William H. Calvin, A Brain for All Seasons: Human Evolution and Abrupt Climate Change (University of Chicago Press, 2002). See also http://WilliamCalvin.com/BrainForAllSeasons/49N.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
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William H. Calvin
University of Washington
at the beginning of our warm period, there was mile-high ice here at
the U.S.-Canadian boundary, between Victoria and Vancouver.
That’s because the Puget Lobe was rapidly advancing only
14,000 years ago, triggered by the great episode of rapid global
warming that preceded the Younger Dryas.
When the ice sheet over the Canadian Rockies started to collapse
and spread sideways, the ice came all the way down the Strait of
Georgia. It went past the Strait of Juan de Fuca and on into the
southern part of Puget Sound, covering Seattle’s site up to the
height of a 300-story building. The
local mountains had their own glaciers then, as they still do, but they
didn’t have the major ice sheets capable of filling in between
mountain ranges. It was
the surge from the north that filled up the space between the Cascade
Range to the east and the Olympic Mountains to the west, lasting for
over a thousand years.
A few hundred miles to the east, another such ice advance
blocked a river, creating a great meltwater lake (Lake Missoula) over
northern Idaho and the western part of Montana.
The ice dam broke, of course, with a great outburst flood
surging across the middle of Washington State (we call them the
“scablands” because of the deep channels and plunge pools cut in
the old lava). It must
have been rather loud, too. Temporarily,
the Columbia River had a flow ten times greater than all the rest of
the world’s rivers combined.
The ice dam reformed, and broke again – at least 59 times. Just imagine the biblical flood on fast forward and stuck in
a repeat loop.
We’re descending now, and it’s a little bumpy as we cross
the San Juan Islands. Landing
is always the hard part, and it’s only twenty minutes from now, as I
see the Strait of Juan de Fuca off to the west, stretching out into the
Pacific Ocean. The end of
our warm period isn’t as predictable as the end of an airline flight,
but it, too, surely isn’t far off, if we let nature take its course.
And flip again.
We humans have consciousness in a big way, compared to the great
apes, enabling us to better evaluate risk, danger, and pain.
We pay a big price for it, too:
we can know when we can’t do anything about imminent
But maybe we can do something about it.
our flip-flopping climate is not a simple matter. We need heat
in the right places, such as the Greenland Sea, and not in others right
next door, such as Greenland itself. Man-made global warming is likely
to achieve exactly the opposite – warming Greenland and cooling the
A remarkable amount of specious reasoning is often encountered
whenever we contemplate reducing carbon-dioxide emissions.
It’s not a simple matter of global temperature – I hope
it’s now clear that no simple-minded argument in favor of more
global warming (to “avoid cooling,” or “increase agricultural
productivity”) should be taken seriously.
These clangers are sometimes beginners’ mistakes, but can also
be confuse-the-issue propaganda designed to “buy time” for
That increased quantities of greenhouse gases will lead to
global warming is as solid a scientific prediction as can be found, but
other things influence climate too, and some people try to escape
confronting the consequences of our pumping more and more greenhouse
gases into the atmosphere by supposing that something will come along
miraculously to counteract them. Volcanos
spew sulfates, as do our own smokestacks, and these reflect some
sunlight back into space, particularly over the North Atlantic and
Europe. But we can’t
assume that anything like this will neatly counteract our longer-term
flurry of carbon-dioxide emissions.
Only the most naïve gamblers bet against physics, and only the
most irresponsible bet with their grandchildren’s resources.
To the long list of predicted consequences of global warming –
stronger storms, methane release, habitat changes, ice-sheet melting,
rising seas, stronger El Niños, killer heat waves – we must now add
abrupt, catastrophic coolings. Whereas
the familiar consequences of global warming will simply force expensive
but gradual adjustments, the abrupt cooling and drying promoted by
human-enhanced warming looks like a particularly efficient means of
committing mass suicide.
We cannot avoid trouble by merely cutting down on our present
warming trend, though that’s an excellent place to start.
Paleoclimatic records reveal that any notion we may once have
had that the climate will remain the same unless pollution changes it
is, well, wishful thinking. Judging
from the duration of the last warm period, we are in the declining
centuries of our current one. Our
goal must be to stabilize the climate in its favorable mode and ensure
that enough equatorial heat continues to flow into the waters around
Greenland and Norway. The
stabilized climate must have a wide “comfort zone,” and be able to
survive the El Niños of the short term.
We can design for that in computer models of climate, just as
architects design earthquake-resistant sky scrapers.
Implementing it might cost no more, in relative terms, than
building a medieval cathedral.
Yet we may not have centuries for acquiring wisdom, and it would
be wise to compress our learning into the years immediately ahead.
We have to discover what has made the climate of the past 8,000
years relatively stable, and then figure out how to prop it up.
because great climate flips can happen in response to global
warming doesn’t mean that they are the most probable outcome of our
current situation, what one might “forecast” (that’s one of the
reasons why I’ve been careful not to “predict” a cooling in the
next century). Climate
scientists have a maddening tendency to focus on “the most likely”
outcome in the next century, just as economists and politicians tend to
do, and I believe that is a serious mistake.
