Aftermath of a Hypothetical Nuclear War

At the height of the Cold War, scientists began modelling the after effects of a nuclear war between the United States and the Soviet Union. The results proved that the world was fortunate that such a war never happened. They showed the Earth cooling, in what became termed ‘nuclear winter’, paired with a depletion of the ozone layer that produced an ‘ultraviolet spring’. The Soviet Union and United States reduced their number of warheads, but today there are nine nations known to have a combined force of nearly 16,000 nuclear warheads.
Scientists have since run updated models to simulate a nuclear war, and the effects were even more intense than previous predictions, as the new models could take into account more details of the complicated systems involved. A nuclear warhead of 15 kilotons (kt), such as the one used on Hiroshima, would create devastating firestorms and destruction in modern cities. That brings us to today’s article, “Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict” by Michael J. Mills, Owen B. Toon, Julia Lee-Taylor, and Alan Robock. The article appeared in an American Geophysical Union publication known as Earth’s Future in 2014.
This article discussed the modelling of a nuclear war more typical of post Cold War simulations; fifty 15 kt nuclear warheads detonated by both India and Pakistan. The model used here is a more complete model than has been used before, combining the effects of the ocean, land, sea ice, and atmosphere. The simulation was run to model the time frame of January 1st, 2013 to January 1st, 2039. It was also run starting at May 15th, but the difference in season made no significant difference in the results. The simulation modeled the production of black carbon, in this case from fine soil smoke from the explosions.  In this case, it was 5 Teragrams of black carbon–tera being 1012. This somewhat unimaginable amount of black carbon had profound effects on the Earth.
Between 1.2 and 1.6 Teragrams of the black carbon falls out of the atmosphere through rainout within the first four months. The remaining black carbon will slowly remove itself naturally from the atmosphere, but around a Teragram still exists in the atmosphere a decade after the war.
The average global surface temperature drops by about 1.1 Kelvin (1.1 C, or about 2 F) in the first year; the cooling continues to 1.6 K (2.66 F) in the fifth year. The temperature is still down by 1.1 K (2 F) ten years later. The temperatures remain 0.25 to 0.5 K (.45 to .9 F) below the control in years 20 to 23.
Average over the globe, precipitation rates drop by 6% or 0.18 millimeters per day (0.007 inches per day) for the first year. This continues for the first five years, and then it drops further, 9% compared to the control simulations (0.27 millimeters/day, or 0.1 inches/day). Ten years later, this is still down by 4.5% (0.135 millimeters/day, or 0.005 inches/day). This may not sound like much, but the effects could be dramatic, as discussed later.
At the end of the simulation, 26 years after the fictional war, both precipitation and temperature are below the control model’s prediction.
At the poles, sea ice is extending. It extends for the first five years in the Arctic, and the first ten years at the Antarctic. The sea ice begins extending earlier in autumn for both hemispheres. In years 4 to 7 after the war, the Arctic is 10-25% above control, and the Antarctic spends years 7 to 15 at 20-75% above, and years 20 to 26 at 5-10% above the control models. This affects the oceans, the atmosphere, and albedo. Albedo is a measure of how much sunlight is absorbed into the Earth’s system. More ice will increase albedo, reflecting more sunlight, and furthering the cooling discussed previously.
As far as the ocean is concerned, its global average temperature is down by over 0.5 K (0.9 F) 100 meters (328 feet) deep, for twelve years. At depths of 1000 meters (0.6 miles), the temperature continues to drop for all 26 years contained in the model.
The atmosphere is also affected. Black carbon cools the surface, yet heats up part of the atmosphere. The stratosphere goes up 80 K (144 F), and over 30 K (54 F) for the first five years. This has a startling effect on the ozone layer, depleting it on a global average 20-25%. This is a combination of 30-40% in the midlatitudes, 50-60 in the northern high latitudes. The effect is from chemical reactions involving oxygen and nitrogen, which quicken in warmer temperatures. Since most of the ozone is produced in the tropics, the areas further away have a greater drop, the chemical affects accumulating. High southern latitudes do not see such a drastic drop compared to the control as this area already has a seasonal hole in the ozone layer.
A diagram of Earth's atmospheric levels. Taken from Portrait of a Planet, page 699.
A diagram of Earth’s atmospheric levels. Taken from Portrait of a Planet, page 699.
The reason we care about the ozone layer is because it shields us from the sun’s harmful UV radiation. It is measured by the UV Index. This generally goes from 0 to 11, with 11 being considered ‘extreme’. The models show UV Index levels 3 to 6 levels higher than what would otherwise be expected. Over many parts of the world, levels reach 12 to 21 in summertime, well off the usual scale.
The combination of more UV radiation, cooler temperatures, and less precipitation make for rather unhappy plants. For years two through six, the growing season is shortened by 40 days. Larger, prolonged doses of UV radiation also effect plants, generally reducing them in size, along with other effects, such as changing how resistant they are to insect attacks.
Ozone depletion also affects aquatic life. At 16% ozone depletion, phytoplankton could reduce by 5%; this works its way up the aquatic food chain to result in 7 million tons less fish every year.  Between the change in aquatic life and plants, the food supply for humans could be drastically affected. The authors use a term I haven’t seen before: “global nuclear famine”. Political reaction likely would exacerbate any issue that arises in the food supply, and it would be politics that started all of this in the first place.
As devastating as wars are, a nuclear war would be much worse–not just for the countries involved, their soldiers and civilians, but for the entire planet.

 

 

Bibliography
Mills, Michael J., et al. “Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict.” Earth’s Future 2.4 (2014): 161-176.
Today’s main article.
Stephen Marshak. Earth: Portrait of a Planet. Third Edition. New York: W. W. Norton & Company, 2007. Print.
My geology textbook, used for the diagram of the atmosphere.
Stockholm International Peace Research Institute. “World Nuclear Forces.” Page. N.p., n.d. Web.
An informative page used for information on the current state of nuclear warheads in the world.
United States Environmental Protection Agency. “Black Carbon: Basic Information.” Overviews & Factsheets. N.p., n.d. Web.
A page about the basics of black carbon.
United States Environmental Protection Agency.  “UV Index Scale.” Overviews and Factsheets. N.p., n.d. Web.
A page explaining the UV Index.
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