THE THREAT OF CLIMATE CHANGE (George Monbiot, 2003)
SHADOW OF EXTINCTION
degrees separate our world from the cataclysmic end of an ancient era.
The Guardian, Tuesday July 1, 2003,
It is old news, I admit. Two hundred and fifty-one million years old, to be
precise. But the story of what happened then, which has now been told for the
first time, demands our urgent attention. Its implications are more profound
than anything taking place in Iraq, or Washington, or even (and I am sorry to
burst your bubble) Wimbledon. Unless we understand what happened, and act upon
that intelligence, prehistory may very soon repeat itself, not as tragedy, but
The events that brought the Permian period (between 286m and
251m years ago) to an end could not be clearly determined until the mapping of
the key geological sequences had been completed. Until recently,
palaeontologists had assumed that the changes that took place then were gradual
and piecemeal. But three years ago a precise date for the end of the period was
established, which enabled geologists to draw direct comparisons between the
rocks laid down at that time in different parts of the world.
Having done so, they made a shattering discovery. In China,
South Africa, Australia, Greenland, Russia and Svalbard, the rocks record an
almost identical sequence of events, taking place not gradually, but relatively
instantaneously. They show that a cataclysm caused by natural processes almost
brought life on earth to an end. They also suggest that a set of human
activities that threatens to replicate those processes could exert the same
effect, within the lifetimes of some of those who are on earth today.
As the professor of palaeontology Michael Benton records in
his new book, When Life Nearly Died, the marine sediments deposited at the end
of the Permian period record two sudden changes. The first is that the red or
green or grey rock laid down in the presence of oxygen is suddenly replaced by
black muds of the kind deposited when oxygen is absent. At the same time, an
instant shift in the ratio of the isotopes (alternative forms) of carbon within
the rocks suggests a spectacular change in the concentration of atmospheric
On land, another dramatic transition has been dated to
precisely the same time. In Russia and South Africa, gently deposited mudstones
and limestones suddenly give way to massive dumps of pebbles and boulders. But
the geological changes are minor in comparison with what happened to the animals
The Permian was one of the most biologically diverse periods
in the earth's history. Herbivorous reptiles the size of rhinos were hunted
through forests of tree ferns and flowering trees by sabre-toothed predators. At
sea, massive coral reefs accumulated, among which lived great sharks, fish of
all kinds and hundreds of species of shell creatures.
Then suddenly there is almost nothing. The fossil record very
nearly stops dead. The reefs die instantly, and do not reappear on earth for 10
million years. All the large and medium-sized sharks disappear, most of the
shell species, and even the great majority of the toughest and most numerous
organisms in the sea, the plankton. Among many classes of marine animals, the
only survivors were those adapted to the near-absence of oxygen.
On land, the shift was even more severe. Plant life was
almost eliminated from the earth's surface. The four-footed animals, the
category to which humans belong, were nearly exterminated: so far only two
fossil reptile species have been found anywhere on earth that survived the end
of the Permian. The world's surface came to be dominated by just one of these,
an animal a bit like a pig. It became ubiquitous because nothing else was left
to compete with it or to prey upon it.
Altogether, Benton shows, some 90% of the earth's species
appear to have been wiped out: this represents by far the gravest of the mass
extinctions. The world's "productivity" (the total mass of biological matter)
Ecosystems recovered very slowly. No coral reefs have been
found anywhere on earth in the rocks laid down over the following 10 million
years. One hundred and fifty million years elapsed before the world once again
became as biodiverse as in the Permian.
So what happened? Some scientists have argued that the mass
extinction was caused by a meteorite. But the evidence they put forward has been
undermined by further studies. There is a more persuasive case for a different
explanation. For many years, geologists have been aware that at some point
during or after the Permian there was a series of gigantic volcanic eruptions in
Siberia. The lava was dated properly for the first time in the early 1990s. We
now know that the principal explosions took place 251 million years ago,
precisely at the point at which life was almost extinguished.
The volcanoes produced two gases: sulphur dioxide and carbon
dioxide. The sulphur and other effusions caused acid rain, but would have bled
from the atmosphere quite quickly. The carbon dioxide, on the other hand, would
have persisted. By enhancing the greenhouse effect, it appears to have warmed
the world sufficiently to have destabilised the superconcentrated frozen gas
called methane hydrate, locked in sediments around the polar seas. The release
of methane into the atmosphere explains the sudden shift in carbon isotopes.
Methane is an even more powerful greenhouse gas than carbon
dioxide. The result of its release was runaway global warming: a rise in
temperature led to changes that raised the temperature further, and so on. The
warming appears, alongside the acid rain, to have killed the plants. Starvation
then killed the animals.
Global warming also seems to explain the geological changes.
If the temperature of the surface waters near the poles increases, the
circulation of marine currents slows down, which means that the ocean floor is
deprived of oxygen. As the plants on land died, their roots would cease to hold
together the soil and loose rock, with the result that erosion rates would have
So how much warming took place? A sharp change in the ratio
of the isotopes of oxygen permits us to reply with some precision: 6C. Benton
does not make the obvious point, but another author, the climate change
specialist Mark Lynas, does. Six degrees is the upper estimate produced by the
UN's scientific body, the intergovernmental panel on climate change (IPCC), for
global warming by 2100. A conference of some of the world's leading atmospheric
scientists in Berlin last month concluded that the IPCC's model may have
underestimated the problem: the upper limit, they now suggest, should range
between 7 and 10 degrees. Neither model takes into account the possibility of a
partial melting of the methane hydrate still present in vast quantities around
the fringes of the polar seas.
Suddenly, the events of a quarter of a billion years ago
begin to look very topical indeed. One of the possible endings of the human
story has already been told. Our principal political effort must now be to
ensure that it does not become set in stone.