Book review.
Have
humans forestalled an Ice Age?
By Anthony
Toole
Plows,
Plagues and Petroleum.
By William
F. Ruddiman
Princeton
University Press
202 pages;
£15.95
ISBN 0 691
12164 8
Few serious scientists doubt that the
Industrial Revolution has led to one of the 21st Century’s most
intractable problems, global warming. Almost daily we are bombarded with
prognostications of doom should we fail to curb our prodigal use of fossil
fuels and our consequent emission of the greenhouse gases, carbon dioxide and
methane. In this well-argued book, subtitled ‘How Humans Took Control of
Climate’, the author, retired Professor of Environmental Sciences at the
University of Virginia, goes much farther. He puts forward the hypothesis that
global warming is not a new phenomenon, but has been proceeding for the past
8000 years, since humans abandoned a hunter-gatherer lifestyle in favour of
agriculture and a settled existence.
As evidence, he gathers data accumulated
over the past fifty years by scientists studying subjects as diverse as ancient
pollen grains, marine plankton, sea temperature and salinity, tree rings, coral
growth and cores from lake sediments and polar ice. These tell of a series of
up to fifty Ice Age cycles during the last 275 million years, all correlating
with fluctuations in atmospheric concentrations of the primary greenhouse
gases. The driving forces for these cycles have been in the regular and
predictable periodic shifts in the tilt of the Earth’s axis and variations in
the shape of Earth’s orbit around the sun.
For the past eleven thousand years, we
have been in that part of an interglacial cycle in which the carbon dioxide
concentration and the temperature of the Earth should have been expected to
show a steady fall. The data indicate that since around 6000 BC, both of these
figures have been rising. The change in direction coincides with the spread of
agriculture and the accompanying slash-and-burn destruction of the forests, the
world’s great carbon reservoirs. The evidence also shows that the start of
large-scale irrigation and the cultivation of rice occur at the same time as
the rise in the concentration of methane. This even more potent greenhouse gas
is a product both of wetland agriculture and the guts of domesticated farm
animals.
Ruddiman accepts that his hypothesis is
just that, and needs more research if it is to be accepted as theory, but his
arguments are very persuasive. He is able to link anomalous falls in carbon
dioxide concentrations during the past 2000 years with major pandemics that
wiped out huge numbers of people and allowed forests to regain some short-lived
measure of climate control. He suggests that this slow but inexorable warming
has forestalled the Ice Age in the grip of which we should now be living.
The book is concise, very well written and
free of scientific jargon. The arguments are clearly presented, and supported
by graphs that are easy to understand.
In the final section, Ruddiman departs
from pure science and allows the expression of his own opinions. He is critical
of extreme representatives of both viewpoints: the environmentalists who
exaggerate alarmingly, and the industrialists who deny that global warming is a
problem or even exists. Both extremes are selective in the evidence they
present, and this leads to confusion among the public. It is the latter
viewpoint that comes in for the more withering criticism.
Global warming is a fact, and a problem
that will not go away, though Ruddiman suggests that the not unrelated
depletion of the Earth’s natural resources may prove to be a bigger problem. On
the whole, he comes down in favour of a technological solution rather than
Kyoto. The book, however, presents a plea for a coherent and balanced debate.
Anyone wishing to take part seriously in this debate could do no better than
start here.