Increased levels of greenhouse gases
Natural gases, including atmospheric water vapour, methane and carbon dioxide, act as an insulating blanket for the earth by retaining heat from the sun which keeps the earth warm. This is known as 'the greenhouse effect', and the gases that cause it are known as 'greenhouse gases'. Without these gases, the earth would be much colder than it is.
Increased concentrations of greenhouse gases in the earth's atmosphere cause global temperatures to rise. This is known as 'global warming'.
Since the industrial revolution, emissions of greenhouse gases, mainly carbon dioxide from the burning of fossil fuels, have increased sharply.
There is overwhelming scientific evidence that points to human activities, such as the continued burning of fossil fuels, as being mainly responsible for the current increased levels of greenhouse gases in the atmosphere. Global warming caused by human activity is sometimes referred to as 'anthropogenic global warming' or 'AGW'.