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Monday, July 21, 2014

Nuclear Winter? Again? Really?

This may be showing my age, but I remember the storm of media coverage of "nuclear winter" in the 1980's--a theory that a nuclear war would freeze the planet. Although not an author of the research paper, Carl Sagan prominently supported the conclusion. However, the theory was discredited because the researchers had made too many assumptions and short cuts to get their model to work, including getting rid of pesky things like day/night cycles, seasons, geographic features, and so on.

Today I saw in the Daily Mail another group of scientists pushing "nuclear winter." From the article:
The unnerving consequences were laid out in a paper called ‘Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict.’

In it the researchers looked at the outcome of a ‘limited, regional nuclear war between India and Pakistan in which each side detonates 50 15-kiloton weapons.’
 
They then used computer models to examine the impact on the planet and its environment - and it makes for grim reading. 
The immediate result of 100 nuclear weapons roughly the size of those dropped on Hiroshima and Nagasaki being detonated would be the release of five megatons of black carbon into the atmosphere. 
Black carbon, not too dissimilar to soot, would block out the sun and can also be fatal to humans. 
Following a spell of black carbon rain, a deadly weather front that would devastate what remained of humanity following the nuclear war, the temperature of Earth would begin to drop. 
After a year the temperature would fall by 1°C (2°F), while after five it would be 1.5°C (3°F) cooler than it is now. 
About 20 years after the conflict it would warm again to just 0.5°C (1°F) below today’s temperature. 
Accompanying what the researchers call ‘the coldest average surface temperatures in the last 1,000 years’ would be a huge loss in ozone levels. 
They say that global ozone losses of 20 to 50 per cent would occur over populated areas, ‘levels unprecedented in human history’.

The drop in temperature would produce ‘killing frosts’ that reduce the world’s growing season by 10 to 40 days.
 
Meanwhile the eradication of up to half of the ozone would increase UV rays in some locations by as much as 80 per cent, raising the chance of developing skin cancer for large swathes of humanity. 
Combined with the global cooling, this ‘would put significant pressures on global food supplies and could trigger a global nuclear famine.’ 
The planet’s falling temperature would also decrease the amount of rainfall.
The article indicates that the scientists hope their paper will encourage countries to reduce or eliminate nuclear weapons from their arsenals.

Considering the political stance of the scientist involved, and inability of climate scientists to successfully model global climate with any accuracy, I have serious doubts about the conclusion offered up by these scientists. However, I'm even more skeptical when I consider that we had several times the number and power of nuclear weapons tests in the late 1950's and early 1960's without the consequences predicted in the paper. (1958 alone had over a 100 tests conducted, while 1962 had approximately 140 tests--and these were generally much more powerful weapons). Many of these weapons were much more powerful than the bombs used in the paper's hypothetical war. For instance, the paper assumes a war using 100 weapons of the size used on Hiroshima and Nagasaki. The yields varied, but we will assume 20 kT as an average, for a total yield of 2 MT for their hypothetical war. The Tsar Bomb--a single nuclear test conducted by the Soviet Union in 1961--had a yield of nearly 60 MT. That is, three times the total power of the weapons in the hypothetical war. And it was only one of many tests that year.

In other words, if more above-ground tests using more powerful weapons did not result in a global nuclear winter in the 1950's and 1960's, I'm pretty sure that it wouldn't happen with the more limited war envisioned by the scientists in the Daily Mail article.

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