AP Environmental Science

## Learning Outcomes

- Explain why economic development often increases total energy demand
- Distinguish between total energy use, per capita energy use, energy intensity, and carbon intensity
- Describe why developing economies often rely heavily on fossil fuels during industrialization
- Use the Kaya identity to explain why emissions can rise even when efficiency improves
- Evaluate why development does not always lead to permanent fossil fuel dependence
- Connect rising fossil fuel use to air pollution, greenhouse gas emissions, and climate change

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand how development affects global energy consumption, with a focus on the following syllabus points:

- Know that global energy use rises as countries industrialize, urbanize, and electrify
- Identify why coal, oil, and natural gas often meet new energy demand during development
- Explain the difference between total energy use and per capita energy use
- Understand that fossil fuels still supply about **80%** of global energy demand
- Distinguish between energy intensity and carbon intensity
- Understand how the **Kaya identity** links population, affluence, energy use, and carbon emissions
- Explain the environmental consequences of rising fossil fuel combustion, including air pollution and climate change
- Recognise that development can also include efficiency gains and renewable expansion, so fossil reliance is a pattern, not an absolute rule

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why does economic development usually increase energy demand?
2. What is the difference between total energy use and per capita energy use?
3. Why do many developing countries increase fossil fuel use as they industrialize?
4. How does the Kaya identity help explain rising carbon dioxide emissions?
5. Why is it inaccurate to say that development always increases fossil fuel reliance forever?

## Introduction

Economic development usually improves living standards, but it also changes how societies use energy. As countries industrialize, build infrastructure, expand transport, and bring electricity and clean cooking to more people, their total demand for energy tends to increase sharply. In many cases, that new demand is first met by **fossil fuels** because coal, oil, and natural gas are energy-dense, established, and often easier to scale quickly than alternatives.

For AP Environmental Science, this topic matters because it links energy systems to pollution, climate change, and sustainability. You need to understand not just that energy use rises with development, but _why_ this happens, _how_ it affects emissions, and _when_ the pattern can begin to change.

> **Key Term: global energy consumption**
> The total energy used worldwide across households, industry, transportation, and other sectors.

### Why development increases energy demand

Development changes both the structure of an economy and the daily lives of its population. In a low-income region, many households may use relatively little commercial energy. Cooking may rely on traditional biomass, transport may be limited, and fewer homes may have appliances, air conditioning, or reliable electricity. As incomes rise, this changes fast.

The main cause chain is straightforward:

- economic growth increases production and incomes
- higher incomes increase demand for goods and services
- supplying those goods and services requires more electricity, transport, heating, cooling, and industrial activity
- total energy use rises

Industrialization is especially important. Factories, mining, refining, cement production, and large-scale agriculture all require significant energy inputs. The industrial sector is a major energy consumer because manufacturing physical goods takes far more energy than simply moving information.

Urbanization also raises energy demand. Cities need roads, rail systems, street lighting, water treatment, sewage treatment, construction materials, and cooling systems. Apartment blocks, offices, hospitals, and shopping areas all need electricity. Even if dense cities can be more efficient per person than scattered rural development, the process of building and operating them still increases overall energy use.

Electrification is another major driver. Electricity is only one part of total energy use, but it is the fastest-growing form of end-use energy in many places. A household moving from no reliable electricity to regular access begins using lighting, refrigeration, charging, fans, and possibly electric cooking or cooling. That is a major welfare gain, but it also pushes demand upward.

Transport growth matters too. Development often means more trucks moving goods, more private vehicles, more buses, more trains, and more air travel. Oil products remain especially important in transport because liquid fuels are easy to store and move.

> **Key Term: economic development**
> Growth in income, industry, infrastructure, and living standards that usually increases access to goods, services, and modern energy.
>
> **Key Term: energy demand**
> The total amount of energy a society wants to use for services such as electricity, transportation, heating, cooling, and industry.

A common mistake is to treat this as only a population story. Population growth matters, but development also raises energy use _per person_. A country can keep the same population and still use much more energy if each person has more appliances, better housing, more travel, and greater consumption.

> **Test Tip:** In APES questions, build a clear chain: development -> more industry/transport/electricity use -> more fuel combustion -> more air pollution and greenhouse gas emissions.

