…, shaped by the ages, …

The natural greenhouse effect

The sun directs short-wave radiation towards us, most of which penetrates the atmosphere and reaches the Earth. The Earth absorbs the radiation and sends it back as long-wave thermal radiation. However, this long-wave thermal radiation is not able to leave the atmosphere again unimpeded, but is largely reflected back by greenhouse gases. The main gases responsible for this natural greenhouse effect are water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). They have almost the same effect as the glass roof of a greenhouse. Without them, the Earth would be about 33 °C colder, i.e. entirely frozen and uninhabitable for us. The amount of these greenhouse gases therefore has an impact on our climate. If the concentration of these gases increases, the atmosphere warms up more.

Man-made greenhouse effect

Greenhouse gases have increased greatly since the start of industrialisation, and so this is called the man-made (anthropogenic) greenhouse effect. This applies especially to the concentration of carbon dioxide (CO₂) and methane (CH4) in the atmosphere. Carbon dioxide escapes into the air when fossil fuels such as oil, coal and gas are burnt. Methane is released during the mining of fossil fuels, in livestock farming, at landfill sites and where rice is cultivated. Methane is also found in permafrost soils. So as global temperatures rise and the permafrost starts to melt, even more methane may be released, contributing further to the greenhouse effect. A gas that has even more impact on the climate than carbon dioxide and methane is nitrous oxide (N2O) which is also generated in agriculture, for example when nitrogen compounds break down in the soil. Most common fertilisers contain nitrogen. Even though the effect of CO2 as a greenhouse gas is far less than that of methane or nitrous oxide, carbon dioxide is responsible for most, 76%, of the man-made greenhouse gases. The reason for this is that far larger quantities of CO2 than of CH4 or N2O are entering the atmosphere. According to the IPCC (Intergovernmental Panel on Climate Change), the most powerful greenhouse gas is sulphur hexafluoride (SF6), which is used in high-voltage power systems. This gas originates in industrial processes and does not occur naturally. Since the atmosphere only contains very small amounts of it, its effect on global warming is low.

The future climate in Switzerland

It is expected that heatwaves will become more frequent and last longer, and record-breaking high temperatures will occur more often. At the same time, the number of frost days will reduce and extremely cold spells will become less severe and more infrequent. The zero-degree line will rise and with it the snow line. Especially at lower altitudes, rain will fall more often instead of snow. Measurements already show that the amount of heavy rain in winter is increasing. Climate modelling suggests a decrease in summer rainfall, leading to a greater risk of periods of drought, but this trend has not yet been backed up by the data. We certainly have to expect more frequent and more intense extreme weather conditions. This means that extremely torrential rain, storms, droughts and gales are likely to occur more often.

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