The Greenhouse Effect
The term 'Greenhouse Effect' is commonly used to describe the
increase in the Earth's average temperature that has been recorded
over the past 100 years. However, without the 'natural greenhouse
effect', life on Earth would be very different to that seen today.
The 'natural greenhouse effect'
The Earth receives its life sustaining warmth from the Sun. On its way
to the Earth's surface most of the heat energy passes through the
Earth's atmosphere, while a smaller proportion is reflected back
into space.
The energy warms the Earth's surface, and as the temperature increases,
the Earth radiates heat energy (infrared energy) back into the atmosphere.
As this energy has a different wavelength to that coming from the sun,
some is absorbed by gases in the atmosphere.
There are four main naturally occurring gases that are responsible for
the Greenhouse Effect; water vapour,
carbon dioxide, methane
and nitrous oxide. Of these gases, water vapour has the largest effect. Once these gases
absorb energy, the gas particles begin to vibrate and they radiate energy
in all directions, including approximately 30% of it back towards Earth.
The other two important greenhouse gases are ozone
and halocarbons.Although Although most of the greenhouse gases occur naturally in the atmosphere, some are man-made and the most well-known of these are fluorocarbons. Since the industrial revolution, human activities have also resulted in an increase in natural greenhouse gases, especially carbon dioxide. An increase in these gases in the atmosphere enhances the atmosphere’s ability to trap heat, which leads to an increase in the average surface temperature of the Earth.
 As a result, the Earth’s average surface temperature is kept at about 15C by the blanket of atmosphere that surrounds it. Without this, the temperature would be about minus 18C – too cold for life. The gases keep the Earth warm in a similar (but not identical) way as a greenhouse keeps plants warm.
Interactive
greenhouse effect animation
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