Present climate and biological change - Climate Change: Biological and Human Aspects - page 219

year 1941 also saw a harsh winter, as did 1942, but there were successively fewer
pneumonia and bronchitis cases as the most vulnerable had already died (Burroughs,
1997). This last point is also relevant to longer-term climatic change over a number
of years compared to the impact of an isolated atypical year.
Returning to the question of food and the security of supply, one famine is par-
ticularly notorious in the 19th century: the Irish potato famine. This famine of 1845
was caused by the potato blight fungus, Phytophthora infestans . The climate of the
autumns of 1845 and 1846 was particularly conducive to its spread. However, that
a million Irish peasants died (and another million and a half emigrated as a result)
cannot solely be laid at climate's door. Little then was known about such fungi, let
alone their life cycle and habitat preferences: these were to be later elucidated by the
German biologist Anton de Bary. The use of monocultures, the few potato cultivars
(strains) available, the high population density as supported by near-subsistence farm-
ing (living on the edge) and a virulent new strain of the pathogen, together with the
weather, all combined synergistically to aggravate the famine. As with climate and
seasonal mortality, there are parallels with the position in which we find ourselves
today. True, today the developed nations are not dependent on subsistence farming,
but this just means that the ante has been upped: we have today a far higher population
(more than 7 billion in 2012 and more than 6 billion at the end of the 20th century
as opposed to fewer than 2 billion at its beginning) that is supported by globally
connected, intensive agricultural systems. Today we are reliant on a slightly broader
base of crop cultivars, but the conservation of genetic strains and wildlife biodiversity
(the source of new natural genetic material) are still problematic. We are still close
to the edge; possibly too close? As we shall see, climate change and weather can still
serve to aggravate agricultural problems in the 21st century.
The Little Ice Age ended towards the end of the 19th century and the global climate
began to warm by around half a degree Celsius towards roughly the millennial average
( 1000-2000). This was followed by a 50-year period of stability. Computer models,

both including and excluding the human addition of greenhouse gases, suggest that
the Little Ice Age would have ended as it did through to the mid-20th century, but that
the longer-term trend from the middle of the 20th century would have been one of
gradual cooling to broadly somewhere around

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0.2 ◦ C of what was in reality the

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1961-90 mean had not anthropogenic greenhouse gases been added (see IPCC, 2007,
chapter 9). As it was, not only did the Little Ice Age end, but additional warming
took place in the latter third of the 20th century. Figure 5.4 shows the actual 3-year-
smoothed global temperature change since 1850 relative to the 1961-90 average as
determined by systemised meteorological recording.
Looking at the recent year-by-year global climate as is directly measured (as
opposed to the earlier longer-term climate changes inferred by all the various climate
proxies), is what causes the shorter-term drunkard's walk of climate change. Since the
beginning of chapter 3 we have explained the major shifts in climate as the biosphere
has developed, switched between modes, and been subject to sudden vagaries such as
the carbon isotope excursion (CIE) or volcanic events. But, for example, given that
there were no major eruptions or the like in the period 2000-9, and given we were still
pumping greenhouse gases into the atmosphere, why did global warming halt and

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