Global climate change

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. You might talk about the weather being windy last week, or hotter last year than the year before. But unless you compare data for many years you cannot make a judgment about whether the climate is changing.

Climate change

The Earth’s climate has been constantly changing since the Earth was formed 4.6 billion years ago. This includes several ice ages and periods of much warmer global temperatures. Until 200 years ago, these changes were all caused by natural changes such as volcanic eruptions and changes in the energy that reaches the Earth from the Sun.

Global warming

Global warming is not the same as climate change. Global warming is usually used to describe the warming of the climate in the past 200 years, which the vast majority of scientists are almost certain has been caused by human activities.

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

The correlation between carbon dioxide and global warming

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. Compare the following graph to the one above.

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

The effects of global warming

The effects of global warming include:

We are already experiencing some of these effects. The consequences of global warming will affect billions of people, all around the world.

Question

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.