The Greenhouse Effect

The greenhouse effect is fairly basic science, simple enough in principle to explain in elementary science curriculum. Sunlight passes through the transparent glass of a greenhouse roof. When it reaches an opaque surface, some of the energy is converted to heat which cannot escape as readily. As a result, temperatures increase inside the greenhouse. In the model, atmospheric gasses act like a glass roof and elevate the Earth’s temperature.

In reality, the greenhouse effect is more complex. Greenhouse gases do not form a physical blanket-like barrier, and energy is transferred several ways. The greenhouse gas effect moderates our planet’s temperature; for example, without greenhouse gasses, temperature on the moon can rise 250°C between dawn and lunar noon.

The two greatest greenhouse gases by volume are water vapor and CO2, carbon dioxide. The amount of greenhouse gas in the atmosphere varies widely with temperature, altitude and latitude, but on average water vapor accounts for about 70% and CO2 between 4-8%. Other gases such as methane and ozone account for very small amounts.

Carbon Emissions
CO2 is the most controversial of the greenhouse emissions. It gets complicated because increases in CO2 will improve the efficiency of water use in many food crops and can make trees grow faster. Obviously, in an area with a lot of vegetation, changing the amount of CO2 will affect the amount of water vapor. Although carbon emissions are also caused by plant and animal respiration, biological decay, and volcanic eruptions, regulations focus almost entirely on the burning of fuels.

The Political Atmosphere
The UNFCCC, United Nations Framework Convention on Climate Change, has called for reducing greenhouse gases and is especially targeting carbon emissions from fossil fuels. A carbon footprint is an estimate of the total set of greenhouse gas emissions of an individual or group. Because these numbers are in dispute, the politics associated with the greenhouse effect can easily become as heated as the sun’s energy.

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