A recent issue of Nature (19 May 2011, p. 275-276) discusses Nuclear Winter. Many people may recall that in the 1970's about 70,000 nuclear weapons were pointed at various nations in a condition aptly named Mutually Assured Destruction, or MAD.
Translation: you pop me, and I’ll obliterate all your cities within 20 minutes.
Atmospheric and nuclear physicists, among a large number of other worried people all over the world, published several papers pointing out that the soot raised by a MAD nuclear exchange would lead to a massive drop in world temperatures. Bottom line: those who die in the initial detonations would be the lucky ones. The rest of the human population would slowly freeze and starve to death. As a child, this possibility preoccupied me a lot.
There is a precedent for this, by the way. About 74,000 years ago there was a supervolcano eruption (Toba volcano) in Indonesia that, according to scientists analyzing genetic diversity, triggered a freeze that reduced the human population worldwide to as few as 2,000 people - creating a bottleneck in human evolution.
Because of these studies, Mikhail Gorbachev took steps in parallel with Ronald Reagan to reduce the tension in the 1980's, as well as to reduce the world-wide arsenal. Today there are about 22,000 nuclear weapons in the world, and with the New Start Treaty this could drop to 5,000.
The authors of the Nature paper point out that at least 200 known (if unacknowledged) ballistic nuclear weapons in Israel, a rapidly-growing arsenal in increasingly-unstable Pakistan, unknown arsenals in India and China, and an imminent nuclear arsenal in increasingly bellicose Iran, all pose a growing and very real threat to humanity as a whole.
Human history has a consistent and bad track record of one charismatic nut causing the deaths of up to 20,000,000 people at a time - Stalin’s collectivization and Hitler’s Aryan War come to mind.
The Nature authors have access to far better atmospheric models than were available just a decade ago. These models can deal with more variables, have a far finer 3-D modeling grid, and all of the modeling is based on much better experimental data. Here’s what the modeling now tells us:
Their initial assumption is a 50 Hiroshima-bomb equivalent nuclear exchange - say between Pakistan and India, but Iran-Israel is another real possibility. If lobbed at cities, the soot raised by these detonations will amount to a calculated 5 megatons of smoke and soot raised. Open-air tests in the 1960's show that this debris will quickly reach the Troposphere, and new models show it will be heated and rise to the Stratosphere, where it will circulate worldwide for years.
There’s no safe hidey-hole, either: an exchange in the Northern Hemisphere will take awhile, but WILL reach and impact the Southern Hemisphere.
50 Hiroshima bombs will drop the worldwide average temperature by -0.7 degrees C. This sure doesn’t sound like much, but it is comparable to the temperature drop during the Little Ice Age (~1500AD - 1850AD). During this time, millions died of famine in Europe alone.
An even larger exchange is a real possibility - and carries with it proportionally greater consequences. The modeling is not advanced enough to even know if the increase will in fact be proportional - it could push the Earth’s climate to a tipping-point where a new Glacial Age is precipitated. We know just enough to be scared, and this clearly comes across in the dry scientific discussion of the Nature article.
The underlying problem right now is that the human population is huge (over 6 billion and growing) and meta-stable. By meta-stable, I mean that a small perturbation (as a physicist would say it) may have huge, DIS-proportionate consequences. There are vast numbers of people living right on the edge of survivability - seeking food on a day-to-day basis. There are already huge famines underway in North Korea and East Africa.
What can YOU do about this? As an individual, not much, beyond gathering a years supply of food and water. Why would you bother? Because you may be able to help neighbors on your block and in east Africa when (not if) the worldwide food situation worsens.
This is a basic responsibility for anyone who calls themselves followers of Christ.
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