November 30, 2017

QotD: Nuclear winter

Filed under: Environment, Media, Politics, Quotations, Science — Tags: , , , — Nicholas @ 01:00

In 1975, the National Academy of Sciences reported on “Long-Term Worldwide Effects of Multiple Nuclear Weapons Detonations” but the report estimated the effect of dust from nuclear blasts to be relatively minor. In 1979, the Office of Technology Assessment issued a report on “The Effects of Nuclear War” and stated that nuclear war could perhaps produce irreversible adverse consequences on the environment. However, because the scientific processes involved were poorly understood, the report stated it was not possible to estimate the probable magnitude of such damage.

Three years later, in 1982, the Swedish Academy of Sciences commissioned a report entitled “The Atmosphere after a Nuclear War: Twilight at Noon,” which attempted to quantify the effect of smoke from burning forests and cities. The authors speculated that there would be so much smoke that a large cloud over the northern hemisphere would reduce incoming sunlight below the level required for photosynthesis, and that this would last for weeks or even longer.

The following year, five scientists including Richard Turco and Carl Sagan published a paper in Science called “Nuclear Winter: Global Consequences of Multiple Nuclear Explosions.” This was the so-called TTAPS report, which attempted to quantify more rigorously the atmospheric effects, with the added credibility to be gained from an actual computer model of climate. At the heart of the TTAPS undertaking was another equation, never specifically expressed, but one that could be paraphrased as follows:

Ds = Wn Ws Wh Tf Tb Pt Pr Pe etc

(The amount of tropospheric dust = # warheads × size warheads × warhead detonation height × flammability of targets × Target burn duration × Particles entering the Troposphere × Particle reflectivity × Particle endurance, and so on.)

The similarity to the Drake equation is striking. As with the Drake equation, none of the variables can be determined. None at all. The TTAPS study addressed this problem in part by mapping out different wartime scenarios and assigning numbers to some of the variables, but even so, the remaining variables were — and are — simply unknowable. Nobody knows how much smoke will be generated when cities burn, creating particles of what kind, and for how long. No one knows the effect of local weather conditions on the amount of particles that will be injected into the troposphere. No one knows how long the particles will remain in the troposphere. And so on.

And remember, this is only four years after the OTA study concluded that the underlying scientific processes were so poorly known that no estimates could be reliably made. Nevertheless, the TTAPS study not only made those estimates, but concluded they were catastrophic.

According to Sagan and his coworkers, even a limited 5,000 megaton nuclear exchange would cause a global temperature drop of more than 35 degrees Centigrade, and this change would last for three months. The greatest volcanic eruptions that we know of changed world temperatures somewhere between 0.5 and 2 degrees Centigrade. Ice ages changed global temperatures by 10 degrees. Here we have an estimated change three times greater than any ice age. One might expect it to be the subject of some dispute.

But Sagan and his coworkers were prepared, for nuclear winter was from the outset the subject of a well-orchestrated media campaign. The first announcement of nuclear winter appeared in an article by Sagan in the Sunday supplement, Parade. The very next day, a highly-publicized, high-profile conference on the long-term consequences of nuclear war was held in Washington, chaired by Carl Sagan and Paul Ehrlich, the most famous and media-savvy scientists of their generation. Sagan appeared on the Johnny Carson show 40 times. Ehrlich was on 25 times. Following the conference, there were press conferences, meetings with congressmen, and so on. The formal papers in Science came months later.

This is not the way science is done, it is the way products are sold.

Michael Crichton, “Aliens Cause Global Warming”: the Caltech Michelin Lecture, 2003-01-17.

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