The Atmosphere and Climate Change

GCSE Chemistry · Chemistry of the Atmosphere

Today's atmosphere

The Earth's atmosphere has been roughly stable for about 200 million years:

~78% nitrogen
~21% oxygen
Small amounts of argon, carbon dioxide (~0.04%) and water vapour.

How the atmosphere evolved

Early atmosphere: intense volcanic activity released gases — mainly carbon dioxide, plus water vapour, and small amounts of methane and ammonia. Little or no oxygen (similar to Mars/Venus today).
Water vapour condensed as the Earth cooled, forming the oceans; lots of CO₂ dissolved into them.
Algae and plants evolved and carried out photosynthesis, which removed CO₂ and added oxygen over billions of years — allowing animals to evolve.
CO₂ also became locked up in sedimentary rocks (e.g. limestone) and in fossil fuels.

Greenhouse gases and global warming

Greenhouse gases — mainly carbon dioxide, methane and water vapour — trap heat in the atmosphere (the greenhouse effect), keeping Earth warm enough for life.

Human activities increase greenhouse gas levels:

Burning fossil fuels and deforestation raise CO₂.
Farming (livestock, rice) and landfill raise methane.

More greenhouse gases → more heat trapped → global warming and climate change.

Consequences of climate change

Rising sea levels (melting ice, thermal expansion) → flooding.
More extreme weather (storms, droughts, heatwaves).
Changes to habitats and the distribution of species.

Reducing the impact — carbon footprint

A carbon footprint is the total greenhouse gases produced by a product, service or activity. Ways to reduce it:

Use renewable energy and improve energy efficiency.
Carbon capture and storage.
Use fewer fossil fuels (electric transport), reduce, reuse and recycle.
Carbon offsetting (e.g. planting trees).

Atmospheric pollutants from fuels

Burning fuels also releases harmful pollutants:

Carbon monoxide (CO) — toxic, from incomplete combustion.
Soot (particulates) — cause breathing problems and global dimming.
Sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) — cause acid rain and respiratory problems.

Worked example

Explain how early photosynthesis changed the atmosphere.

Algae and plants used up CO₂ and released oxygen during photosynthesis over billions of years, so CO₂ levels fell and oxygen levels rose, eventually allowing animals to live. ✓

Common mistakes

Saying the early atmosphere was mostly oxygen — it was mostly carbon dioxide with little/no oxygen.
Confusing pollutants: CO (toxic), SO₂/NOₓ (acid rain), soot (particulates).
Forgetting the greenhouse effect is natural and necessary — the problem is the increase caused by humans.

Exam tips

Learn the current atmosphere percentages (78% N₂, 21% O₂).
Explain atmospheric change in terms of volcanoes → oceans → photosynthesis.
Match each pollutant to its problem, and list several ways to reduce a carbon footprint.

Key facts to remember

Atmosphere today: ~78% nitrogen, ~21% oxygen, ~0.04% CO₂; early atmosphere was mostly CO₂ from volcanoes.
Photosynthesis removed CO₂ and added O₂; CO₂ also locked in oceans, rocks and fossil fuels.
Greenhouse gases (CO₂, methane, water vapour) cause global warming; reduce your carbon footprint via renewables, efficiency and offsetting.