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The greenhouse effect mechanism By S.M. Enzler MSc

Everyone knows the prediction that 'the greenhouse effect' will modify climate around the world.

But what exactly is the greenhouse effect? This page explains the mechanism.

Greenhouse effect - the mechanism

The sun radiates solar energy on earth. The larger part of this energy (45%) is radiated back into space. Greenhouse gases in the atmosphere (table 1) contribute to global warming by adsorption and reflection of atmospheric and solar energy. This natural phenomenon is what we call the greenhouse effect. It is agreed that the greenhouse effect is correlated with global temperature change. If greenhouse gases would not exist earthly temperatures would be below –18 oC.

Table 1: natural and anthropogenic greenhouse gases

Natural greenhouse gases

Anthropogenic emissions

H2O (water vapor)

CO2 (carbon dioxide)

CH4 (methane)

CH4 (methane)

CO2 (carbon dioxide)

N2O (nitrous oxide)

O3 (ozone)

N2O (nitrous oxide)

After the industrial revolution of the 1700’s the greenhouse effect was enhanced by greenhouse gas emissions of anthropogenic nature (table 1). The main source of anthropogenic greenhouse gas emissions is fossil fuel combustion. The contribution of greenhouse gases to the greenhouse effect varies (figure 2).

Figure 2: relative contribution of greenhouse gases
to the greenhouse effect (2004)

Non-governmental organizations (NGO’s) such as the IPCC (Intergovernmental Panel on Climate Change) are attempting to predict and project the severity and consequences of global climate change caused by the greenhouse effect. The IPCC expects that annual greenhouse gas emissions will double in the next 50-100 years. This results in a cascade of environmental effects.

Examples include:
- Melting of polar ice and oceanic expansion. This results in flooding of coastal areas, swamps, wetlands and river deltas. Some small islands may even vanish completely consequential to flooding
- Cold and warm gulf stream alteration caused by desalination of the Atlantic Ocean, possibly causing a new Ice Age
- Increase in number and severity of tropical storms and cyclones
- Flooding and erosion of agricultural plots. This damages crops and soils and decreases harvest
- Major shifts in ecosystems and decreasing biodiversity
- Evaporation of water supplies, causing drinking water scarcity
- Saltwater penetration of groundwater zones
- More extreme weather, causing hotter and drier summers and colder winters
- More contagious diseases because the environment is more positive for pathogens and some dangerous insects, such as the malaria mosquito

Ironically, an increase in greenhouse gases has been predicted to cause a cooling of the stratosphere. This phenomenon would occur because most thermal infrared is absorbed at low altitudes, and little is left over to warm the stratosphere. Additionally, at stratospheric temperatures CO2 emits more thermal infrared to space than it absorbs.

The greenhouse effect not only impacts the environment. It also has social and environmental consequences, such as large-scale migration and mitigation issues between countries.

Both political and environmental NGO’s try to gain support for the introduction and execution of solutions to the greenhouse effect. But despite the many actions of environmental organizations not every country accepts the greenhouse effect as a global environmental problem. Many believe that the theory holds some truth, but the consequences are largely exaggerated.

Related pages

Climate change glossary

Fossil fuels: characteristics and effects

Emissions and infrared absorption by greenhouse gases

Explanation of the IPCC SRES scenarios

The IPCC SRES scenarios: causes of climate change

The IPCC SRES scenarios: consequences of climate change

Overview of emission reductions for each country according to Kyoto

Possible policy measures to achieve Kyoto targets

Trading emission permits to achieve Kyoto targets

Discussions of the greenhouse effect

History of global warming

Perspectives on the greenhouse effect

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