Fw: [CAD] Lessons From Ancient Heat Surge
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November 23, 1999
Lessons From Ancient Heat Surge
By WILLIAM K. STEVENS
What happens when great amounts of heat-trapping greenhouse gases are
injected into the atmosphere in a relatively short span of earth
history, as is happening today as a result of the burning of coal,
oil and natural gas?
One way to help answer this urgent climatic question of the day is to
examine what has happened in similar situations in the remote past.
Now, American and Australian scientists are reporting evidence that
the biggest global warming in the last 100 million years may have
been touched off by a sudden blowout of greenhouse gases from the
The scientists say that for a relatively brief period around 55
million years ago, after the extinction of the dinosaurs but long
before the onset of today's pattern of periodic ice ages, the
temperature of the earth's surface in northern latitudes, and of the
deep ocean, soared by some 9 to 12 degrees Fahrenheit.
This is substantially more than the 5 to 9 degrees the world has
warmed since the depths of the last ice age 18,000 to 20,000 years
So great was the effect of the warming, experts say, that it wiped
out many species of marine life and created climatic conditions that
led to an explosive expansion in the number and variety of mammal
species. It was at this time that the primates, from which Homo
sapiens eventually evolved, first appeared.
The analogy to today's conditions is far from perfect, and many
questions remain to be answered, but those who have investigated the
ancient warming spike say it reinforces a belief that has lately been
growing among climate scientists: that a gradual warming of the
climate can abruptly soar to new heights once a certain threshold is
That is what scientists believe happened in the case of the warming
55 million years ago -- and perhaps what could happen again, in
The chief greenhouse gas was and is carbon dioxide, and since the
start of the Industrial Revolution in the 18th century, its
atmospheric concentration has gradually increased by nearly 30
percent. The average global surface temperature has risen by about 1
degree or a little more in the last century.
Mainstream scientists believe, based on computerized simulations of
the climate's workings, that the temperature will rise by about
another 3.5 degrees by the year 2100 if greenhouse gas emissions
continue at the present rate.
A gradual warming of unknown cause preceded the sharp upward spike in
temperature 55 million years ago, said Miriam E. Katz, a
paleooceanographer at Rutgers University, who is the leading author
of a report on the ancient phenomenon in the current issue of the
But at some point, the warming crossed a threshold that abruptly
kicked the temperature up to a new level, said another author of the
Science paper, Dr. Gerald R. Dickens of James Cook University in
Australia. He compared it to the stretching of a rubber band: "You
gradually pull at both ends and, at some instant, the rubber band
What caused the climate to snap and send the temperature soaring,
according to a hypothesis formulated by Dr. Dickens, was a sudden
release of methane locked in the ocean floor, touched off by the
previous, more gradual warming.
Methane is a greenhouse gas in its own right, and when released from
ocean sediments it also combines with oxygen to form carbon dioxide
that eventually percolates to the atmosphere.
Dr. Dorothy K. Pak of the University of California at Santa Barbara
and Dr. Kenneth G. Miller of Rutgers are the other authors of the
report in Science, which describes chemical and geological evidence
of the ancient rush of greenhouse gases and the way it happened. The
evidence was contained in corings and ultrasound readings of
sediments on a subsea promontory called the Blake Nose, northeast of
Cape Canaveral, Fla.
The researchers believe that the original, gradual warming, beginning
about 60 million years ago, caused a change in ocean circulation
currents that pushed warm surface waters down into the deep sea.
This deep-sea warming converted icelike solid methane locked in
crystalline structures in the sea-floor sediments into gaseous form.
This gas then blasted upward through the sediment, starting mudslides
that freed the methane and allowed it to escape into the water and
eventually to the atmosphere. On the way, it reacted with oxygen to
produce globe-warming carbon dioxide.
One effect of the warming spike, Ms. Katz says, was to transform the
environment of the deep ocean, as evidenced by the extinction of more
than half of all species of microscopic bottom-dwelling animals.
The warming is also believed to have enabled that era's relatively
small array of mammals to spread out into formerly frozen regions to
colonize other continents, where they proliferated in many
Among these were the ancestors of horses, apes and humans.
Dr. Dickens has calculated that the sudden influx of carbon
associated with the sharp spike of global warming 55 million years
ago amounted to at least a billion billion metric tons.
At present rates of carbon-dioxide emission from global sources,
about two-thirds of that amount would be added to the atmosphere by
Some scientists say it is possible that before then, some threshold
could again be surpassed, resulting in an abrupt but unknown change
Many questions remain. The cause of the gradual warming that preceded
the spike 55 million years ago is unknown.
Nor do scientists know the magnitude of the atmospheric
concentrations before the gradual warming trend and the spike,
frustrating comparisons with today. Moreover, it is not clear how
much of the ancient warming resulted from the influx of greenhouse
gas and how much from accompanying changes in ocean circulation; Dr.
Dickens believes both were involved.
A further complication, says Dr. Dickens, is that the influx of
greenhouse gases was spewed initially into the ocean 55 million years
ago, but is going directly into the atmosphere today.
That difference could affect the rate of the consequent warming,
since the ocean's inertia might slow the migration of carbon dioxide
into the air, making the ancient warming spike less abrupt than
The evidence drawn from ocean sediments in the new study was not
fine-grained enough to determine just how sharp the ancient warming
was, Dr. Pak said, though it took place within a few thousand years
Other large, abrupt climatic changes of the more recent past --
during the transition out of the last ice age, for example -- have
taken place within a human lifetime or less and sometimes within a
decade, according to recent evidence.
All of these complications muddy the possible comparison between what
happened in the transformational climatic event 55 million years ago
and what is happening today. Nevertheless, says Dr. Dickens, the
ancient transformation provides a new and continuing opportunity to
explore the possible effects of growing concentrations of greenhouse
gases without resorting to computer-assisted simulations of the
And, he says, it teaches that "the earth can, for natural reasons,
suddenly change dramatically."
Posted by Tim
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