Human Activities That Increase Greenhouse Gases Revision Notes | GCSE AQA Higher Chemistry

1. The Greenhouse Gas Problem

Earth's atmosphere is changing. Since the Industrial Revolution, human activities have pumped billions of tonnes of extra greenhouse gases into the air. This isn't just about polar bears - it's reshaping weather patterns, sea levels, and crop yields worldwide.

Two gases dominate this story: carbon dioxide (CO₂) and methane (CH₄). While CO₂ gets most attention, methane is actually 25 times more potent at trapping heat. Understanding where these gases come from is crucial for tackling climate change.

2. Carbon Dioxide - The Main Culprit

Carbon dioxide makes up about 76% of all greenhouse gas emissions. It's colourless, odourless, and comes mainly from one source: burning things that contain carbon.

The two biggest human activities that increase atmospheric CO₂ are:

1. Burning fossil fuels: Coal, oil, and natural gas power our electricity, heat our homes, and fuel our transport. When we burn them, carbon that was locked underground for millions of years gets released as CO₂.

2. Deforestation: Trees absorb CO₂ during photosynthesis. When we cut them down for agriculture or development, we lose these 'carbon sinks'. Worse, if we burn the wood, we release all the stored carbon at once.

This is where students often get confused about the carbon cycle. Let's check your understanding:

3. Methane - The Potent Problem

Methane (CH₄) might seem less important because there's less of it, but it's 25 times better at trapping heat than CO₂. A small increase in methane has a big impact on global warming.

The two main human activities that increase atmospheric methane are:

1. Agriculture (especially livestock): Cows, sheep, and other ruminants produce methane when they digest grass. Their stomachs contain bacteria that break down cellulose, releasing CH₄ as a waste product. Rice farming also produces methane because flooded rice fields create anaerobic conditions where methane-producing bacteria thrive.

2. Waste decomposition: Landfill sites and sewage treatment plants create perfect conditions for methane production. When organic waste decomposes without oxygen (anaerobic decomposition), bacteria produce CH₄ instead of CO₂.

Here's a calculation that shows why methane matters so much:

Worked example: Comparing Greenhouse Gas Impact

A farm releases 100 tonnes of methane and 2500 tonnes of CO₂ per year. Calculate the total 'CO₂ equivalent' impact if methane is 25 times more potent than CO₂.

1. Methane impact = 100 × 25 = 2500 tonnes CO₂ equivalent — Multiply by the potency factor
2. CO₂ impact = 2500 tonnes (already in CO₂ equivalent) — CO₂ is the baseline comparison
3. Total = 2500 + 2500 = 5000 tonnes CO₂ equivalent — Equal contributions despite much less methane by mass

Answer: 5000 tonnes CO₂ equivalent per year

Notice how 100 tonnes of methane has the same warming effect as 2500 tonnes of CO₂. This is why reducing methane emissions is so important for climate action.

4. The Evidence for Human Impact

How do we know humans are causing the increase in greenhouse gases? The evidence comes from multiple sources, and it's overwhelming.

Ice core data: Scientists drill deep into Antarctic ice to extract air bubbles from thousands of years ago. These show CO₂ levels were stable at around 280 ppm for millennia, then shot up to over 410 ppm since 1850.

Isotope analysis: Carbon from fossil fuels has a different isotopic signature than carbon from natural sources. By analysing the types of carbon in atmospheric CO₂, scientists can prove most of the increase comes from burning fossil fuels.

Temperature correlation: Global average temperatures have risen by about 1.1°C since pre-industrial times, closely matching the increase in greenhouse gas concentrations.

Based on this peer-reviewed evidence, the vast majority of climate scientists agree that human activities are causing Earth's atmosphere to warm, leading to global climate change.

5. Exam Technique and Common Mistakes

Exam questions on this topic often test your ability to recall specific human activities and explain the link between emissions and climate change. Here's how to get full marks:

Common exam mistakes to avoid:

Mistake 1: Writing 'pollution' instead of specific activities. Examiners want precise answers like 'burning coal' not vague terms like 'pollution'.

Mistake 2: Confusing correlation with causation. Don't just say 'temperatures are rising' - explain that greenhouse gases trap heat, causing the temperature increase.

Mistake 3: Forgetting that this is about HUMAN activities. Natural sources like volcanoes or animal respiration don't count for this topic.

Understanding these human impacts on greenhouse gas concentrations is essential for addressing climate change. The evidence is clear: our activities are changing the atmosphere, and this is driving global climate change. The next step is understanding what we can do about it.