Chapter 1

Introduction

For thousands of years, human progress has been closely linked to energy. Fire provided heat and protection, wind powered sailing ships, water wheels drove early machinery, and coal helped launch the Industrial Revolution. Later, oil, natural gas and electricity transformed transport, manufacturing and everyday life. Each transition allowed humanity to do more.

Today, energy powers almost every part of modern civilisation. It keeps hospitals operating, moves people and goods around the world, produces food, heats and cools buildings, powers factories and connects billions of people through digital technology. At the same time, global demand for energy continues to grow as populations increase, economies develop and living standards improve.

The challenge facing humanity is therefore not to stop using energy. It is to provide the enormous amount of energy modern society depends upon while dramatically reducing the greenhouse gas emissions produced along the way. Understanding why requires looking at the energy system we have built, how it affects the Earth's climate and why reaching net-zero emissions has become one of the defining engineering challenges of the twenty-first century.

A World Powered by Energy

The modern world requires an extraordinary amount of energy. Every time a light is switched on, a car moves, a building is heated, steel is manufactured or a data centre processes information, energy is being converted from one form into another. Energy is so deeply embedded in everyday life that it is easy to forget how dramatically our ability to access it has changed.

Early societies relied primarily on human labour, animals, wood, wind and flowing water. These resources were useful, but the amount of energy they could provide was limited. The widespread use of fossil fuels changed that. Coal could release large quantities of concentrated energy, oil provided a compact liquid fuel that could easily be transported, and natural gas provided a convenient source of heat and later became an important fuel for electricity generation.

These resources helped enable industrialisation on a scale that would previously have been impossible. Factories became larger, transport became faster, electricity networks spread across countries, agricultural productivity increased and goods could be manufactured and transported around the world. Access to abundant energy became one of the foundations of modern prosperity.

Today, billions of people depend on reliable energy every second of every day, while developing economies continue building homes, factories, transport networks and electricity systems of their own. The world therefore faces an unusual challenge: we need to transform the way energy is produced at the same time as humanity continues demanding more of it.

Our Dependence on Fossil Fuels

For more than a century, much of the world's energy system was built around three resources: coal, oil and natural gas. There are good reasons why they became so successful. Fossil fuels contain large quantities of stored chemical energy, can be transported and stored, and can be used whenever required. These characteristics made them extremely useful for everything from electricity generation and heating to transport and industrial manufacturing.

Coal helped power factories and electricity stations, oil transformed transport through petrol, diesel and aviation fuels, and natural gas became widely used for heating, electricity generation and industrial processes. Together, these fuels helped build much of the infrastructure and prosperity that modern society enjoys today.

But there is an important consequence. Fossil fuels contain carbon that has been stored underground for millions of years. When they are burned, that carbon reacts with oxygen and is released into the atmosphere primarily as carbon dioxide, or CO₂. In its simplest form, the process can be represented as:

Carbon + Oxygen → Carbon Dioxide + Energy

The energy released is extremely useful. The carbon dioxide released alongside it creates the longer-term problem. Humanity has built an energy system capable of producing enormous amounts of useful energy, but one that also releases greenhouse gases on an enormous scale.

The challenge of the energy transition is therefore not simply to stop using fossil fuels. It is to replace the useful services they provide with alternatives capable of delivering reliable and affordable energy with far lower greenhouse gas emissions.

The Greenhouse Effect

To understand why carbon dioxide matters, we first need to understand how the Earth stays warm. Energy from the Sun reaches Earth primarily as electromagnetic radiation. Some of this incoming sunlight is reflected back into space by clouds, the atmosphere and the Earth's surface, while the rest is absorbed by the land and oceans, warming the planet.

The Earth then releases energy back towards space in the form of infrared radiation. However, not all of this outgoing energy escapes immediately. Certain gases in the atmosphere, including carbon dioxide, methane and water vapour, absorb and re-emit some of this infrared radiation. These are known as greenhouse gases, and the process is known as the greenhouse effect.

