Electromagnetic waves - EdexcelEmission and absorption of infrared radiation

All bodies (objects) emit and absorb infrared radiation. They do this whatever their temperature. The hotter the body:

• the more infrared radiation it gives out in a given time
• the greater the proportion of emitted radiation is visible light

Factors affecting temperature - Higher

The temperature of a body is linked to the balance between the amount of radiation absorbed and emitted.

Factors affecting the Earth’s temperature - Higher

The temperature of the Earth depends on many factors including the concentration of greenhouse gases such as water vapour, methane and carbon dioxide.

The Earth’s temperature also depends on the rates at which light radiation and infrared radiation are:

• absorbed by the Earth’s surface and atmosphere
• emitted by the Earth’s surface and atmosphere

When visible light and high frequency infrared radiation are absorbed by the surface of the Earth, the planet’s internal energy increases and the surface gets hotter. Some of this energy is transferred to the atmosphere by conduction and convection.

The Earth also radiates lower frequency infrared radiation. Some of this infrared radiation is transmitted through the atmosphere back out into space, and some is absorbed by greenhouse gases in the atmosphere. The greenhouse gases emit infrared radiation in all directions – some out into space and some back towards Earth, which is then reabsorbed.

The greenhouse effect

The ‘greenhouse effect’ caused by naturally occurring greenhouse gases, such as water vapour, stabilises the surface temperature of Earth. This allows the planet to support life.

However, human activities such as deforestation and the burning of fossil fuels are releasing additional carbon dioxide. This causes more infrared radiation to be ‘trapped’ and reabsorbed by the Earth’s surface. This enhanced greenhouse effect is causing global temperatures to increase, leading to climate change.