The greenhouse effect affects you. Do you affect it?
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The Earth’s climate has always undergone change. These climate changes have until recently come about by natural means. Now it looks as if, for the first time ever, we are facing a global climate change caused by our own activities.
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The natural greenhouse effect
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The natural greenhouse effect keeps the Earth’s mean temperature about 34 °C higher than it would have been otherwise. Today, the mean temperature is about 15 °C. Without the natural greenhouse effect, the global mean temperature would thus be -19 °C.
The natural greenhouse effect comes from the presence of clouds and “greenhouse gases” such as CO2 and methane.
The greenhouse gases and clouds have the ability to let in incoming heat from the sun and at the same time trap the outgoing heat from the Earth. The energy from the Earth’s surface is then released in all directions. Some of this heat then returns back to the Earth’s surface.
The greenhouse gases thus make it possible for more of the heat to be kept in the Earth’s atmosphere, while less disappears back into space.
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The human-induced greenhouse effect
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Since pre-industrial times (about 1750), the concentration of CO2 has increased by about 31 percent, and the concentration of methane (CH4) has increased by about 151 percent. The increase comes from emissions from human activities, and intensifies the natural greenhouse effect.
The increase in the atmosphere’s CO2 concentration is the most important factor in the human-induced intensification of the greenhouse effect. Human emissions of CO2 come mainly from consumption of fossil fuels (coal, oil and gas) and deforestation in tropical areas. |
 Emissions from human activity make up only a small part of the greenhouse gases in the atmosphere, and their effect is small – compared to, for example, the effect of the naturally occurring water vapor. But nature’s own emissions of greenhouse gases are included in the carbon cycle – where, for example, decomposing trees emit CO2 and living trees absorb CO2 through photosynthesis. Our CO2 emissions – from, for example, burning fossil materials – do not have a natural role in this carbon cycle. When we use fossil fuels, we retrieve carbon that has been stored far below ground or in the ocean floor for eons. This carbon is not part of the cycle and thus provides a surplus of CO2 that stays in the atmosphere for a very long time. |
Useful links
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Global consequences
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Coming soon
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