Global climate change: An increase in average global temperature is a major cause of climate change.

The idea

Average global temperature is calculated from many weather stations, ocean buoys and satellite measurements over long periods. When this average rises, the extra thermal energy drives a chain of effects: ice sheets and glaciers melt, sea levels rise, and warmer oceans and air alter evaporation, rainfall patterns and storm behaviour. These shifts in long-term weather patterns are what scientists call climate change. The temperature rise is therefore treated as a major cause because it supplies the energy and the melting that produce the wider changes. A single hot summer is weather, not climate; evidence comes from decades of data and from patterns across the whole planet.

What earns the marks

• Average global temperature is a long-term mean calculated from worldwide measurements, not the temperature of one place or one day.
• A rise in this average adds thermal energy to the Earth system, melting ice and expanding ocean water so sea levels rise.
• Warmer air and oceans change evaporation and precipitation, shifting rainfall patterns and the frequency or intensity of some extreme weather.
• Climate change means a sustained shift in long-term weather patterns, so the temperature rise is a major cause rather than a single weather event.
• Evidence for the trend comes from comparing many decades of data from multiple sources, which reduces the effect of local variation.

Common mistakes and how to put them right

• Confusing weather with climate.

  Put it right: Weather is short-term and local, while climate is the long-term pattern over decades.

• Saying the temperature rise is the only cause of climate change.

  Put it right: It is a major cause, and other factors such as changes in greenhouse gas concentrations also contribute.

• Treating one cold winter as proof that global warming is not happening.

  Put it right: A single season is weather and does not overturn a long-term global trend.

Exam tips

• Define average global temperature before explaining its effects, so your answer shows the term is understood.
• Use a cause-and-effect chain such as warmer average temperature → ice melt and thermal expansion → sea level rise.
• Quote the idea of long-term patterns when distinguishing climate change from a one-off weather event.