Nuclear winter

Nuclear winter is a severe and prolonged global climatic cooling effect hypothesized to occur after widespread firestorms following a nuclear war. The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine. When developing computer models of nuclear-winter scenarios, researchers use the conventional bombing of Hamburg, and the Hiroshima firestorm in World War II as example cases where soot might have been injected into the stratosphere, alongside modern observations of natural, large-area wildfire-firestorms.Stenchikov et al. conducted detailed, high-resolution smoke plume simulations with the RAMS regional climate model and showed that individual plumes, such as those from the Kuwait oil fires in 1991, would not be expected to loft into the upper atmosphere or stratosphere, because they become diluted. However, much larger plumes, such as would be generated by city fires, produce large, undiluted mass motion that results in smoke lofting. New large eddy simulation model results at much higher resolution also give similar lofting to our results, and no small scale response that would inhibit the lofting .A global average surface cooling of −7 °C to −8 °C persists for years, and after a decade the cooling is still −4 °C (Fig. 2). Considering that the global average cooling at the depth of the last ice age 18,000 yr ago was about −5 °C, this would be a climate change unprecedented in speed and amplitude in the history of the human race. The temperature changes are largest over land … Cooling of more than −20 °C occurs over large areas of North America and of more than −30 °C over much of Eurasia, including all agricultural regions.global ozone losses of 20–50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30–80% over Mid-Latitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10–40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years, due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine.As the science progressed and more authentic sophistication was achieved in newer and more elegant models, the postulated effects headed downhill. By 1986, these worst-case effects had melted down from a year of arctic darkness to warmer temperatures than the cool months in Palm Beach! A new paradigm of broken clouds and cool spots had emerged. The once global hard frost had retreated back to the northern tundra. Mr. Sagan's elaborate conjecture had fallen prey to Murphy's lesser-known Second Law: If everything MUST go wrong, don't bet on it. Nuclear winter is a severe and prolonged global climatic cooling effect hypothesized to occur after widespread firestorms following a nuclear war. The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine. When developing computer models of nuclear-winter scenarios, researchers use the conventional bombing of Hamburg, and the Hiroshima firestorm in World War II as example cases where soot might have been injected into the stratosphere, alongside modern observations of natural, large-area wildfire-firestorms. 'Nuclear winter,' or as it was initially termed, 'nuclear twilight,' began to be considered as a scientific concept in the 1980s, after it became clear that an earlier hypothesis, that fireball generated NOx emissions would devastate the ozone layer, was losing credibility. It was within this context that the climatic effects of soot from fires became the new focus of the climatic effects of nuclear war. In these model scenarios, various soot clouds containing uncertain quantities of soot were assumed to form over cities, oil refineries, and more rural missile silos. Once the quantity of soot is decided upon by the researchers, the climate effects of these soot clouds are then modeled. The term 'nuclear winter' was a neologism coined in 1983 by Richard P. Turco in reference to a 1-dimensional computer model created to examine the 'nuclear twilight' idea, this 1-D model output the finding that massive quantities of soot and smoke would remain aloft in the air for on the order of years, causing a severe planet-wide drop in temperature. Turco would later distance himself from these extreme 1-D conclusions. After the failure of the predictions on the effects of the 1991 Kuwait oil fires, that were made by the primary team of climatologists that advocate the hypothesis, over a decade passed without any new published papers on the topic. More recently, the same team of prominent modellers from the 1980s have begun again to publish the outputs of computer models, these newer models produce the same general findings as their old ones, that the ignition of 100 firestorms, each comparable in intensity to that observed in Hiroshima in 1945, could produce a 'small' nuclear winter. These firestorms would result in the injection of soot (specifically black carbon) into the Earth's stratosphere, producing an anti-greenhouse effect that would lower the Earth's surface temperature. The severity of this cooling in Alan Robock's model suggests that the cumulative products of 100 of these firestorms could cool the global climate by approximately 1 °C (1.8 °F), largely eliminating the magnitude of anthropogenic global warming for the next roughly two or three years. Robock has not modeled this, but has speculated that it would have global agricultural losses as a consequence. As nuclear devices need not be detonated to ignite a firestorm, the term 'nuclear winter' is something of a misnomer. The majority of papers published on the subject state that without qualitative justification, nuclear explosions are the cause of the modeled firestorm effects. The only phenomenon that is modeled by computer in the nuclear winter papers is the climate forcing agent of firestorm-soot, a product which can be ignited and formed by a myriad of means. Although rarely discussed, the proponents of the hypothesis state that the same 'nuclear winter' effect would occur if 100 conventional firestorms were ignited. A much larger number of firestorms, in the thousands, was the initial assumption of the computer modelers who coined the term in the 1980s. These were speculated to be a possible result of any large scale employment of counter-value airbursting nuclear weapon use during an American-Soviet total war. This larger number of firestorms, which are not in themselves modeled, are presented as causing nuclear winter conditions as a result of the smoke inputted into various climate models, with the depths of severe cooling lasting for as long as a decade. During this period, summer drops in average temperature could be up to 20 °C (36 °F) in core agricultural regions of the US, Europe, and China, and as much as 35 °C (63 °F) in Russia. This cooling would be produced due to a 99% reduction in the natural solar radiation reaching the surface of the planet in the first few years, gradually clearing over the course of several decades. On the fundamental level, since the advent of photographic evidence of tall clouds were captured, it was known that firestorms could inject soot smoke/aerosols into the stratosphere but the longevity of this slew of aerosols was a major unknown. Independent of the team that continue to publish theoretical models on nuclear winter, in 2006, Mike Fromm of the Naval Research Laboratory, experimentally found that each natural occurrence of a massive wildfire firestorm, much larger than that observed at Hiroshima, can produce minor 'nuclear winter' effects, with short-lived, approximately one month of a nearly immeasurable drop in surface temperatures, confined to the hemisphere that they burned in. This is somewhat analogous to the frequent volcanic eruptions that inject sulfates into the stratosphere and thereby produce minor, even negligible, volcanic winter effects. A suite of satellite and aircraft-based firestorm-soot-monitoring instruments are at the forefront of attempts to accurately determine the lifespan, quantity, injection height, and optical properties of this smoke. Information regarding all of these properties is necessary to truly ascertain the length and severity of the cooling effect of firestorms, independent of the nuclear winter computer model projections. Presently, from satellite tracking data, stratospheric smoke aerosols dissipate in a time span under approximately two months. The existence of any hint of a tipping point into a new stratospheric condition where the aerosols would not be removed within this time frame remains to be determined. The nuclear winter scenario assumes that 100 or more city firestorms are ignited by nuclear explosions, and that the firestorms lifts large amounts of sooty smoke into the upper troposphere and lower stratosphere by the movement offered by the pyrocumulonimbus clouds that form during a firestorm. At 10–15 kilometres (6–9 miles) above the Earth's surface, the absorption of sunlight could further heat the soot in the smoke, lifting some or all of it into the stratosphere, where the smoke could persist for years if there is no rain to wash it out. This aerosol of particles could heat the stratosphere and prevent a portion of the sun's light from reaching the surface, causing surface temperatures to drop drastically. In this scenario it is predicted that surface air temperatures would be the same as, or colder than, a given region's winter for months to years on end.