Importantly, the greenhouse effect itself is completely natural. Without it, Earth would be far colder and the planet as we know it would be unable to support the same ecosystems and life. The problem arises when the concentration of greenhouse gases in the atmosphere increases.

Adding more greenhouse gases changes the balance between the energy arriving from the Sun and the energy leaving Earth. Less heat escapes to space than otherwise would, causing the climate system to warm until a new energy balance is reached. By burning fossil fuels and increasing the concentration of carbon dioxide in the atmosphere, human activity is strengthening this natural greenhouse effect.

Why the Climate Is Warming

The Earth's climate has never been completely constant. Over geological history, temperatures have changed because of variations in the Earth's orbit, volcanic activity, changes in solar output and other natural processes. What makes the current period different is the dominant cause and the speed at which the change is occurring.

Since industrialisation, humanity has burned enormous quantities of coal, oil and natural gas, transferring carbon that had been stored underground into the atmosphere. At the same time, land-use changes such as deforestation have reduced some of the natural systems capable of absorbing carbon dioxide. The result has been a substantial increase in atmospheric greenhouse gas concentrations and a strengthening of the greenhouse effect.

As the Earth accumulates additional heat, the consequences extend far beyond simply making each day slightly warmer. Rising temperatures can influence rainfall patterns, increase the severity of extreme heat, contribute to the melting of glaciers and ice sheets, raise sea levels and place additional pressure on ecosystems and communities around the world.

Climate change is therefore not simply an environmental problem. It can affect infrastructure, agriculture, water supplies, economies and the way cities and energy systems themselves must be designed. Because the production and use of energy account for a large share of global greenhouse gas emissions, transforming the energy system lies at the centre of efforts to limit further warming.

This leads to an important question. If reducing emissions slows climate change, why is the goal net zero rather than simply reducing emissions by 20%, 50% or even 90%? The answer lies in the way carbon dioxide accumulates in the atmosphere.

Why Net Zero Matters

A useful way to understand net zero is to imagine filling a bathtub while the drain is partially open. Water flows into the bath from the tap while some water leaves through the drain. If water enters faster than it leaves, the level continues rising. Turning the tap down slows the rate at which the bathtub fills, but the water level still continues to rise. To stop it rising completely, the amount of water entering must eventually equal the amount leaving.

Atmospheric carbon dioxide behaves in a similar way. Human activities add carbon dioxide to the atmosphere, while forests, oceans and other natural processes remove some of it. As long as humanity adds more carbon dioxide than these processes remove, the amount accumulating in the atmosphere continues increasing. Reducing emissions slows that accumulation, but reaching approximately net-zero carbon dioxide emissions is what stops humanity from continuing to add to it overall.

This is what makes net zero fundamentally different from simply reducing emissions. Net zero does not necessarily mean that absolutely no greenhouse gases are emitted anywhere. Some emissions may be extremely difficult or expensive to eliminate entirely, particularly from activities such as agriculture, aviation and certain industrial processes. Instead, the aim is to reduce emissions as far as practical and balance the remaining emissions with an equivalent amount removed from the atmosphere.

Those removals might come from natural systems such as forests or from engineered technologies designed to capture carbon dioxide. The important idea is the balance: when the amount of carbon dioxide added to the atmosphere is approximately matched by the amount removed, net emissions reach zero.

Reaching this point requires changes across almost every part of the modern energy system. Electricity generation, transport, heating, manufacturing and heavy industry all currently depend to varying degrees on fossil fuels. The transition is therefore much larger than simply replacing one type of power station with another. It requires changing how energy is produced, transported, stored and ultimately used.

A Growing World Still Needs Energy

There is another side to the challenge. While greenhouse gas emissions need to fall, humanity's need for energy is not disappearing. The global population continues to grow, while billions of people around the world are seeking higher standards of living and greater access to the technologies that many developed economies already take for granted.

