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Roger Weller, geology instructor

Nuclear Winter
by Fred Slawson
Physical Geology
Fall 2012

Is Nuclear Winter a Possibility?

                Watch any movie or read any book about life after nuclear war and you’re sure to come across the term “nuclear winter”.  The idea is that so much debris will be thrown into the atmosphere as a result of the blasts and resulting fires that it will insulate the Earth from the sun enough to cause a false winter, thereby disrupting what is left of agriculture and making higher latitudes uninhabitable.  The question is, is this good science or is this cold war alarmism?

                In order to answer a question like this analogues are needed.  The species has never tried to cause a nuclear winter so we don’t know outright if we can.  First we must determine the full scale of what thermonuclear total war would look like.  That is, if mankind fired every nuclear weapon in the combined global arsenal what would the resulting destruction likely be?  Not knowing exactly where these weapons are targeted and how many would be intercepted, destroyed before launch, or fail to detonate leaves a bit of a blank spot in the reckoning, so the target scenario is worst case.  The worst case scenario is, if no two bombs thermal bloom areas overlapped and the arsenal was detonated at optimal height.   According to the most recent total world arsenal megatonnage is 8022.  Splitting that up into 6685 1.2 megaton warheads we arrive at a total area affected by the thermal bloom of 1,280,363.04 square miles.  1,280,363.04 square miles is huge but only equals .6% of the total surface of the Earth or 2.2% of the total land area of the earth.  The square of affected land would be as wide as the straight line distance from San Antonio, Texas to Los Angeles, California.

The orange ring shows the combined area of thermal bloom.

                The next thing that must be determined is to try to get an idea of the amount of smoke that would be generated by this event.  Again, we’ve never before ignited 2.2% of the earth’s landmass so we look to history to give us an idea.  In 1997 Indonesia had a fire that engulfed 2890 square miles.  According to this fire in Indonesia released between 0.89 and 2.83 billion tons of CO2.  The theoretical fire is 443.04 times larger than the Indonesia fire so would produce between .394 to 1.25 trillion tons of CO2

                Finally, we must determine what the effect of this particulate matter.  The troposphere at approximately 11 to 12 miles above the surface is the level at which most pollutants and weather effects occur, if the soot and greenhouse gases get above this then they are more likely to have a long lasting negative impact.  We have a case where this has happened, the Mount Tambora explosion in Indonesia which caused global average temperatures to drop between .4 and .7 degrees Celsius across the globe, this doesn’t sound like much but it was enough to cause snowfall in June all the way in New York.  Mount Tambora was estimated at 800 megatons, a 10th of the global arsenal.  They called this “The year without a summer.”  This eruption injected aerosols estimated between 10 million to 120 million tons into the stratosphere, which remained for three years to four years.  It seems like with just this final fact we should be able to create nuclear winter.

Before declaring case closed in favor of nuclear winter, there’s a problem; we’ve never seen more than small traces of smoke and soot from even the biggest fires make it to the stratosphere.  The Spokane Daily Post of 8, August 1945 describes the fires having burned themselves out within several hours despite thoroughly burning an area of 4.1 square miles and there are no reports of the smoke going above thousands of feet.  In the worst instances fires have caused localized temperature changes of a few degrees for a few days but resultant weather effects dissipated the smoke too quickly.  There have been traces detected in the stratosphere from large wildfires but to say that there would be ample material to cause a false winter is a stretch of credibility.  It seems that for now nuclear winter remains outside of man’s capability despite the alarmism.  That’s not to say, however, nuclear winter is impossible, a perfect set of conditions could certainly exist that would allow the ash and smoke of a nuclear detonation to carry above the troposphere and lead to long term climate change.  Likely or not, it is probably best that the species believe that the use of such terrible weapons would vanquish them as surely as their enemies.