11.4 Global Warming

This topic explains global warming — the increase in Earth's average temperature due to human activities — and its connection to the greenhouse effect.

Definition

Global Warming

The warming of the atmosphere due to our influence on the greenhouse effect is called global warming.

Simple explanation: Global warming is the rise in Earth's temperature caused by human activities.

Greenhouse Gases

Gases like water vapour, methane, and carbon dioxide act in a similar way in the atmosphere. These gases are called greenhouse gases.

Simple explanation: Greenhouse gases trap heat in the atmosphere.

Greenhouse Effect

The process where greenhouse gases act like a blanket, trapping some of the heat energy in the lower atmosphere, is referred to as the greenhouse effect.

Simple explanation: The greenhouse effect is the natural process that keeps Earth warm enough for life.

Main Idea

The increasing use of fossil fuels and deforestation have led to an increase in the levels of CO₂ in the air.

• Some of it is absorbed by the Earth's surface (vegetation, oceans, land).
• This warms the Earth.
• As the Earth's surface heats up, it emits energy in the form of infrared radiation.
• Greenhouse gases absorb this energy.
• These gases re-radiate some of the infrared radiation.

As a result, greenhouse gases act like a blanket, trapping some of the heat energy in the lower atmosphere. This reduces thermal energy loss to space and helps to regulate the Earth's temperature.

Without this effect, the Earth would be much colder — making it difficult for life to exist.

Simple explanation: Greenhouse gases keep Earth warm by trapping heat. Without them, Earth would be too cold for life.

Core Concept

The Greenhouse Effect — Step by Step

Simple explanation: The greenhouse effect is like a blanket around Earth — it lets sunlight in but traps some of the heat.

How Human Activities Enhance the Greenhouse Effect

• Burning fossil fuels
• Deforestation
• Industrial processes

This additional increase in greenhouse gases is enhancing the natural greenhouse effect. This is leading to a significant increase in atmospheric temperature, causing global warming and climate change.

The higher the concentration of greenhouse gases in the air, the greater the greenhouse effect and the greater the increase in temperature.

Simple explanation: More greenhouse gases → more heat trapped → higher temperatures → global warming.

Global Warming vs Greenhouse Effect

Simple explanation: The greenhouse effect is natural and necessary; global warming is the result of too much greenhouse effect caused by humans.

Detailed Explanation

The Natural Greenhouse Effect

The greenhouse effect is a natural phenomenon of the Earth's energy distribution mechanism.

• Sunlight (visible light) passes through the atmosphere and reaches the Earth's surface.
• The Earth's surface absorbs this energy and warms up.
• The warm Earth emits energy as infrared radiation (heat).
• Greenhouse gases in the atmosphere absorb some of this infrared radiation.
• They re-radiate it in all directions — some back to Earth, some to space.
• This traps heat in the lower atmosphere.
• Earth stays warm enough for life.

Simple explanation: The greenhouse effect is like a car with closed windows on a sunny day — heat gets in but doesn't all get out.

How Humans Are Enhancing the Greenhouse Effect

• Burning fossil fuels (coal, oil, natural gas) → releases CO₂.
• Deforestation → fewer trees to absorb CO₂.
• Industrial processes → release CO₂ and other greenhouse gases.
• Agriculture → livestock produce methane (CH₄).
• Landfills → decomposing waste produces methane.

Simple explanation: Humans add extra greenhouse gases, making the blanket thicker and Earth warmer.

The Greenhouse Effect — Analogy from the Book

The book gives an analogy with a greenhouse:

> "Greenhouses are constructed from glass or transparent polymer films. Sunlight can pass through these materials and is used by the plants for photosynthesis. The plants radiate some energy in the form of infrared or heat radiations which cannot pass through these materials and is reflected back. As a result, the atmosphere inside the greenhouse becomes hot enough to promote plant growth. The temperature inside a greenhouse can be 10 °C to 15 °C higher than outside."

Simple explanation: A greenhouse traps heat inside, just like greenhouse gases trap heat in Earth's atmosphere.

Effects of Global Warming

If global warming continues, then:

Simple explanation: Global warming leads to higher temperatures, changing rainfall patterns, melting ice, and rising sea levels.

Concept Assessment Exercise 11.5 (from the Book)

1. Define global warming.

Answer: The warming of the atmosphere due to our influence on the greenhouse effect is called global warming.

2. List some effects of global warming.

• Temperature of the Earth will gradually increase.
• Climate change (affecting rainfall patterns, causing floods and droughts).
• Polar ice may melt, causing sea levels to rise.
• The atmosphere becomes hotter.

3. List some substances that are responsible for global warming.

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Water vapour
• Nitrous oxide (N₂O)
• Other greenhouse gases

4. Establish the link between greenhouse effect and global warming.

Answer: The greenhouse effect is a natural phenomenon that keeps Earth warm. Human activities have increased the concentration of greenhouse gases, enhancing the greenhouse effect. This enhanced greenhouse effect is causing global warming — the increase in Earth's average temperature.