### Why that extra demand is often met by fossil fuels

Development does not just increase energy demand. It often increases **fossil fuel reliance** specifically, at least for a period. The reason is not that fossil fuels are inherently better for the environment. It is that they are often cheaper, more energy-dense, easier to transport, and supported by existing infrastructure.

Coal has historically supplied a large share of global electricity. It is abundant in some regions, can generate power at scale, and fits large centralized electric grids. Oil dominates much of transport because gasoline and diesel are convenient liquid fuels. Natural gas is widely used for heating, electricity generation, and industrial processes, and is often seen as cleaner than coal in terms of some air pollutants, even though it still produces carbon dioxide and methane leaks can be a serious climate problem.

This means developing countries often follow an "energy ladder" pattern. Households and economies move from traditional biomass and limited energy access toward commercial fuels and electricity. In the short to medium term, that frequently means more coal, oil, and gas use before cleaner systems are built out.

> **Key Term: fossil fuel reliance**
> Dependence on coal, oil, and natural gas to meet energy needs.

There are several reasons fossil fuels are commonly chosen during development:

- they have high **energy quality** and high net energy yield
- technology for using them already exists
- infrastructure for extraction, transport, and combustion may already be in place
- they can often provide large amounts of power continuously
- political systems may support them because they provide jobs and tax revenue

The current global pattern supports this. Fossil fuels still provide most of the world’s energy. That means when energy demand rises in emerging and developing economies, a large part of the increase is still often met through fossil fuel systems.

However, APES students must avoid oversimplification. Development does **not** always mean more fossil fuel use in every case. Some countries build wind, solar, hydroelectric, or geothermal capacity rapidly. Some expand renewable electricity faster than coal use. Some improve efficiency enough to slow fuel demand growth. The key idea is that fossil-fuel dependence is a common pathway, not a universal law.

This is especially true because modern development includes stronger pressure for cleaner systems than during the early Industrial Revolution. Countries today are developing in a world where climate change, urban air pollution, and renewable technology are already major issues.

> **Key Term: energy transition**
> A change in how a society produces and uses energy, often from traditional biomass and fossil fuels toward cleaner and more efficient systems.
>
> **Test Tip:** If an answer choice says development "always" increases fossil fuel use, be cautious. APES often rewards more precise wording such as "often," "usually," or "in many developing economies."

### Total use, per capita use, and the measures students confuse

Students often mix up total energy use with per capita energy use. They are related, but not identical.

Total energy use is the energy consumed by the whole society. Per capita energy use is total energy use divided by population.

> **Key Term: per capita energy use**
> Total energy use divided by population; the average energy use per person.

A country with a very large population may have high total energy use even if average use per person is modest. A wealthy country with a smaller population may have lower total use but much higher per capita use.

This distinction matters because development can raise both, but not always at the same rate. If population grows rapidly and energy access expands only slowly, total use may rise strongly while per capita use rises more gradually. If a country becomes wealthier without much population growth, per capita energy use may jump a lot.

Students also confuse **energy intensity** and **carbon intensity**.

> **Key Term: energy intensity**
> The amount of energy used per unit of GDP.
>
> **Key Term: carbon intensity**
> The amount of carbon dioxide emitted per unit of energy used.

Energy intensity is about efficiency. If a country can produce more GDP with less energy, its energy intensity falls. Carbon intensity is about fuel mix. If a country shifts from coal toward lower-carbon sources, its carbon intensity falls.

These can move in different directions. A country may become more energy-efficient but still rely on coal. In that case, energy intensity falls but carbon intensity stays high. Or a country may switch toward cleaner energy without major efficiency gains. Then carbon intensity falls even if energy intensity changes little.

A simple comparison helps:

- lowering **energy intensity** = using energy more efficiently
- lowering **carbon intensity** = using cleaner energy sources

This is why development and emissions are not linked in a simple one-step way. Development may improve efficiency, but if total production, transport, and consumption rise fast enough, total emissions can still increase.

### Using the Kaya identity to explain emissions growth

The best way to organise this idea is with the Kaya identity.

> **Key Term: Kaya identity**
> A way to break down carbon dioxide emissions into population × GDP per person × energy per unit of GDP × carbon dioxide per unit of energy.

