What does global cooling look like?
In popular culture, the ice age is often depicted as the kingdom of eternal winter – endless snowy plains from the poles to the equator, and Siberian frosts at any time of the year. This vivid image is well suited to science fiction, but climate scientists mean much more modest changes by global cooling. Thus, at the maximum point of the last glaciation 18,000 years ago, when the climate was 6.5 degrees colder, the eternal glaciers reached only the modern northern borders of the United States, covering Scandinavia, the Baltic Sea region and the northern part of modern Russia. . The current middle lane was covered with steppe and tundra of Central Europe, France and Ukraine, and forest-steppes began in the south.
During the Little Ice Age of the 14th and 19th centuries, snowy winters became commonplace in Western Europe, and summers were often rainy and cloudy. This periodically led to crop shortages and mass starvation, and at the height of the cold weather, the temperature in Europe dropped by 1-2 degrees, so that even a winter ice sheet appeared in the Adriatic Sea. If global warming were suddenly replaced by a new Little Ice Age today, it would do great damage to the economy, but it would not become an existential challenge to civilization.
Finally, in the era of scientific observations of climate, “exercises” were made with a small imitation of nuclear winter. In 1815, the Indonesian volcano Tambora erupted, which in power (but not in consequences) was equivalent to the explosion of an 800-megaton atomic bomb. Launched more than 150 km from the ground3 The rocks and ash completely covered the sky for several days within a radius of hundreds of kilometers from the volcano. A large number of sulfur oxides entered the atmosphere, from which sulfate aerosols were formed, reflecting sunlight.
As a result, global temperatures dropped by 0.4-0.7 degrees, farmers faced crop shortages from frost and snowfall, and 1816 was the “year without summer.”
Only once in Earth’s history, it almost turned into a snowball – 700-600 million years ago, when glaciers reached tropical latitudes. However, according modern Either there were large polynyas in the spherical ice sheet, or the ice sheet was much smaller and ended well above the equator.
Who came up with the concept of nuclear winter?
The impact of nuclear explosions on the climate was first considered at the beginning of the Cold War. In 1952, the Americans intended to produce the world’s first hydrogen bomb test explosion with a yield of about 10 megatons during the Ivy Mike test, and some scientists have expressed concern about possible global cooling. According to this report In the same year, Major Lulejian of the U.S. Air Force, explosions with a capacity of 10-100 megatons lift a lot of dust into the stratosphere, and indeed, even if tests are carried out every few years, it can significantly affect the insolation of the earth’s surface. .
Since then, there has been regular debate among scientists about whether nuclear explosions could lead to an ice age, but these were brought to a new level by the American astronomer Carl Sagan in the early 1980s. He initially gained fame thanks to space exploration: Sagan in particular calculated that the surface of Venus was very dry and hot long before the Soviet missions, and he also suggested (and it turns out) that Jupiter’s moon Europa had an inland ocean (to be right). Sagan had a hand in nearly all American space exploration, from the world’s first interplanetary Venus Marine 2 and Martian Vikings to the Voyagers that discovered giant planets.
Sagan III. His first known work on the possible consequences of World War II was Nuclear Winter: The Global Consequences of Multiple Nuclear Explosions (originally by Richard Turco, but Sagan was the main public face of the concept), published in Science in 1983. In it, he and his colleagues used three models: a model of the behavior of microparticles thrown into the atmosphere, to estimate the amount of dust and smoke from nuclear explosions, and a radiative-convective model that allows you to correlate atmospheric particulate matter. the amount of heat reaching the earth’s surface.
According to simulations, in a nuclear power plant with a total efficiency of 5,000 megatons or more, dust and smoke will outshine the sun and cool down very quickly. Based on the average hemisphere temperature of 13 degrees Celsius, it could drop to -23 degrees Celsius three weeks after the eruptions.
The Stone Age is much colder than the Ice Age, and it really looks like an apocalyptic scenario. Sub-zero temperatures should last about two to three months, and a full return to original values is not expected even on the 300th day.
At the same time, the authors immediately make a reservation: these values u200bu200bare valid for an abstract ultra-continental climate. The ocean works like a giant heat collector, so temperature drops should be 70% less in coastal areas and 30% less in the open seas. However, the ocean does not store sunlight and so months of shading will kill many plants or seriously impair their growth in any case.
Around the same time, in the first half of the 1980s, similar calculations afflicted Soviet scientists Georgy Golitsyn and Alexander Gintsburg. Their paper contains almost no conclusive statements, but generally confirms the conclusions of Sagan and colleagues.