Intermediate Level

The Greenhouse Effect — In Detail

• Carbon dioxide (CO₂) — main greenhouse gas from human activities.
• Methane (CH₄) — from livestock, landfills, wetlands.
• Water vapour (H₂O) — natural greenhouse gas.
• Nitrous oxide (N₂O) — from agriculture and industry.

• Sunlight (visible light) reaches Earth.
• Earth's surface absorbs it and warms up.
• Earth emits infrared radiation (heat).
• Greenhouse gases absorb this infrared radiation.
• Some energy is re-radiated back to Earth.
• Earth stays warm.

Simple explanation: The greenhouse effect is like a blanket — it keeps Earth warm.

Why the Greenhouse Effect Is Important

• Earth's average temperature would be about −18 °C instead of +15 °C.
• The planet would be too cold for life as we know it.
• Oceans would freeze.

Simple explanation: The greenhouse effect is essential for life — we just don't want too much of it.

Human Activities That Enhance the Greenhouse Effect

Effects of Global Warming — In Detail

• Earth's average temperature rises.
• Heat waves become more frequent.

• Rainfall patterns change.
• Some regions get more rain (floods), others get less (droughts).

• Ice sheets and glaciers melt.
• Sea levels rise.
• Coastal areas may be flooded.

• Habitats change.
• Some species may become extinct.
• Coral reefs may bleach.

Mitigation Strategies

Note: These strategies are covered in more detail in Section 11.7.

Important Points

• - Global warming: the warming of the atmosphere due to our influence on the greenhouse effect.
• - Greenhouse gases: water vapour, methane, carbon dioxide, nitrous oxide.
• - Greenhouse effect: natural phenomenon that keeps Earth warm by trapping heat.
• - Human activities increase greenhouse gases → enhance the greenhouse effect → global warming.
• - Human activities: burning fossil fuels, deforestation, industrial processes, agriculture.
• - Effects of global warming:
• - Temperature increase
• - Climate change (floods, droughts)
• - Melting polar ice, rising sea levels
• - Hotter atmosphere
• - Without the greenhouse effect, Earth would be too cold for life.

Remember

• - Global warming = warming of atmosphere due to human influence on greenhouse effect.
• - **Greenhouse gases** = CO₂, CH₄, H₂O, N₂O.
• - Greenhouse effect = natural blanket that keeps Earth warm.
• - Human activities increase greenhouse gases.
• - Effects: temperature increase, climate change, melting ice, rising sea levels.
• - Without greenhouse effect, Earth would be too cold for life.

Common Mistakes

• 1. Confusing global warming with the greenhouse effect. The greenhouse effect is natural; global warming is the enhancement of it by human activities.
• 2. Thinking the greenhouse effect is entirely bad. It is necessary for life — we just don't want too much of it.
• 3. Thinking only CO₂ causes global warming. Other gases like methane and nitrous oxide also contribute.
• 4. Thinking global warming only means hotter weather. It also causes climate change — floods, droughts, and sea level rise.
• 5. Forgetting that deforestation contributes. Trees absorb CO₂; cutting them down increases CO₂.
• 6. Thinking the greenhouse effect only happens on Earth. It happens on any planet with greenhouse gases in its atmosphere.

Quick Revision

• Global warming: the warming of the atmosphere due to our influence on the greenhouse effect.
• Greenhouse gases: water vapour, methane, carbon dioxide, nitrous oxide.
• Greenhouse effect: a natural phenomenon of the Earth's energy distribution mechanism; gases like water vapour, methane, and carbon dioxide trap heat in the lower atmosphere, reducing thermal energy loss to space.
• Without the greenhouse effect, the Earth would be much colder, making it difficult for life to exist.
• Human activities (burning fossil fuels, deforestation, industrial processes) have been increasing the concentration of greenhouse gases, enhancing the natural greenhouse effect → global warming and climate change.
• Effects of global warming:
• Temperature of the Earth will gradually increase.
• Climate change, affecting rainfall patterns, causing floods and droughts.
• Polar ice may melt and cause significant increase in sea levels.
• Atmosphere becomes hotter.
• Greenhouse analogy: like a greenhouse, greenhouse gases trap heat, warming the planet.

60-Second Revision

• Global warming = warming of atmosphere due to human influence on greenhouse effect.
• **Greenhouse gases** = CO₂, CH₄, H₂O, N₂O.
• Greenhouse effect = natural blanket that keeps Earth warm.
• Human activities increase greenhouse gases.
• Effects: temperature increase, climate change, melting ice, rising sea levels.
• Warning: the greenhouse effect is natural and necessary; global warming is caused by too much of it.