Global warming

Climate versus weather

Climate is different from weather because climate refers to the average temperature and cycles of weather over long periods of time – decades at least. People might talk about the weather being windy last week, or hotter last year than the year before. But unless the data is compared for many years a judgment cannot be made about whether the climate is changing.

Are humans causing global warming?

Human activities are increasing the amount of some greenhouse gases in the atmosphere. For example:

Methane is released by rice paddy fields
Methane is released by rice paddy fields

The amount of carbon dioxide in the atmosphere has increased over the past 150 years as a result of human activities.

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 concentration of carbon dioxide in the atmosphere passed 0.04% in 2016

Over the same time, the average temperature of the surface of the Earth has also increased.

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

One of the commonly used pieces of evidence that humans are causing global warming is that there is a strong correlation between the increase in global carbon dioxide levels caused by human activities and the increase in global temperatures over the same timescale.

Not everyone in the world agrees that humans are causing global warming by causing the release of greenhouse gases into the atmosphere. Some people believe that the current and ongoing rise in global temperatures is being caused by natural factors and cycles of climate change.

However, the vast majority of scientists do believe that humans are responsible for the increase in greenhouse gases and therefore global warming. This is because the majority of evidence in peer-reviewed journals supports the theory that human activities are causing an increase in greenhouse gases and this is causing global warming.

Climate science is complicated and it is difficult to predict what will happen to greenhouse gas emissions in the future, so scientists cannot be certain about global warming. Data is analysed using computer models based on the physics that describes the movements of mass and energy in the atmosphere and oceans. The climate is affected by many factors, and detailed data is not available from all locations on Earth, leading to uncertainties in the predictions.