Human Impacts On The Climate (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Human activity and climate change

• Human activities are contributing to the release of greenhouse gases, carbon dioxide and methane

• Carbon dioxide levels are increasing due to:

  • Burning fossil fuels (coal, oil and gas) for electricity generation, transport and industry

  • Deforestation means that there are fewer trees, removing less CO₂ from the atmosphere by photosynthesis

• Methane levels are increasing due to:

  • More waste being sent to landfill sites as the human population grows

  • Increased levels of farming 

Evidence for human-caused climate change

• These activities have led to a large rise in the concentration of CO₂ in the air over the last 150 years

• Over the same time, the average temperature of the Earth's surface has also risen

Graph to show the increase in carbon dioxide levels since 1700

Graph to show the increase in temperature levels since 1700

• The scientific consensus is that this is more than a correlation

  • The rise in greenhouse gas concentrations has caused the rise in temperature

• This consensus is based on systematic reviews of thousands of peer-reviewed publications

• Results are peer-reviewed so that other scientists can check findings for accuracy and validity

Modelling Climate Change

What is climate change?

• Climate describes the long-term patterns of weather in different parts of the world

• Climate change is shown by changes to patterns in measures such as:

  • Air temperature

  • Rainfall

  • Sunshine

  • Wind speed

How scientists model climate change

• Scientists analyse data on climate change using computer models based on the physics that describes the movements of mass and energy in the climate system

• Many complex changes on Earth affect the climate, and detailed data is not available from all parts of the world

• When predicting climate change, scientists have to make assumptions about future greenhouse gas emissions

  • This means that there are uncertainties in the predictions

• The data itself can show significant variation between years, making it difficult to identify clear trends

Limitations of historical data

• Advances in science and technology mean current levels of CO₂ and global temperatures can be determined with a high accuracy

• Historical data is much less accurate due to the lack of precise instrumentation and methods

• Fewer locations were measured, due to the lack of satellites and transport

• Methods to estimate past climate conditions include:

  • Analysis of the fossil record and tree rings

  • Analysis of gas bubbles trapped in ice from hundreds of thousands of years ago

• These methods are less precise than modern techniques and not representative on a global scale