# 1.8 End of section questions

## Question 5

Information on the different albedos of various types of surface was given in Section 1.2.1. Given that information:

- (a) Explain how a cover of snow or ice is likely to affect the amount of incident solar radiation absorbed by land or sea.

- (b) According to the TAR, there has been a 20% decrease in global forest area since 1850. If we assume that dark forest cover (with an average albedo of 10 - 20%) has been replaced by farmland and pasture with an albedo similar to that of grassland (say, 35%), why might this have contributed to the radiative forcing of climate over the past 150 years? Would the forcing be positive or negative?

### Answer

- (a) Both snow- or ice-cover on land and sea ice have a very high albedo (up to 90%), and so will reduce the amount of solar radiation absorbed.

- (b) Replacing large areas of dark forest cover with vegetation that reflects ahigher proportion of incident solar radiation effectively increases the planetary albedo; this constitutes a negative radiative forcing. (See Figure 36, Section 2.6.1 for an estimate of the effect this has had.)

## Question 6

One suggested strategy for reducing anthropogenic emissions of methane is to capture the gas generated in landfill sites, and pipe this away for use as a fuel (for local domestic needs, say). But burning methane produces CO2. Why might this still be a sensible option if the overall aim is to reduce the total greenhouse forcing of climate in future?

### Answer

The main point here is that methane is a more powerful greenhouse gas than CO2 (at least on a mass-for-mass basis; Table 2, Section 1.6).

## Question 7

Draw a simple annotated diagram to illustrate the radiative effects (both direct and indirect) of tropospheric sulfate aerosols. Include in your diagram the link with human activities.

### Answer

Something along the lines shown in Figure 21 would be appropriate. Note how a simple annotated diagram like this can communicate a lot of information, much of which would not need to be repeated in detail in the accompanying text (useful if you are working to a tight word limit). Note too that diagrams should always have a caption.

Figure 21 Diagram showing the direct and indirect cooling effects of sulphate aerosols in the lower atmosphere.

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