After 1900, industrialization, population growth, and globalization put massive pressure on the planet, leading to deforestation, desertification, declining air and water quality, and competition over resources. Greenhouse gases and pollution fueled debates about climate change, including disagreements over its causes and over who should be responsible for addressing it.
Why This Matters for the AP World History Exam
Topic 9.3 fits squarely into Unit 9, which covers about 8 to 10 percent of the exam. The main skill here is causation: you should be able to explain the causes and effects of environmental changes from 1900 to the present.
This topic connects well to other Unit 9 themes, especially technology in 9.1, economic globalization in 9.4, and reform movements in 9.5. On the exam, environmental change is useful for building causation arguments and for showing continuity and change over time. You might also use it as evidence in a longer essay that traces how industrialization created both progress and new problems. Treat people like Rachel Carson or events like the Paris Agreement as examples you can apply, not as required names you must memorize.
Key Takeaways
- Human activity after 1900 drove deforestation, desertification, falling air quality, and heavier use of the world's fresh water supply.
- As these resources became strained, competition over them grew more intense than in earlier periods.
- The release of greenhouse gases and pollutants sparked debates about the nature and causes of climate change.
- Population growth, urbanization, industrialization, and globalization are the main causes you can point to when explaining environmental change.
- Environmental debates are political as well as scientific, often dividing industrialized nations and developing nations.
- The strongest answers connect technology's benefits to its environmental costs instead of treating them separately.
Causes of Environmental Degradation
Several connected factors drove large-scale environmental change after 1900:
- Population growth: The global population grew from roughly 1.6 billion in 1900 to over 8 billion by the 2020s, putting heavy pressure on land, water, and energy.
- Urbanization: Expanding cities harmed habitats and raised emissions.
- Industrialization: Factories, mines, and chemical production introduced new pollutants and intensified resource extraction.
- Globalization: Worldwide demand for consumer goods expanded deforestation, fishing, and shipping, raising carbon output.
The same technological systems that made life easier for many people also produced environmental consequences that were not planned for.
Deforestation and Desertification
Deforestation
Large-scale tree removal harms biodiversity, rainfall patterns, and soil stability. A well-known example is the Amazon Rainforest, where deforestation sped up in the late 20th century because of:
- Cattle ranching
- Logging
- Soybean farming
Losing forest cover reduces the Earth's ability to absorb carbon, which feeds into climate change.
Desertification
Desertification is the process of once-fertile land turning into desert. Common causes include:
- Overgrazing by livestock
- Soil erosion
- Deforestation
- Climate shifts
This has been especially common in parts of Africa, South Asia, and Central Asia, where farmers have been displaced and ecosystems disrupted.
Pollution and Environmental Toxins
Pollution rose sharply with industrial and transportation emissions. Harmful substances entered soil, air, and water through:
- Factory runoff
- Pesticides and chemical fertilizers
- Waste from oil drilling and mining
- Carbon emissions from burning fossil fuels
| Pollution Type | Source | Consequences |
|---|---|---|
| Air Pollution | Cars, factories, power plants | Respiratory diseases, smog, acid rain |
| Water Pollution | Industrial waste, oil spills, sewage | Contaminated drinking water, marine death |
| Soil Pollution | Pesticides, deforestation, landfills | Loss of fertile land, toxins in crops |
Pollution does not only damage ecosystems. It also worsens public health, especially in crowded urban areas.
Climate Change and Global Warming
Most scientists point to human activity as the main cause of accelerated global warming, especially the release of greenhouse gases:
- Carbon dioxide (CO2): From burning coal, oil, and gas
- Methane (CH4): From livestock and landfills
- Nitrous oxide (N2O): From fertilizers and industrial processes
These gases trap heat in the atmosphere through the greenhouse effect, which contributes to:
- Rising global temperatures
- Melting glaciers and rising sea levels
- Ocean acidification
- More frequent extreme weather events
Climate has shifted naturally throughout Earth's history, but the speed of change since 1900 is tied closely to industrial output. This is the heart of the debate the topic asks you to understand: people argue about the nature and causes of climate change, not just whether it is happening.
Global Responses to Environmental Change
As awareness grew, governments and international groups created treaties and policies to limit damage and push for sustainability. These are useful examples you can apply on the exam, not required names.
Kyoto Protocol (1997)
- An international treaty aimed at reducing greenhouse gas emissions.
- Applied mainly to developed nations.
- Some major emitters, including the United States, later withdrew, and developing countries like China and India had different obligations because of their development status.
