Geoscience Reference
In-Depth Information
to 1.5, 2, 2.5 and 3 of that value would lead to increases of 3-4
°
C, 5-6
°
C, 7-8
°
Cand
8-9
C, respectively (op. cit., 1896, p. 266, table VII).
Part of his motivation for carrying out these very laborious calculations was the
dissatisfaction he felt about contemporary attempts to explain the recent ice ages.
Arrhenius (
1896
, p. 274) was especially scathing about James Croll's astronomical
theory of ice ages (see
Chapter 3
), quoting with approval Luigi de Marchi's conclusion
(translated): 'Now I think I may conclude that from the point of view of climatology
and meteorology, in the present state of these sciences, the hypothesis of Croll seems
to be wholly untenable as well in its principles as in its consequences' (de Marchi,
1895
, p. 166). Arrhenius (
1896
, p. 274) was more inclined to favour de Marchi's view
that a change in atmospheric transparency caused by changes in CO
2
concentration
was a more likely explanation of the global cooling and warming associated with the
ice ages. He had earlier commented that the temperature of the Arctic at an unspecified
time in the Tertiary had been 8-9
°
C warmer than today on the basis of the fossil flora,
and he considered that long-term changes in the atmospheric CO
2
concentration may
have been responsible.
It could be argued that the monitored temperature record from North America and
north-west Europe is flawed because of the urban heat island effect and that the warm-
ing trend evident over the past hundred years is more a function of urbanisation than
of any global trend. One obvious counter-argument is that the synchronous warming
of the oceans has nothing to do with urbanisation. Another is that non-urban areas
show a similar warming trend. Consider, for example, Australia, where more than
90 per cent of the population live in five widely scattered state capital cities (Perth,
Adelaide, Melbourne, Sydney and Brisbane). The many small towns and rural settle-
ments across this vast dry and sparsely inhabited continent all show a warming trend.
In the 100 years between 1910 and 2009, the mean surface temperature across Aus-
tralia increased by 1
°
C (Braganza and Church,
2011
). The decade of 2000-2009 in
Australia was the warmest on record. Most of the continent has become warmer over
the last fifty years, with the lowest rate of warming in the north-west also being associ-
ated with an increase in mean annual precipitation since 1960. These two phenomena
may be related. As a general rule, years of highest rainfall are years of lowest mean
temperature, and vice versa. The greatest warming has been in the spring, and there
has been an increase in the frequency of warm weather, with the number of hot days
per year increasing progressively from 1960 to 2010 (Braganza and Church,
2011
).
Establishing long-term trends in precipitation is not easy, especially in a continent
like Australia, which has the most variable rainfall of any continent or desert region,
particularly in the eastern half of the continent, which is subject to the influence of
ENSO events (Kuhnel et al.,
1990
; Peel et al.,
2002
). There has been a 15 per cent
decrease in winter precipitation in the south-west and south-east of Australia since
the mid-1970s, which is larger than the natural variability. One outcome has been a 60
per cent decline in annual stream flow in the lower Murray-Darling Basin and in the
°