As economies develop, energy use often increases. Homes gain refrigerators and air conditioning, people travel further, factories manufacture more products, hospitals gain more advanced equipment and cities build transport networks, water systems and other infrastructure. Access to reliable electricity itself can dramatically improve quality of life by supporting healthcare, education, communication and economic development.

The solution to climate change therefore cannot simply be asking the world to stop using energy. For many communities, greater access to energy is essential for future development. Instead, the challenge is to meet those growing energy needs while progressively reducing the amount of greenhouse gas emitted to provide them.

Clean electricity can play a major role in achieving this because many activities that currently burn fossil fuels directly can instead be powered using electricity. An electric vehicle can replace petrol or diesel with an electric motor, while a heat pump can replace the direct combustion of gas for heating. Industrial processes can also increasingly use electricity instead of fossil fuels where technically practical.

As electricity generation becomes cleaner, electrification allows that low-carbon electricity to spread into other areas of the economy. The energy transition therefore involves two enormous changes happening at the same time: cleaning the electricity system and expanding what electricity is used for.

Energy Security

Climate change is one of the strongest reasons for transforming the world's energy system, but it is not the only one. Energy also has enormous economic and geopolitical importance. Countries that depend heavily on imported coal, oil or natural gas can be exposed to disruptions in global supply, while wars, political disputes, infrastructure failures and sudden changes in international markets can all affect the availability and price of fuel.

Renewable resources behave differently. A country cannot control the international price of oil or natural gas, but sunlight falling within its borders does not need to be imported, and neither does the wind. Once solar panels, wind turbines and supporting infrastructure have been constructed, they can generate electricity from domestic energy resources without requiring a continuous supply of fuel.

That does not make renewable energy completely independent of global supply chains. Solar panels, batteries, wind turbines, transformers and transmission lines all require raw materials, manufacturing and infrastructure. However, it changes the nature of energy security. Instead of continually importing fuel, countries can invest more heavily in assets capable of harvesting energy available within their own borders.

At the same time, the transition must remain affordable and reliable. An energy system that dramatically reduces emissions but cannot provide dependable or reasonably priced electricity would create problems of its own. The challenge is therefore to balance three closely connected objectives: sustainability, energy security and affordability, while maintaining the reliability modern society expects every second of every day.

The Need for an Energy Transition

Taken together, these challenges explain why the world's energy system is beginning to change. Modern civilisation was built using abundant fossil fuels, and enormous amounts of existing infrastructure still depend upon them. At the same time, global demand for energy continues to grow as populations increase, economies develop and new technologies become part of everyday life.

Yet continuing to release greenhouse gases indefinitely would continue changing the Earth's climate. The goal is therefore not to abandon energy or reverse human development. It is to build a better energy system: one capable of providing reliable and affordable energy to billions of people while progressively eliminating the greenhouse gas emissions responsible for long-term warming.

Achieving this will require changes across electricity, transport, buildings and industry. There will be no single technology capable of solving every part of the problem, but electricity is likely to sit at the centre of much of the transition. As electricity generation becomes cleaner, more activities can be electrified, allowing low-carbon energy to replace fossil fuels far beyond the electricity grid itself.

This transformation is known as the energy transition: the gradual shift from an energy system dominated by fossil fuels towards one increasingly built around low-carbon electricity, renewable energy, energy storage, electrification and other technologies capable of reducing emissions. It is one of the largest engineering transformations humanity has ever attempted.

Looking Ahead

The need for change is becoming increasingly clear, but an equally remarkable story is already unfolding in response. Technologies that once supplied only a tiny fraction of the world's electricity are now being deployed on an enormous scale.

Solar farms stretch across landscapes, wind turbines stand hundreds of metres tall and millions of buildings now generate electricity directly from their rooftops. 

In the next chapter, we'll explore the rise of renewable energy and discover how solar moved from a niche technology to one of the defining technologies of the global energy transition.