Greenhouse Effect Write-up
What is the “greenhouse effect”?
Let’s take a look at something smaller first: a greenhouse. We do not need greenhouses in Singapore, but temperate countries such as Canada do. This is because the climate in Singapore is naturally warm enough for plants to grow in abundance. Temperate countries that do not have this kind of warm climate all year round require greenhouses. Greenhouses are made of glass, and they can effectively trap enough thermal energy (heat) to stimulate the perfect conditions for the growth of plants.
How, then, does a greenhouse work?
The Sun’s heat passes through the glass roof of the greenhouse. The infra-red radiation given out by the plants and fittings inside the greenhouse, however, have a much longer wavelength than the heat waves from the Sun, and the glass prevents the transmission of longer wavelengths, hence effectively trapping the heat within the greenhouse. Due to this, the temperature inside the greenhouse rises over time. The “greenhouse effect” occurs in a similar manner.
The greenhouse effect is the process “in which the emission of infrared radiation by the atmosphere warms a planet’s surface” (Wikipedia, [website], available at http://en.wikipedia.org/wiki/Greenhouse_effect , 29th February, 2008). It was discovered in 1824, but only investigated quantitatively in 1896. It involves three main processes: the reflection, absorption and radiation of heat.
The Sun gives out infra-red radiation that passes through the Earth’s atmosphere. Some of it—approximately thirty percent—is reflected back into space, while the rest (about seventy percent) is absorbed by the Earth. This absorbed energy warms the surface of the Earth, and then is radiated back toward space. However, greenhouse gases in the atmosphere, namely methane, carbon dioxide, nitrous oxide, water vapor, ozone and halocarbons, prevent the transmission of longer wavelengths, just like the glass of the greenhouses. Since the returning infra-red radiation is of longer wavelength, the greenhouse gases in the atmosphere absorb most of this energy and fire it back at the Earth’s surface. In preventing the escape of heat, the Earth’s average temperature slowly rises.
Earth is not the only planet that experiences this process. Venus’s atmosphere is made up almost entirely of carbon dioxide (ninety-six percent), and the rest is made up of carbon monoxide, argon, sulfur dioxide, water vapor and nitrogen. Since carbon dioxide is a greenhouse gas, it traps the thermal energy that reaches the surface of Venus and prevents it from being transmitted back into space. Venus’s greenhouse effect has caused the planet’s surface and lower atmosphere to become one of the hottest places in the solar system.
To see how the enhanced greenhouse effect works and how it affects us, take a look at the post “The Enhanced Greenhouse Effect”.
For more information on some of the terms used in this entry, visit the category Glossary of Terms.
