The greenhouse effect

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effet de serre explication enjeux

Without the greenhouse effect, there would be no life on Earth, in any case, not as we know it. The average temperature would go down to -18°C or even lower. It is currently about +15 °C. This completely natural phenomenon therefore allows us to exist. How? Like a window pane, hence its name. Indeed, the solar radiation that arrives on Earth is mostly absorbed as infrared rays. Some atmospheric gases intercept these rays and send them back towards the ground which they then warm up. This is the greenhouse effect.

There is a direct relationship between the intensity of the greenhouse effect and how hot it is: the more gas there is, the hotter it is. For example, on Venus, the atmosphere contains many very powerful gases and the temperature is 460°C. Scientists have been aware of this relationship for a long time. As early as 1896, the Swedish researcher Svante Arrhenius calculated that double the amount of carbon dioxide (CO2) in the atmosphere would increase the planet’s average temperature by 4°C. This relationship has since been confirmed and it is better understood.

Man influences the greenhouse effect. The amount of CO2 in the atmosphere is measured in parts-per-million (ppm). It was stable until the Industrial Revolution, in the 18th century at around 270 ppm. Human activity has since generated a lot of emissions. In less than three centuries, this concentration has increased by about 30%; it reached 387 ppm in 2008. The study of ice cores in Antarctica shows that it has not been as high for 650 000 years.

Because greenhouse gas emissions linked to human activity (called anthropogenic) are the main cause of climate change, they must be limited. This is the main issue that will be debated during international negotiations and particularly, during the Copenhagen conference.


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