Notes 75explanation which involve the deep ocean circulation. It is also clear
from paleodata that large changes have occurred at different times in the
past in the formation of deep water and in the deep ocean circulation.
Chapter 3 mentioned the possibility of such changes being induced by
global warming through the growth of greenhouse gas concentrations.
Our perspective regarding the possibilities of future climate change needs
to take into account the rapid climate changes that have occurred in the
past.
Having now in these early chapters set the scene, by describing the
basic science of global warming, the greenhouse gases and their origins
and the current state of knowledge regarding past climates, I move on in
the next chapter to describe how, through computer models of the climate,
predictions can be made about what climate change can be expected in
the future.
Questions
1 Given that the sea level at the end of the last glacial maximum was 120 m
lower than that today, estimate the volume of ice in the ice-sheets that covered
the northern parts of the American and Euroasian continents.
2 How much energy would be required to melt the volume of ice you have
calculated in question 1? Compare this with the extra summer sunshine
north of latitude 60◦which might have been available between 18 000 and
6000 years before the present according to the data in Figure 4.5. Does your
answer support the Milankovitch theory?
3 It is sometimes suggested that the large reserves of fossil fuels on Earth
should bepreserved until the onset ofthe next ice age is closer sothat some
of its impact can be postponed. From what you know of the greenhouse effect
and of the behaviour of carbon dioxide in the atmosphere and the oceans,
consider the influences that human burning of the known reserves of fossil
fuels – see Figure 11.2 – could have on the onset of the next ice age.
Notes for Chapter 4
1 In the IPCC 2001 Report, expressions of certainty such as ‘very likely’ were
related so far as possible to quantitative statement of confidence,virtually
certain(greater than ninety-nine per cent chance that a result is true),very
likely(ninety to ninety-nine per cent chance),likely(sixty-six to ninety per
cent chance),medium likelihood(thirty-three to sixty-six per cent chance),
unlikely(ten to thirty-three per cent chance),very unlikely(one to ten per
cent chance),exceptionally unlikely(less than one per cent chance).
2 Further information in Folland, C. K.et al. (Chapter 2) and Mitchell, J. F. B.
et al. (Chapter 12). In Houghton, J. T., Ding, Y., Griggs, D. J., Noguer, M.,
van der Linden, P. J., Dai, X., Maskell, K., Johnson, C. A. (eds.)Climate
Change 2001: The Scientific Basis. Contribution of Working Group I to