William H. Calvin
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copyright ©1998

William H. Calvin
My cover article for the January 1998 issue of The Atlantic Monthly stirred up a lot of discussion, and (as will be seen in my replies that follow) I have benefited considerably from the many suggestions made by readers, reporters, and my friends. The Atlantic's letters column features some of this discussion in both the April and the May 1998 issues. In both cases, I show below the unedited version of my responses. The Atlantic's editing did not always improve things, e.g.,
The physician who waits until "dead certain" is likely to wind up with a dead patient.
appeared in print as
The physician who waits for absolute certainty may wind up with a dead patient.

Here is my reply to the April collection of letters (see The Atlantic's web site for them):
William H. Calvin replies:

I thank the many people who took the time to write. Mr. Arms is concerned about my intervention examples, for how the North Atlantic Current might be stabilized to avoid the slippery slope leading to an abrupt cooling (note, please, that examples are not proposals). I could have easily omitted such easy-to-criticize examples but I needed to convey (using existing technologies that most people already understand) the notion that we actually could do something -- that solutions are likely within reach of our science and technology (and the economy that supports them), that they need not amount to science-fiction terraforming, and that fatalism might well be foolish. Once we spend a decade or two analyzing the heat pump's stability and discovering the beginner's mistakes via computer models, we will likely discover something better than the rain shadows, dams, and ditches which I used to illustrate stabilization possibilities.

Dr. Lalani suggests (as has Gregory Benford in a recent article) some space engineering solutions to overheating. But, as I repeatedly emphasized, gradual warming is not the only way that the Nordic heat pump might fail and trip a catastrophic global cooling. That's why the issue is stabilizing the bistable climate mechanism against all threats, not merely heading off heating. Lalani's final sentence, concerning nuclear blasts, is reckless exaggeration; blowing up ice dams across fjords needs only highway-construction amounts of explosive because the exiting water does the rest of the destruction (that's how dams fail).

Mr. Gildea repeatedly confuses a "warm period" (a temperature-based definition) with an "interglaciation" (a definition based on the lack of ice sheets over Canada and Scandanavia). The best of the ice core records from Greenland (see www.WilliamCalvin.com/climate) show a sharp cooling at about 117,000 years ago, effectively ending the prior warm period, but it took a long time for the ice sheets to return. Note that we can have ice-age-level temperatures without much ice (as happened 122,000 years ago) and we can temporarily have fairly warm temperatures even in the presence of massive ice sheets (as happened 15,000 years ago). Most of the climate flips only last for a few centuries, so ice sheets do not change very much before the temperature flips back.

The temperature flips are our big problem, not the ice; an abupt cooling is like suddenly jacking up a landscape a few thousand feet into a mountainous climatic zone, causing the plants to die and be replaced, first by weeds and then by colder-weather species. For modern humans whose population numbers are dependent on maintaining efficient agriculture, it is the decade-long transition that is so catastrophic (given a slow temperature transition over a 500 year period, we could probably cope). We probably cannot tolerate even a brief flip without civilization toppling.

Mr. Winthrop asserts that climate money would be better spent elsewhere, that we wouldn't have the problem except for overpopulation, and that our ancestors survived prior abrupt coolings. But a sudden reduction in present population (the most likely result of another abrupt cooling) via war, famine, and disease would leave a world of small despotic governments that all hated their neighbors because of genocidal warfare during the crash. We may be able to head that off. Mr. Winthrop may not fear the climate's "ebb and flow" but I certainly do, given how overextended and ignorant we currently are. Hunter-gatherers could move but London can't.

Mr. Boardman confuses the issue of stabilizing abrupt climate change with the increasingly irrelevant debate about whether humans are responsible for the past warming. Abrupt cooling is not the "prediction" that global warming originally was: what I described has happened many times before (every few thousand years), and we now know one way (gradual warming) via which it could happen again. I'm sorry that he denigrates the motives of scientists, because ignorance has traditionally given rise to an expensive and miserable course of action (consider medicine before we understood enough to craft vaccines and antibiotics). We currently do not know what has kept the last 8,000 years free of abrupt flips; we badly need to know, so that we can figure out how to augment the stabilizing mechanisms.

And here is my response to the long letter from six University of Washington atmospheric scientists in the May issue:
William H. Calvin replies:

Just 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 was careful not to "predict" a cooling in the next century). The issue here is managing high-risk situations: how much effort should be expended on a minority possibility, particularly one with a history of having occurred many times in the past? There are many everyday examples of this in medicine, where the physician must often act on incomplete information because of the serious consequences of delay.

A nonmedical analogy 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.

The same focus on the "less likely" is essential in medicine, both in diagnosis and therapy. 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" is likely to 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? Do winds "drive" the oceans or vice versa?) 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, induced by global warming's rainfall and meltwater, 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. One should not confuse advocating stability studies with advocating geoengineering projects (something I was careful to avoid when giving examples of potential interventions).

Climate scientists have not had to cope with managing high-risk situations because, heretofore, 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...."

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