The issue here is managing high-risk situations, not the usual
stuff: you can make a lot
of mistakes when you try to extrapolate ‘business as usual.”
How much effort should be expended on a minority possibility,
particularly one with a history of having occurred many times in the
past? Other than military and disaster planners, physicians, and
people in the reinsurance business, not too many people are
knowledgeable about high-risk management.
(I learned some only because my father was an insurance
executive and I later listened to many neurosurgical conferences
discuss the failure of the referring physician to think beyond “the
most likely cause.”)
Guessing the most likely diagnosis and outcome is something that
any second-year medical student can often do.
Even I can do it in some areas like neurology, just from hanging
around real doctors for decades: given
some symptoms and lab findings, I can sometimes say that it’s most
likely disease X. I might
even be right half the time. But
that’s not good enough. The
reason you consult real experts is because they know all the common
mistakes and how to avoid them. And what they do, that the second-year
medical student can’t do yet, is to rule out the less likely
scenarios, particularly the ones that could kill you quickly if left
untreated. Even though
such possibilities are “less likely,” they’re exactly what you
have to focus on.
A homey example would be when you are awakened during the night to hear some strange gurgling noises. The most likely source, you realize as you lie there in bed, is simply a downspout clogged with leaves. Not a serious matter, something that can wait for a sunny weekend. But you also know that the sounds could be coming from a ruptured hose to the washing machine, and you know what a mess a flood can make, in short order. Even though there’s a 80 percent chance of the noise being innocuous, you crawl out of your warm bed and go check things out.
And you see the same focus on the “less likely,” both in
medical diagnosis and therapy, where the physician must often act on
incomplete information because of the serious consequences of delay.
Suppose that with your symptoms and lab findings, the chances
are 80 percent that you’ve got disease X, a nuisance in the long run
but not catastrophic. The
trouble is, the symptoms are also consistent with another more serious
disease, lymphoma, which can quickly kill and needs early treatment.
Even though the chances are only 20 percent that you’ve got
lymphoma, your physician may tell you that you are going to need
chemotherapy “for insurance against cancer.”
You can’t just wait to see what develops.
The possible consequences of delay are simply too great.
The physician who waits until “dead certain” of a diagnosis
before starting treatment may wind up with a dead patient.
That’s our situation with gradual warming and abrupt cooling. It isn’t that abrupt cooling is the most probable outcome
in the next century but that an atmospheric warming from any cause
looks capable of triggering a loss of the warm water loop through the
Labrador and Greenland Seas (the front-runner candidate for what has
caused the observed global abrupt coolings of the past).
One should not get distracted by which-came-first issues (Is the
warming “our fault”?) but focus on consequences – and
particularly the possible consequences of postponing action, of simply
waiting to see what develops. The
failure to flush the cooled-down water from the ocean surface isn’t
even the 20 percent possibility at the moment; it’s the
best-understood candidate for what can trigger global abrupt cooling.
The alternative candidates should not be used to discourage
preventative action on the rapidly-fatal scenario.
Promptly studying how to stabilize the North Atlantic Current
ought to be high on the agenda.
Focusing on “the most likely” outcome is a beginner’s
mistake when the stakes are so high.
Climate scientists have not, heretofore, had to cope with
managing high-risk situations because they’ve had few interventions
to offer. As that changes,
thanks to the magnificent science now being done on climate, they’ll
need some appreciation for how to manage situations described 2,500
years ago by the Hippocratic aphorism, “Life is short, the art long,
opportunity fleeting, experience treacherous, judgment difficult. The physician must be ready . . . .”
boom-and-bust climate cycle shows the challenges that our
ancestors had to contend with. At
the beginning of the ice ages 2.5 million years ago, our ancestors were
walking upright but had ape-sized brains; they were just starting to
make stone tools. By the
time of our most recent ice age, we had a brain three times larger,
capable of making good guesses about what’s likely to happen next,
and often capable of heading off trouble.
But I doubt that another episode of the bust-then-boom climate
will jack us up another notch in brain power.
Ever since agriculture was invented, and transportation
minimized isolation, natural selection has become decoupled from human
evolution, at least the ways it used to operate.
We’re now smart, however, in ways that owe little to our
present brain power, but rather to the accumulated experience of the
people that have lived since the last ice age ended.
We accumulate knowledge and refine wisdom from it.
There’s an element of “use it or lose it” here. Use our civilization’s achievements to prevent the next whiplash, or lose much of civilization’s gains as our warm period suddenly ends with a population crash.
On to the
Afterthoughts and Acknowledgements
Copyright ©2002 by
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Calvin Home Page
All of my books are on the web. The six out-of-print books
are again available via Authors Guild reprint editions,
All of my books are on the web.
The six out-of-print books
are again available via Authors Guild reprint editions,