Questions 53cloud formation through the effect of the particles in aircraft emissions.
The overall greenhouse effect of aircraft has been estimated as up to
the equivalent of two or three times the effect of their carbon dioxide
emissions.^18
Details of radiative forcings as projected for the twenty-first century
are presented in Chapter 6 (page 120). Chapters 5 and 6 will explain how
estimates of radiative forcing can be incorporated into computer climate
models so as to predict the climate change that is likely to occur because
of human activities. However, before considering predictions of future
climate change, it is helpful to gain perspective by looking at some of
the climate changes that have occurred in the past.
Questions
1 The lifetime of a carbon dioxide molecule in the atmosphere before it is
exchanged with the ocean is typically less than a year, while the time taken
for an increase in carbon dioxide concentration from fossil fuel burning to
diminish substantially is typically many years. Explain the reasons for this
difference.
2 Estimate how much carbon dioxide you emit each year through breathing.
3 Estimate the size of your share of carbon dioxide emissions from the burning
of fossil fuels.
4 A typical city in the developed world with a population of about one million
produces about half a million tonnes of municipal waste each year. Suppose
the waste is buried in a landfill site where the waste decays producing equal
quantities of carbon dioxide and methane. Making assumptionsabout the
likely carbon content of the waste and the proportion that eventually decays,
estimate the annual production of methane. If all the methane leaks away,
using the information in note 10, compare the greenhouse effect of the carbon
dioxide and methane produced from the landfill site with that of the carbon
dioxide produced if the waste were incinerated instead.
5 A new forest is planted containing a million trees which will mature in forty
years. Estimate the amount of carbon sequestered per year by the forest.
6 Find figures for the amount of fuel used by a typical aircraft and the size of
fleets of the world’s airlines and airforces and estimate the carbon dioxide
emitted globally each year by the world’s aircraft.
7 Search for information about the ozone hole and explain why it occurs mainly
in the Antarctic.
8 What are the main uses of CFCs? Suggest ways in which the emissions of
CFCs to the atmosphere could be reduced more rapidly.
9 Evidence is sometimes presented suggesting that the variations in global av-
erage temperature over the last century or more can all be explained as due
to variations in the energy output of the Sun. There is therefore nothing left
to attribute to the increase in greenhouse gases. What is the fallacy in this
argument?