Climate change

Human activities are causing an increase in the amounts of greenhouse gases in the atmosphere. The table shows some common sources of carbon dioxide and methane.

GasHuman causes
Carbon dioxideBurning fossil fuels
MethaneCattle farming
Rice picker in an Indian paddy field
Methane is released by rice paddy fields

Enhanced greenhouse effect

The concentration of carbon dioxide in the atmosphere has increased in the last 200 years.

Graph shows how carbon dioxide has increased between 1700 and 2000. In the year 1700 there was 0.028% CO2 in the atmosphere, but at around 1850 this began to rise. By 2000, the percentage of CO2 was at 0.035, an increase of 0.007%

The extra carbon dioxide is causing an enhanced greenhouse effect, greater than would happen naturally. There is a correlation between the increase in atmospheric carbon dioxide concentration, and temperature change.

As the concentration of carbon dioxide has increased, the global average temperature has generally increased too.

Graph showing how the global average temperature has changed from around 1870 - 2000. The line graph shows an increase in global temperatureThe Earth's average temperature has gradually increased over time

There is a correlation between the consumption of fossil fuels and the amount of carbon dioxide in the atmosphere (and also between the consumption of fossil fuels and the average temperature of the atmosphere). While a correlation between two factors does not necessarily mean that one causes the other, the majority of climate scientists believe that the increase in atmospheric carbon dioxide caused by burning more fossil fuels is causing the increase in atmospheric temperature and changes in the Earth's climate. A report from the Intergovernmental Panel on Climate Change (UN, 2014) stated that there is a 95% probability that human activity has caused an increase in the Earth's temperature. It cites human-produced greenhouse gases such as carbon dioxide as major contributors to the observed increase in our planet's temperature over the past 50 years.

Some scientists disagree. They might claim that climate change is a result of a natural cycle.

Climate change

The climate describes the average weather over a long time and over a large area. The enhanced greenhouse effect is leading to climate change. The effects of this include:


Suggest two reasons why climate change leads to rising sea levels.

Water from melting glaciers and polar ice enters the oceans. As the Earth's temperature increases, seawater warms up and expands.

There are international treaties aimed at reducing the emissions of carbon dioxide and other greenhouse gases. However, even if these emissions could fall significantly, it would take a long time for the Earth's temperature to stabilise then decrease. In the meantime, there are ways to mitigate the effects of climate change. These include:

  • building flood defences to manage floods from rivers and seas
  • building irrigation systems to provide water in droughts
  • planting different crops, better adapted to a new climate

These steps are expensive, need to be on a large scale, and may themselves harm the environment.