Sciences

• The greenhouse effect occurs naturally, providing a habitable climate.
• Atmospheric concentrations of some of the gases that produce the greenhouse effect are increasing due to human activity and most of the world's climate scientists consider that this is a significant part of the cause of observed climate change.
• The oceans are a critical part of the climate system, with vastly greater thermal capacity than the atmosphere. A small, slow increase in their temperature is significant.
• Over one-third of human-induced greenhouse gas emissions come from the burning of fossil fuel to generate electricity. Nuclear power plants do not emit these gases.

The "greenhouse effect" is the term used to describe the retention of heat in the Earth's lower atmosphere (troposphere) due to concentrations of certain trace gases and water vapour in the atmosphere. These gases are generally known as greenhouse gases*. Concentrations of some of them have increased steadily during the 20th century and into the 21st, with CO2 rising from under 300 ppm to 400 ppm. A large part of the increase in all greenhouse gases is attributed to human sources, i.e. it is anthropogenic, hence the term ‘anthropogenic global warming’ (AGW).