Nuclear Weapons in a Changing Climate – vitu chele
Many people tend to think that the outcome of any nuclear weapons use today will result in an escalatory situation with apocalyptic outcomes for the countries involved.1 Yet many factors are increasing the probability of the limited use of nuclear weapons (e.g., 1 to 20 warheads) in a range of conflict scenarios. Previous atmospheric model simulations of regional nuclear conflicts employing many relatively small bombs have been estimated to cause a global “nuclear autumn,” with great reductions in agricultural productivity, stratospheric ozone loss, and spread of hazardous radioactive fallout.
The totality of these effects would result in widespread damage to human well-being and to terrestrial and aquatic ecosystems. In this article, we estimate minimum thresholds for the prevalent types of currently deployed nuclear weapons that would cause equivalent climate impacts, and provide a discussion of the factors that may influence the probability of nuclear weapons use, current risk perception, and possible mitigation actions.
A reasonable estimate indicates that the total energy released by nuclear explosions in the twentieth century amounts to six hundred megatons TNT equivalent of energy, or 2.5 billion, billion Joules (2.5 x 1018 J). Divided over the five hundred and ten million, million square meters of the Earth’s surface (510 x 1012 m²), and over the two decades of peak testing, that represents eight millionth of a Watt per square meter (8 x 10–6 W m-2) of power. For comparison, the 1.8 Watts per square meter (1.8 W m-2) of CO2 radiative forcing as of 2011 generates approximately twenty nine billion, trillion Joules of energy (29 x 1021 J) over the Earth’s surface in a single year, or more than ten thousand times as much energy in a year that the entire combined nuclear weapons program of the world has generated.
That is not the whole story. Many nuclear tests kick up a lot of dust, which reflects sunlight, thereby cooling the Earth. Indeed, according to Turco et al, 1983, that is the dominant effect of nuclear explosions on climate. The result is that nuclear testing is likely to have reflected more energy from the Sun than they generated. That is, nuclear testing is likely to have been a net cooling factor.
In the 1980s and early 1990s, a series of scientific papers published by Soviet scientists and Western scientists laid out the dire consequences on global climate of a major nuclear exchange between the U.S. and Soviet Union. The nuclear explosions would send massive clouds of dust high into the stratosphere, blocking so much sunlight that a nuclear winter would result. Global temperatures would plunge 20°C to 40°C for several months, and remain 2–6°C lower for 1–3 years. Up to 70% of the Earth’s protective stratospheric ozone layer would be destroyed, allowing huge doses of ultraviolet light to reach the surface.
This UV light would kill much of the marine life that forms the basis of the food chain, resulting in the collapse many fisheries and the starvation of the people and animals that depend it. The UV light would also blind huge numbers of animals, who would then wander sightlessly and starve. The cold and dust would create widespread crop failures and global famine, killing billions of people who did not die in the nuclear explosions. The “nuclear winter” papers were widely credited with helping lead to the nuclear arms reduction treaties of the 1990s, as it was clear that we risked catastrophic global climate change in the event of a full-scale nuclear war.
Well, it turns out that this portrayal of nuclear winter was overly optimistic, according to a series of papers published over the past few years by Brian Toon of the University of Colorado, Alan Robock of Rutgers University, and Rich Turco of UCLA. Their most recent paper, a December 2008 study titled, “Environmental Consequences of Nuclear War”, concludes that “1980s predictions of nuclear winter effects were, if anything, underestimates”. Furthermore, they assert that even a limited nuclear war poses a significant threat to Earth’s climate.
The scientists used a sophisticated atmospheric/oceanic climate model that had a good track record simulating the cooling effects of past major volcanic eruptions, such as the Philippines’ Mt. Pinatubo in 1991. The scientists injected five terragrams (Tg) of soot particles into the model atmosphere over Pakistan in May of 2006. This amount of smoke, they argued, would be the likely result of the cities burned up by a limited nuclear war involving 100 Hiroshima-sized bombs in the region. India and Pakistan are thought to have 109 to 172 nuclear weapons of unknown yield.
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