Written fully:

CO2 emissions = Population × (GDP / Population) × (Energy / GDP) × (CO2 / Energy)

This can be read as:

- population
- multiplied by GDP per capita
- multiplied by energy intensity
- multiplied by carbon intensity

This is powerful because it shows why emissions can rise even when some parts improve.

### Worked example

Suppose a country changes over time like this:

- population rises by **10%**
- GDP per capita rises by **30%**
- energy intensity falls by **15%**
- carbon intensity falls by **5%**

To estimate the overall change in emissions:

1. Convert each change into a multiplier
   - population: 1.10
   - GDP per capita: 1.30
   - energy intensity: 0.85
   - carbon intensity: 0.95

2. Multiply them  
   1.10 × 1.30 × 0.85 × 0.95 = 1.154725

3. Convert back to a percentage  
   1.154725 means emissions are about **15.5% higher**

So even though the country became more energy-efficient and slightly cleaner in its fuel mix, emissions still rose because population and affluence increased more strongly.

This is exactly the pattern often seen in developing economies. Growth in income and energy services can outweigh gains in efficiency.

> **Test Tip:** In an FRQ, use Kaya logic even if you are not asked to write the full formula. Explain that rising GDP per capita and population can outweigh falling energy intensity or carbon intensity.

A common APES error is to say, "Efficiency improves, so emissions must fall." Not necessarily. Efficiency reduces one driver, but total output may still rise.

### Why this matters environmentally

When development increases fossil fuel use, the environmental effects are large. Coal, oil, and natural gas combustion release carbon dioxide, the major long-lived greenhouse gas associated with climate change. Combustion also produces air pollutants directly or indirectly, including particulates, sulfur dioxide, and nitrogen oxides depending on the fuel and technology used.

That leads to several linked consequences:

- more greenhouse gas emissions
- stronger greenhouse effect
- higher average global temperatures
- changing precipitation patterns, sea level rise, and ecological stress

It also creates more immediate local problems:

- outdoor air pollution
- respiratory illness
- acid deposition from sulfur and nitrogen compounds
- particulate pollution that harms cardiovascular and respiratory health

This is why the topic is not simply economic. Development brings real human benefits: electricity, refrigeration, cleaner cooking, transport, and industry all improve quality of life. But if those gains are built mostly on fossil fuels, they can also increase environmental damage.

A high-quality APES answer should show both sides. Expanding energy access is socially valuable. The issue is the fuel source and the speed of the transition to cleaner systems.

### Why the pattern can change over time

Development often increases fossil reliance first, but that does not mean the pattern lasts forever. As economies grow, they may gain the capital, technology, and policy capacity to invest in:

- renewable energy
- more efficient appliances and buildings
- cleaner transport systems
- modern electrical grids
- cleaner cooking technologies

This is why some developing countries may partly "leapfrog" older pathways. Rather than following the exact historical path of early industrial countries, they may add solar, wind, and efficient technology much earlier.

Still, leapfrogging has limits. A country may add lots of renewable electricity but still depend on oil in transport and natural gas or coal in industry. That is why APES responses should avoid a simplistic yes/no answer.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Global energy consumption is the total energy used across all sectors worldwide
- Economic development usually raises energy demand through industrialization, urbanization, electrification, and transport growth
- Developing economies often increase fossil fuel use because coal, oil, and gas are energy-dense and supported by existing infrastructure
- Fossil fuels still provide most global energy, so rising demand often means rising fossil fuel combustion
- Total energy use and per capita energy use are not the same measure
- Energy intensity measures energy use per unit of GDP, while carbon intensity measures CO2 emitted per unit of energy
- Lower energy intensity means improved efficiency, but lower carbon intensity means cleaner fuels
- The Kaya identity explains emissions as the product of population, GDP per capita, energy intensity, and carbon intensity
- Emissions can still rise even if efficiency improves, if population and affluence increase faster
- Development does not always mean permanent fossil dependence because renewables and efficiency can grow too
- Rising fossil fuel use increases greenhouse gas emissions and often worsens air pollution
- APES answers should present development as a trade-off between improved human welfare and environmental costs

## Key Terms and Concepts

- global energy consumption
- economic development
- energy demand
- fossil fuel reliance
- energy transition
- per capita energy use
- energy intensity
- carbon intensity
- Kaya identity


Global Energy Consumption - Development increases fossil reliance