What Causes Global Warming? GCSE Biology
Learn what causes global warming for AQA GCSE Biology: how carbon dioxide and methane strengthen the greenhouse effect, plus the roles of deforestation and peat.
Global warming is the long-term rise in Earth’s average temperature. It happens when increasing amounts of greenhouse gases, particularly carbon dioxide and methane, trap more heat in the atmosphere. The term climate means the long-term pattern of weather, so global warming is about a long-term change, not one unusually hot day.
How do greenhouse gases warm Earth?
Sunlight reaches Earth and warms its surface. The warm surface then gives out energy as infrared radiation. Greenhouse gases absorb some of this outgoing radiation, so less energy escapes into space. The gases then transfer energy back towards the Earth’s surface and lower atmosphere. This is the greenhouse effect.
The greenhouse effect happens naturally and helps keep Earth warm enough for life. However, rising greenhouse gas levels make the effect stronger. More energy is retained in the Earth system, so the average temperature increases over time. This enhanced greenhouse effect causes global warming.
Why are greenhouse gas levels rising?
Burning fossil fuels releases carbon dioxide into the atmosphere. Deforestation also contributes to rising carbon dioxide levels. Fewer trees means less carbon dioxide is removed from the atmosphere by photosynthesis. In addition, the decay or burning of peat releases carbon dioxide.
Methane is another greenhouse gas. It can be produced when biological material decays without oxygen, a process called anaerobic decay. Increasing levels of carbon dioxide and methane contribute to global warming.
Exam point
For AQA GCSE Biology, link each cause to its effect clearly: more greenhouse gas in the atmosphere means more outgoing infrared radiation is absorbed, so more energy is retained and Earth’s average temperature rises over time.
A common mistake is to say that global warming means every place becomes hotter every day. Weather can change quickly from day to day, while global warming describes a long-term trend in average temperature. Also, do not say that greenhouse gases stop all energy escaping into space; they absorb some outgoing infrared radiation, which strengthens the greenhouse effect.
