Impacts on the climate system

Question 1

Radiative processes

Answer 1

 Source of energy that drives the climate system is radiation from the Sun (see Fig. 9.2)

 Incoming is the short wave solar radiation (Fig. 9.2 left side); outgoing is the long wave terrestrial radiation (Fig. 9.2 right side) and the sensible and latent heat transfers (Fig. 9.2 middle)

 The atmosphere contains several trace gases, so-called greenhouse gases, which absorb and emit infrared radiation.

 Most important greenhouse gases are: water vapour, carbon dioxide, ozone, nitrous oxide, and methane

 The energy component labeled ‘back radiation’ is a key indicator of the greenhouse effect

 Thus greenhouse gases trap heat within the atmosphere. This mechanism is called the natural greenhouse effect.

Question 2

Radiative forcings

Answer 2

 In an equilibrium climate state the average net radiation at the top of the atmosphere is zero (Rin=Rout).

 A change in either the incoming solar radiation or the outgoing infrared radiation changes the net radiation. The corresponding imbalance is called “radiative forcing”.

 The climate system must react to restore the balance. A positive radiative forcing tends to warm the surface, whereas a negative radiative forcing tends to cool it.

 Radiative forcing can be caused by natural and anthropogenic factors (see Fig. 9.3).

 Natural factors are the change in solar irradiance or increased aerosol concentrations caused by volcanic eruptions.

 Anthropogenic factors are the change of the concentration of greenhouse gases, increases of aerosols by fuel burning, change in land use, etc.