Oil Winter and Desert Storm
Humanity soon had a chance to test the methodology of such calculations. In 1990, Iraqi dictator Saddam Hussein captured Kuwait and threatened to set about 800 oil wells on fire if the Western coalition declared war on him.
Hearing this, Sagan and Richard Turco declarationIf the Iraqis fulfill the threat, it threatens the world with a “summerless year”-like global catastrophe.
The key moment for global cooling is the rise of soot particles into the stratosphere. Soot from burning oil is black, easily heated by the sun and rises. Scientists thought the effect of oil well fires might be like a nuclear winter.
The Western coalition launched the Desert Storm offensive, Saddam carried out the threat, and the fires could not be put out for months. As a result, no global climate catastrophes occurred in either 1991 or 1992, and this can easily be verified by the older generation.
How to solve According to physicist Peter Hobbs, the global impact of the smoke from the fires was minimal because 1) fewer particles were emitted than expected 2) the smoke was not as black as expected 3) the smoke did not rise into the atmosphere but remained high less than 6 kilometers 4) soot particles suspended in the atmosphere for a short time stays on and settles in a few days. Cooling was only local and limited to a few degrees drop in midday temperature. As a result, some of the numbers used to support the nuclear winter hypothesis, according to Hobbs, turned out to be inflated. As scientists later realized, a stream of smoke must rise from a large area to reach the stratosphere, and oil wells are still a point object.
Is it possible to predict the effect of an atomic explosion?
When modeling the effects of a nuclear conflict, scientists have no choice but to rely on assumptions. Modern climate models describing the effects of aerosols and soot on climate are considered reliable and accurate. However, for the results to be accurate, it is necessary to put the right amount of soot in them at different heights. For this, it is necessary to understand how much particulate matter will rise into the stratosphere due to fires in cities. In turn, before that you need to find out how many cities will be bombed and how well they burn.
And will cities be bombed? On the contrary, it makes sense that the primary target in any nuclear war should be the enemy’s arsenal of atomic bombs. The burning of missile silos, airfields, military bases, and troop positions is clearly incapable of producing the amount of smoke necessary for a nuclear winter.
If the cities are still burning, it is not clear how they will do it. For example, by versions A nuclear explosion buries combustible materials under building ruins, Russian fire researcher Iosif Abduragimov. The scientist also doubts that the atomic bomb would cause a firestorm in a modern metropolis modeled on Hiroshima.
“The combustible mass is distributed in “cells” – rooms, then apartments, then houses, etc. Cells isolated from each other by fireproof stone, concrete and reinforced concrete partitions. Therefore, in undestroyed houses (and even more so in demolished houses), these combustion centers of combustible materials and materials separated by non-combustible barriers will not necessarily coalesce into a single sustained fire that leads to a firestorm. ”
– writes Abduragimov. There’s another view in the scientific community, but either a full-scale experiment or a full-fledged multifactorial urban fire model could make the cut.
What do modern scientists think?
Overall, researchers have long abandoned the Sagan and Turco model, which predicts an apocalyptic cooling of 20-30 degrees. recently in one article Owen Tun and his colleagues calculated the consequences of hundreds of nuclear attacks on cities between India and Pakistan. The authors start from the complete combustion of combustible material in the entire fire area and do not model exactly how the soot enters the stratosphere, but speculate based on the results of previous studies. Calculations based on these assumptions showed that after such a war, the average global land temperature should have dropped by 4-8 degrees and the entire Earth by 2-5 degrees. This is comparable to the Ice Age of the Stone Age, but such a nuclear winter will last for about a dozen years.
The perspective described above dominates modern writing, but there is strong and legitimate opposition to it by prominent scholars. For example, experts from the Los Alamos Laboratory, where nuclear weapons were created, disagree with the concept of nuclear winter. They article It is based on a pyramid of proven physics models from 2018: the xRage environmental fireball model, the HIGRAD-FIRETEC fire development model and the CESM climate model. The target of a virtual bombardment was one of the suburbs of America’s metropolis of Atlanta, and to assess the impact on climate, the authors assumed 100 such strikes had occurred.
As scientists have found, only a small part of the work ends up in the stratosphere.
“70% of the initial mass of carbon particles, most of which are emitted to altitudes below 9 kilometers, falls as rain in the first month and 78% disappears in the first 2 months. The rest are moved to an altitude of more than 12 kilometers during the first week, ”the authors write.
As a result, nuclear winter does not occur in the model. Global cooling is limited to half a degree on average and will mainly affect the sub-polar regions, but this effect will disappear in five years.