An uneven greenhouse effect
11/10/11

It’s a first! A harmonisation procedure for observation of the atmosphere has shown that the concentrations of methane and nitrous oxide, two greenhouse gases, showed variable trends from one site to another. 

At the end of the 19th century the Swedish chemist Svante August Arrhenius published an article which later became famous in which he predicted an overall global warming of 5°C if the concentration of carbon dioxide doubled. More than a century later, our knowledge of the atmosphere has evolved considerably, but this figure, although more refined, is still current.

Atmosphere
The temperature and the climate on Earth are fixed by its atmosphere, the main factor of the energy balance between solar radiation which reaches the surface of the Earth and that which it re-emits. Part of this re-emitted infrared radiation remains trapped in the atmosphere, allowing for mild temperatures at the surface. The greenhouse effect is therefore a natural phenomenon. Yet for several decades, human activity has significantly changed the chemical composition of the atmosphere, leading to an increase in greenhouse gases and, through this, an extra greenhouse effect described as being caused by human activity.

The most important greenhouse gas today resulting from human activity and also the best known is without doubt CO2. But it is far from being the only one: also present in lesser quantities in the atmosphere are methane (CH4) and nitrous oxide (N2O) which is still sometimes called laughing gas –also belong to the group of molecules of concern. They are the subject of a recent publication (1) in which the authors attempt to ascertain in fine detail the temporal evolution of their concentrations. Among these, is Emmanuel Mahieu, a researcher with the Infrared Group of Solar and Atmospheric Physics (GIRPAS) at the University of Liège.

(1) Angelbratt J. et al., A new method to detect long term trends of methane (CH4) and nitrous oxide (N2O) total columns measured within the NDACC ground-based high resolution solar FTIR network. Atmos. Chem. Phys., 11, 6167-6183, 2011.

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