Paris Agreement (2015)
- Set emission reduction targets for participating countries.
- Focused on keeping global warming well below 2 degrees Celsius above pre-industrial levels.
- Marked a major moment in international cooperation on climate.
Oil Pollution Act (1990), United States
- Passed after the Exxon Valdez oil spill.
- Required oil companies to pay for environmental damage caused by spills.
- Led to tighter regulations and more industry oversight.
Modern Environmental Debates
Environmentalism today is political as well as scientific. Common debates include:
- The role of industrialized versus developing nations in causing and fixing climate change
- Balancing economic growth with sustainability
- The ethics of how much societies consume
- Climate migration and environmental justice
These debates connect directly to the resource competition described in this topic, since arguments over fresh water, land, and energy often reflect deeper questions about fairness and responsibility.
How to Use This on the AP World History Exam
Causation
When a question asks about environmental change after 1900, structure your answer around clear causes and effects. Causes include population growth, urbanization, industrialization, and globalization. Effects include deforestation, desertification, weaker air quality, strained fresh water supplies, and sharper competition over resources.
Free Response
If you bring environmental change into a longer essay, tie it to technology and economics. A strong line of reasoning shows how the same advances that raised productivity and connected the world also created pollution and climate debates. Use specific examples as evidence, then explain how that evidence supports your argument.
Using Sources Effectively
Documents about the environment often carry a clear point of view, such as an activist, a government, or an industry group. Use the source's purpose and audience to explain why it frames climate change or pollution the way it does. This is especially useful because the topic centers on debates, where different groups disagree about causes and responsibility.
Common Trap
Do not turn this into a science essay. The exam wants historical reasoning about causes, effects, and competing arguments, not a technical explanation of the greenhouse effect.
Common Misconceptions
- Climate change debate means scientists disagree that it is happening. The historical debate is mostly about its nature, causes, and who is responsible, not about whether the planet is warming.
- Environmental damage is only a recent problem. Resource use and pollution have long histories, but after 1900 the scale and intensity of competition over resources reached new levels.
- Only industrialized nations matter in this story. Deforestation, desertification, and water shortages affected and involved many regions, including the Global South, which shaped global debates about fairness.
- Treaties like Kyoto or Paris are required AP content. They are helpful examples you can apply, but the topic itself focuses on the causes and effects of environmental change and the debates it produced.
- Listing environmental problems is enough. You need to connect causes to effects and explain the debates, not just name deforestation, pollution, and climate change.
Related AP World History Guides
Vocabulary
The following words are mentioned explicitly in the College Board Course and Exam Description for this topic.Term | Definition |
|---|---|
air quality | The measure of pollutants and contaminants in the atmosphere that affect human health and the environment. |
climate change | Long-term shifts in global temperatures and weather patterns, often attributed to the release of greenhouse gases and other human activities. |
deforestation | The large-scale removal or clearing of forests, typically to make way for other land uses or due to human activity. |
desertification | The process by which fertile land gradually transforms into desert, often due to drought, climate change, or unsustainable land use practices. |
environmental changes | Alterations to natural systems and ecosystems resulting from human activity or natural processes. |
fresh water consumption | The use and depletion of freshwater resources from sources such as rivers, lakes, and groundwater for human activities. |
greenhouse gases | Gases released into the atmosphere that trap heat and contribute to global warming and climate change. |
resource competition | The struggle between groups or nations for access to and control of limited natural resources. |
Frequently Asked Questions
How does AP World History treat global warming?
AP World History treats global warming as part of broader environmental change after 1900. Focus on historical causes, effects, and debates rather than technical climate science.
What caused environmental change after 1900?
Major causes include industrialization, population growth, urbanization, globalization, fossil fuel use, and expanding demand for land, water, energy, and consumer goods.
What were major environmental effects after 1900?
Important effects include deforestation, desertification, air and water pollution, climate change, fresh water strain, resource competition, and public health problems.
What does the AP World topic mean by environmental debates?
Environmental debates include arguments over the causes of climate change, who is responsible for pollution, how to balance economic growth with sustainability, and whether industrialized or developing nations should carry more responsibility.
Are Kyoto and the Paris Agreement required AP World examples?
They are useful examples, but the core topic is about causes, effects, and debates over environmental change after 1900. Use treaties only when they help support your argument.
How should I use environmental change on the AP World exam?
Use it for causation and continuity/change arguments. Connect technology, industrialization, and globalization to specific environmental effects and the debates those effects produced.