**The 3 Pillars of the Deep Decarbonization of Energy Systems**

Welcome to chapter three of lecture five. I kept you waiting and I’m really sorry for that, but now is the time to start to looking at the solutions to the challenge of the deep decarbonization of our energy systems. How can we do it, that is the question? And in particular, how can we do it while making sure that we satisfy the conditions for continued economic growth and development and making sure that there is growing prosperity over the globe. This is precisely what we’re going to discuss in this chapter.

But first let me recap what is the scale of the challenge. As we discussed previously, CO2 energy related emissions are of approximately *32 gigaton today*, gigaton or billion tons. To have a likely chance which let me remind you, we defined as a probability higher than two-thirds, higher than 66%, to have a likely chance then of staying within the 2-degree limit, the need to *get down to approximately 11 gigaton by 2050*.

By comparison, to have a 50% chance only, so only one of out two of keeping below the 2-degree limit, the need to reach approximately 15 gigaton by 2050. *So we’re roughly talking of a division by a factor two or even three of CO2 energy emissions in the next 40 years*.

When in the meantime the world *population* is expected to grow and it is expected to grow by approximately one-third by 2050 compared to today.

And the *world GDP* is also expected to grow and much faster in fact than the world population. It is expected to be multiplied by something like three by 2050 compared to today. So if we combine these different numbers together it means that we’re talking of *dividing emissions per capita* by something in between two-thirds and three-fourths by mid-century. And *dividing emissions per GDP* by a factor of six or nine by 2050, which is huge.

**And so how can we achieve this decoupling between population and GDP growth on the one hand and energy consumption and CO2 emissions on the other hand**?

If you’ve looked at the number, this is by any standard a major challenge, but this is certainly feasible. And I want to show you how.

The easiest way to understand how that can be done is to decompose the drivers of CO2 emissions. CO2 emissions can be expressed as the product of four inputs. *CO2 emissions equal population, that is the first term multiplied by GDP per capita, that is the second term, multiplied by energy use per unit of GDP, that is the third term, multiplied by the CO2 emissions per unit of energy, that is the fourth term*. If you multiply these four terms, you get simply the CO2 emissions.

I’m just decomposing CO2 emissions into these four terms to explain you where the emissions come from and in turn, to explain you how the emissions can be reduced, through which mechanisms in particular.

If we take as a given the *population trajectory* and if we assume a *rising trajectory of GDP per capita*, in line with successful economic growth and, and development, then the *CO2 emissions are driven mainly by the two last factors out of the four*.

The first is the energy divided by GDP. And the second are the CO2 emissions divided by energy.

The first term is what we call ** the energy intensity**, meaning very simply the amount of energy per unit of final output. The amount of energy we consume per unit of GDP we produce. The second term is the

**of energy, meaning the, the amount of carbon emissions per unit of energy we consume.**

*carbon intensity**So let’s look at the ways in which we can reduce these two different ratios?*

So first, the *energy intensity of GDP* or as I said very simply, the energy consumption divided by GDP. It can be reduced through what we call *energy efficiency and energy conservation* measures in all the energy end use sectors. And we’re going to look in detail at each of them. First, *passenger transportation and freight transport*. Second*, residential and commercial* buildings. And third*, industry.*

So what’s the difference in between energy efficiency and energy conservation?

Because I just used both. Well usually we call

*energy efficiency**the technical improvements of products and processes.*And we use the term,*energy conservation**to describe a broader set of measures, including not only technical improvements, but more profoundly structural and behavioral changes that lead to lower levels of energy consumed per unit of GDP*.

So let’s simply look at some examples to be very concrete and very precise. Examples of energy efficiency and energy conservation measures in *the passenger transport and freight transport*, for example to start with.

- Well first, improved vehicle technologies. That is more efficient vehicles. Vehicles using less gasoline for example per kilometer traveled.
- Second, what we can call smart urban design. You can think at least of two things. One, building public transportation systems to reduce the need for the use of private cars, but you can think even more profoundly about building cities in a way that minimizes the distance to travel from where we live to where we work. Again, reducing the need for private transportation cars.
- Third example. Optimized value change. Again, to minimize the distance, but this time the distance we need to ship the products from where they are produced to where they are consumed.

If we look at *the residential and the commercial building* sector, we can also think of a number of different options.

- First, improved end use equipment. So more energy efficient equipment in our buildings.
- But also what we could call smart architectural design. So building our houses in a way that reduces the need for cooling or heating for example.
- More generally, improved building practices to improve the energy efficiency of the building envelope and also the use of different, less energy intensive construction materials.

If we look at the *industry sector*, again, many different options for an energy efficiency such

- as improved equipment and production processes,
- material efficiency, but also very importantly because the industry is a huge consumer of heat to produce its products.
- So reuse of waste heat is an important part of the energy efficiency measures in industry.

So that’s it for all the different ways in he different sectors in which we can improve the energy efficiency of GDP.

So the ratio of energy consumption divided by GDP. But as I said, it’s not the only driver of possible emission reductions.

We now need to looked at the other term, the improvement in the carbon intensity of energy or *the ratio of CO2 emissions per unit of energy* consumed. And here too the carbon intensity of energy can be reduced in two different ways.

The first is and very importantly, because it’s really at the core of any successful deep **decarbonization strategy**, it is the *decarbonization of electricity generation*. So as I said, your objective is the replacement of the uncontrolled fossil fuels, the phase out of the uncontrolled fossil fuels to produce electricity by a mix of different options, because there are different options to produce electricity with no or very little CO2 emissions.

The first is a *mix of all different sorts* of renewable energy such as hydropower, wind power, solar power, or geothermal energy. But you can also think of using nuclear power or using the fossil fuels, so the coal and the gas used to produce electricity, but with carbon capture and sequestration. So that’s a first important way in which we can decrease the carbon intensity of energy, by decarbonizing the way we produce electricity.

There is another way which we call *fuel switching*. It means switching end use energy supplies from highly carbon intensive fossil fuels in transportation or in buildings and in the industry to lower carbon fuels. Electricity is of course one of these possible lower carbon fuels, provided it is decarbonized. But there are other possible forms of lower carbon fuels and in particular, the use of biofuels. So again, this is another way of reducing the carbon intensity of energy which we call fuel switching, switching fuel from high carbon to low carbon sources of energy. So let me summarize.

The deep Decarbonization of energy systems rests on *three pillars*.

- The first
and conservation measures.*is energy efficiency* - The second is the
.*production of low carbon electricity* - And the third is the
.*switching of fuels from high to low carbon energy carriers*

I want to stress here that electricity plays a pivotal role in the deep Decarbonization scenarios because you see electricity in two out of the three pillars.

- First you see that electricity needs to be almost completely decarbonized and we’re going to come back to that in a moment.
- But also because electricity overall plays a more important role in energy consumption as fuel consumption switches from high carbon to low carbon options.

It is very important that you remember these three pillars because they really represent the *basic framework to think about the deep decarbonization of energy systems* in any circumstance. As we’re going to see in the next lectures, the precise options within each of these three pillars, but also their relative importance is going to vary of course from one country to the next. But these three pillars really represent the basic foundation to think about deep decarbonization.