In the past the Earth's climate has changed as a result of natural causes in our atmosphere.
The changes we are witnessing and those that are predicted are largely due to human behaviour. We are burning fossil fuels, and heating up the planet at the same time. We blow ever increasing amounts of carbon dioxide (CO2) into the atmosphere every year – 29 billion tonnes of it (2004) and rising – and this warms the globe.
Since the Industrial Revolution, humans have been burning fossil fuels on a massive scale.
We use this energy, almost without care for the consequences, to run vehicles, heat homes, conduct business, and power factories.
Burning fossil fuels releases CO2 stored millions of years ago as oil, coal or natural gas. In the last 200 years we have burned a large part of these stores, resulting in an increase in CO2 in our atmosphere. The destruction of our forests also releases CO2 stored in trees and in the soil.
The increase of CO2 in the atmosphere thickens the 'greenhouse blanket', with the result that too much heat is trapped into the Earth's atmosphere. This causes global warming: global temperatures rise and cause climate change.
Looking at the numbers
Data from the World Resources Institute (WRI) show that humans have added 2.3 trillion tonnes of CO2 to the atmosphere in the last 200 years. Half of this amount was added in the last 30 years.
The largest absolute increase in CO2 emissions occurred in 2004, when burning fossil fuels alone added more than 28 billion tonnes to the atmosphere. Source: WRI, Navigating the numbers, based on data from IEA, EIA, Marland et al, and BP.
Overall, the concentration of CO2 in the atmosphere has increased by 31% since 1750, i.e. since the Industrial Revolution.
CO2 emissions are now around 12 times higher than in 1900 as the world burns more and more coal, oil and gas for energy. A 1999 study by Mann et al. shows the dramatic increase in temperature in the Northern Hemisphere in the last 50 years. This well-known hockey stick curve has been validated by numerous other scientists.