Dramatic change

The changes to our climate that are happening now are attributed to a very steep rise in the concentration of a number of gases in the air. Concentrations of these gases, known as greenhouse gases (GHGs), have risen steeply since the industrial revolution in the nineteenth century and so human activity - how we live our lives - is the cause.

These gases are called greenhouse gases (GHGs) because they cause some of the heat from the sun to be trapped high in the sky and reflected back to Earth instead of escaping back out into space - which is similar to what happens in a greenhouse.

Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample.(Source: IPCC AR4, WGI, p.124)
Copyright IPCC, courtesy EPA.

This graph, showing GHG concentrations in the atmosphere during the last millenium, demonstrates the dramatic increase in these gases which began in the late 18th century and are continuing to rise in the twenty first century.These increases were initially triggered by the change from an economy based on manual labour to one based on machine manufacture and have continued to grow as all aspects of our lives have become mechanised.

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