The Climate Equation: How to make progress on solving climate change

8 minute read

Updated on: 14 Dec 2020

This chapter introduces you to the “climate equation” - a concept that will help you understand how different solution ideas can contribute.

A framework for predicting (and reducing) emissions

Our greenhouse gas emissions are the result of individual people doing things like taking the train, heating their home, or buying a burger. Each activity or product releases emissions when used, when being made, and/or when transported.

This can be summarised very neatly in an equation:

Image of

If you just ran away because you don’t like maths, come back from behind the sofa! It’s a friendly equation and we’ll go through it step-by-step:

Total emissions = P x C x E

  • Total emissions = Global greenhouse gas emissions in a year
  • P = Population (the number of people on the planet)
  • C = Consumption (everything each person “consumes” in a year: buying a phone, driving a car etc. – anything you do!)
  • E = Greenhouse gas emissions per service (the amount of emissions caused before, during or after you use each service, which could be an activity or a physical product). The greenhouse gas that contributes the most to climate change is carbon dioxide (CO₂).

We can expand this to show the emissions from each individual service. This will be helpful later on.

Image of The Climate Equation

The Climate Equation

Total emissions have increased by a lot over the past decades, so this equation tells us that population (P), consumption per person per year (C), and/or emissions per service (E) must have increased.

Image of Population, consumption, and emissions per service trends

Population, consumption, and emissions per service trends

To stop climate change, we need the global emissions to be zero! If we could bring P, C, or E down to zero, then we would have no emissions – it’s basic maths: multiply anything by zero and you’ll get zero. Let’s explore the three options!

Image of Three options to reach zero emissions with the Climate Equation

Three options to reach zero emissions with the Climate Equation

How will the global population (P) change?

12 thousand years ago, there were 4 million people on the planet – nowadays, there are twice as many people living just in London!

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Historic population

About 2 hundred years ago the global population started to grow very rapidly. There are now about 7.7 billion of us and it’s predicted that we will reach about 9.7 billion by 2050.

From this graph you can see how fast the population is growing, and that it will start to plateau in the future around 2100:

Image of Past and future global population

Past and future global population

To get emissions down to zero, we clearly can’t have zero people! So, let’s look at the next option.

How has consumption (C) changed?

Energy use per person increased by 44% between 1971 and 2015 and people are eating more food (especially meat). In general, it is clear that resource use per person has been increasing rapidly.

Image of Energy use per person over time

Energy use per person over time

The Gross Domestic Product (GDP) is a measure of the total financial value of finished products and services produced in a country in a specific time period. The global GDP is the sum of GDPs from all countries and can be used to estimate total consumption.

Image of Contrasting high and low GDP

Contrasting high and low GDP

GDP can be standardized to account for inflation and the currencies of different countries. Global standardized GDP per person increased by 140% between 1970 and 2016:

Image of Increase in global GDP over time

Increase in global GDP over time

Should we decrease consumption (C)?

Today, there are around 1.3 billion people living in poverty. In order to give these people better lives, they require things like access to clean drinking water, electricity, and medicines. Therefore, in less developed countries we want consumption to increase to help improve people’s quality of life.

Image of Consumption can alleviate poverty

Consumption can alleviate poverty

But people in high-income countries can and should consume less. Each person can choose to (or be encouraged to) reduce their total consumption (i.e. decrease C). Perhaps even more importantly, people can shift to consuming products that cause lower emissions (i.e. products with lower E).

Image of Reduce and shift consumption

Reduce and shift consumption

However, since we can’t stop consuming things completely, there’s only one component left to target to get emissions down to zero…

Getting emissions per service (E) to zero

Unlike population and consumption, the emissions released per service have been decreasing over the past decades. This graph shows the decrease since the 1950s in CO₂ emissions per standardized $GDP per person:

Image of Decrease in emissions per $GDP

Decrease in emissions per $GDP

In other words, for every ‘thing’ that we consume, we cause less climate change than we did 50 years ago.

Engineers and scientists have created technologies that decrease the emissions from a lot of our consumption. Firstly, we can now generate energy in ways that produce far less greenhouse gas emissions. In 2018, just 8.5% of power came from low-emission sources like wind, solar and nuclear.

Moreover, we now have products and services that use less energy (e.g. light bulbs). Similarly, the average car in 1975 emitted about 422g of CO₂ for every kilometre it drove, whilst today, driving a kilometre emits only 217g of CO₂.

Zero-emission energy technologies such as renewables and advanced nuclear are the single most important priority right now. How successful we are depends on how much effort and investment we devote to improving and implementing sustainable technologies, and, also importantly, on what is physically possible!

Can we get E to zero for all products and services?

Unfortunately, no..

Whilst cars can be run on electricity generated by renewables or nuclear, commercial airplanes can’t yet be powered by electricity. Cows release a potent greenhouse gas called methane which can’t be prevented completely as far as we know.

To get these emissions down to zero, we have two choices:

  1. Reduce consumption e.g. don’t farm cows
  2. Take emissions back out of the air using technology or nature


For every service we use, greenhouse gas emissions need to be brought down as far as possible (bringing down E). Some products will always cause emissions. We either need to avoid those by shifting consumption or remove greenhouse gas from the air to make up for the damage.

Easier said than done, right?

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