. As conventional oil is less and less available the net energy of the remaining mixture of fossil sources will decline dramatically.

Some scholars suggest that a modern industrialized civilization is unlikely to function with a net energy return of less than 10:1. My understanding is that we will be at that point within a decade or two. This is based on the facts that all the unconventional sources of oil have such a low net energy, and these unconventional sources are increasingly displacing what remains of conventional oil. And of course, fossil fuels are non-renewable, and discoveries of new oil deposits are smaller than in previous decades.

Won’t Renewables Save Us?

OK, so what about renewables – wind, solar, geothermal, tidal, etc? We need to move to renewables anyway because of the climate impacts of fossil fuels.

Yes, but.

The “yes” is that we need to stop burning fossil fuels to avert climate disaster, and as soon as possible. Renewable energy sources are an obvious advantage in many respects.

The “but” is that while renewables can provide cleaner energy than fossil fuels from a climate perspective, all renewable energy sources have a considerably lower net energy returns than fossil fuels. Remember, it is the net or surplus energy that allows society to function. Operating with a lower net energy has profound implications for our future.

And the production of renewable energy systems is not without their own, albeit different, environmental challenges. But let us focus on the net energy aspect to understand the concept of energy descent and its implications for a sustainable future.

Specific renewable technologies have different net energy ratios. Large scale wind is likely the highest net energy return at about 18:1. Solar is generally lower, around 10:1.

The intermittency and storage issues associated with renewables are being addressed in a variety of ways, from smart grids over multiple time zones, to pumping water or lifting weights to store energy for later use. Redundancy of infrastructure is another tactic to keep the energy flowing when the sun doesn’t shine or the wind doesn’t blow.

In order to understand the net energy implications of an extensive renewable energy system to replace fossil fuels, all of these technologies need to be considered.

A recent simulation of a Green New Deal type transition to 100%renewables concluded that accounting for all the redundancies required to deal with intermittency and the need for storage, the net energy at point of actual use is only 3: 1 [1].

Note that this ratio is well below the 10:1 net energy ratio scholars have suggested is required for a modern industrial civilization to function.

Exactly how soon we will reach a net energy return from fossil fuels of 10:1 is uncertain as it involves demand as well as supply issues; but it is not far off with BAU.

But even if we have a 100% renewable system in place when that happens, the net energy available to actually do work may be much lower than we have become conditioned to expect. This is the basic concept of energy descent. And with a growing population energy descent is about both the absolute and per capita amounts of useable energy available; both will decrease.

The Energy Cliff

Declining net energy has some interesting characteristics. As net energy declines more and more of the total energy in a society is devoted to simply gathering energy – and less surplus is available to do other things. Initially the decline in net energy relative to total energy is gradual. However, at some level of decline, the decline accelerates rapidly. This is known as the energy cliff [2].

An energy analyst, Kurt Cobb, writes:

“And, this brings us to the idea of the net energy cliff. If our energy transition away from fossil fuels does not result in their replacement by high EROI sources of energy with the necessary versatility and storage characteristics, or if such replacements are possible, but delayed too long, then we may be facing a net energy cliff.

The net energy cliff graph

It may seem that the difference between an EROI of 40 to 1 and one of, say, 30 to 1 would be comparable to a move from 20 to 1 to 10 to 1. But the mathematics say otherwise. In a society that has an EROI of 40 (which is approximately what the United States is thought to have) about 2.5 percent of the economy is devoted to gathering energy for the other 97.5 percent. If an economy has an EROI of 30 to 1, then the portion of the economy involved in gathering energy rises to about 3.3 percent. This is a significant jump, but probably manageable. However, an EROI that drops from 20 to 1 to 10 to 1 results in the doubling of the part of the economy devoted to securing energy from 5 percent to 10 percent. A further drop to an EROI of 5 to 1, puts 20 percent of the economy within the general classification of energy gathering. This is the net energy cliff”.

What this graph tells us is that with the current decline in fossil fuel net energy, and the lower net energy of an entire renewable system, our civilization is approaching the net energy cliff. Global oil net energy is currently less than 20:1, approaching the shallow part of the graph. The decline will accelerate more as we approach a net energy return of 10:1. Unfortunately, this energy cliff is largely invisible to governments, businesses and environmentalists; it will come with little warning.

Why Be Concerned About Energy Descent?

Energy descent deserves our serious attention because energy is needed for everything we do. If less energy is available then we will be forced to do less [3]. And if we have to do less then we will need to prioritize what we do – as well as what we stop doing. The social and political implications are enormous for a society dedicated to prosperity for all with continuous economic growth. A clash of ingrained expectations (continuous growth) and physical limitations (declining energy available) is inevitable.

There is clearly much to consider about the implications of energy descent. But the purpose of this discussion is simply to raise the issue in a way that we can first understand what it is. This understanding is important if we wish the basic science behind energy descent is to intelligently inform our planning to deal with climate change and its myriad implications.



  1. Our modern industrial civilization has been built with an almost magical energy source – fossil fuels – they are almost magical because of their high energy density
  2. Fossil fuels have been very easy to extract relative to the amount of energy they produce. They provide a huge surplus or net energy (much more energy is extracted than is used to extract them). It is this surplus energy that allows us to do things, to prosper as a society.
  3. The amount of surplus energy available from fossil fuels is declining because it now require more energy to extract the same amount – so we have less surplus or net energy available to do things
  4. The decline in surplus energy available is referred to as energy descent.
  5. Energy descent is accelerating and the descent is expected to accelerate even more rapidly soon
  6. Renewable sources of energy provide less surplus energy than fossil fuels. So even if we convert to 100% renewables we are very likely to have less energy available in the near future
  7. This energy descent is a physical phenomenon and cannot be reversed
  8. There are many ways to deal with energy descent but the first step is to understand it

It is important to understand energy descent so we can plan for a genuinely sustainable future.


[1] - Note that this study is a simulation and not necessarily definitive. More studies are needed. But it is the best information which seems to be available at this point.

[2] - Note in the quote below EROI stands for energy return on (energy) invested, and is the same as net energy.

[3] - This assumes that declines in energy will be greater than gains made by increased efficiencies – a reasonable assumption at this point. This assumption is challenged by notions such as the internet of things, but the large increases in efficiencies predicted are yet to be demonstrated.