Human activities produce greenhouse gases that cause the enhanced greenhouse effect and global warming; evidence and consequences of human-caused climate change, and the range and uncertainty of future projections.

What this dot point is asking

This is Edexcel GCSE Geography B (1GB0) Paper 1, Section A (Topic 1, Hazardous Earth). Edexcel expects you to explain how human activities in industry, transport, energy and farming produce greenhouse gases (carbon dioxide and methane) that cause the enhanced greenhouse effect and global warming; the evidence that human activity is changing the climate; the possible consequences for people; and the range and uncertainty of future projections for temperature and sea level rise to 2100. Questions often use projection graphs, so you must read and describe data as well as explain the science.

The enhanced greenhouse effect

The atmosphere naturally keeps the Earth about 33 degrees Celsius warmer than it would otherwise be. Short-wave solar radiation passes through the atmosphere and warms the surface; the surface re-emits energy as long-wave (infrared) radiation, and greenhouse gases absorb some of this and radiate it back down, trapping heat. Without this natural greenhouse effect the planet would be frozen.

The key human activities are: energy (burning coal, oil and gas to generate electricity), transport (petrol and diesel vehicles, aviation and shipping), industry (factories, cement and steel) and farming (livestock and rice produce methane). Deforestation makes it worse twice over: burning trees releases stored carbon, and fewer trees remain to absorb carbon dioxide.

Evidence for human-caused climate change

Several independent lines of evidence point to recent, human-driven warming.

The consequences for people follow from these changes: coastal flooding and the loss of low-lying land and homes (for example in Bangladesh and small island states such as the Maldives), water and food insecurity where rainfall becomes less reliable (the Sahel), the spread of some diseases, and the cost of adapting with sea defences and new crops.

Future projections and uncertainty

Climate scientists use computer models to project the future, but the results are given as a range, not a single figure.

Projections of global temperature to 2100 span roughly 1 to 4 degrees Celsius of additional warming, and sea level rise projections span tens of centimetres to over a metre. This range exists for three reasons: we cannot be certain how much greenhouse gas humans will emit (it depends on future population, economic growth and energy choices); feedback loops are hard to predict (for example melting ice exposes dark ocean that absorbs more heat, amplifying warming, while extra cloud could reflect more sunlight); and the climate system is complex, so models differ in exactly how sensitive the climate is to extra carbon dioxide.

Try this

Q1. Explain how deforestation contributes to climate change. [4 marks]

• Cue. Burning or clearing trees releases stored carbon dioxide, and removing the forest reduces the carbon dioxide that vegetation would have absorbed, so atmospheric carbon dioxide rises and warming increases.

Q2. Give two pieces of evidence that recent climate change is caused by human activity. [2 marks]

• Cue. Rising global temperatures matching rising carbon dioxide, plus declining Arctic sea ice, warming oceans and sea level rise, or more frequent extreme weather.