Environmental Management: Principles and practice

Unstable climate
‘Ice ages’, cold glacial phases alternating with warmer interglacial or less cold
interstadial phases, have happened at several points during the Earth’s history. During
glacials ice extended further from the poles and to lower altitudes on high ground.
The most recent cooling began roughly 40 million BP, became more pronounced
from about 15 million and reached glacial maximum in the last 1.8 to 2.4 million
years (the Quaternary Era). The Quaternary ‘ice age’ has so far comprised over 20
major glacial/ interglacial oscillations. The major interglacials each lasted between
10,000 and 20,000 years and the glacials spanned roughly 120,000 years. The peak
of the last interglacial was about 132,000 to 120,000 BP and the last glacial maximum
was about 18,000 BP. The postglacial seems to have begun quite fast, around 13,000
BP in Europe, and ice had retreated to broadly its present limits world-wide by around
10,000 BP (between 7000 and 3000 BP average conditions may have been as much
as 2°C warmer than today). One might ask whether there is a threat of natural global
cooling and, if so, whether possible anthropogenic warming is such a bad thing?
Many causes have been suggested for natural climatic changes (Broecker and
Denton, 1990; Rudderian and Kutzback, 1991; Paterson, 1993). While their causes

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may be disputed, glacials and interglacials clearly occurred. There are well-established
links between glacial conditions and low levels of carbon dioxide in the atmosphere
(approximately 25 per cent reduction compared with the present), low levels of
methane in the atmosphere, and low sea-levels (which may drop to perhaps 140
metres lower than those of today during glacials). During warm interglacials, carbon
dioxide and methane in the atmosphere were higher than now and sea levels perhaps
40 metres above today’s.
Drought in Africa, the Americas, South East Asia and other parts of the world
and the patterns of monsoonal rainfall have been linked to atmospheric and oceanic
changes which show some periodicity or quasi-periodicity. Particular attention has
focused on the El Niño—Southern Oscillation (ENSO) (and related El Niña events).
ENSO is believed to function in the following manner: a low-pressure, high-
temperature weather system lies over Indonesia; thousands of miles away over the
southwestern Pacific is a related high-pressure, low-temperature system. It has been
established that if pressure in one increases, it falls in the other. These pressure
differences cause the southeast trade winds to blow steadily and move water away
from the western coast of South America. This causes upwelling of nutrient-rich
cold seawater. Every year in spring and autumn there is a weakening, even cessation
of the trade winds, peaking in the middle of the austral summer (around Christmas—
hence El Niño—‘the Boy-Child’) and, if it is fully manifest, the eastern tropical
Pacific can warm markedly (Diaz and Markgraf, 1992). ENSO events cause increased
rain along the Pacific coast of South America and, later, drought in Brazil, Australia
and Australasia and reduced austral summer rainfall and cloud cover in South Africa.
The USA and Central America also feel the effects (Diaz and Markgraf, 1992; Hamlyn,
1992). Study of the phenomenon enabled prediction of recent weather shifts in some
of the aforementioned regions nine months or more in advance.
Infrequent events pose a threat to humankind and it is advisable to devote
resources to providing early warning, defence and mitigation measures.
Environmental management should plan for infrequent as well as more everyday
threats and ongoing processes.