Understanding what will happen to the Earth’s atmosphere after a nuclear war sets a bunch of cities on fire has long been one of science’s most terrifying hypotheticals.There are models, guideposts, and more or less similar precedents, including the two American nuclear strikes against Japan in 1945. The 1991 eruption of Mount Pinatubo in the Philippines, or the 1883 eruption of Krakatoa in Indonesia, for example, sent up plumes of smoke whose global atmospheric effects were also well studied.But one of the most compelling and revealing comparisons for nuclear winter is wildfires, for which Canada is a global hotspot. A new report by American researchers in the journal Science shows how the devastating wildfires in British Columbia in the summer of 2017 offer new and frightening insights into the climatic effects of nuclear war.Basically, they discovered that when smoke and soot are forced up beyond the rainy troposphere into the dry atmosphere, they linger, then rise even higher as they absorb sunlight, and remain detectable even many months later.It was on Aug. 12, 2017, that the Pacific Northwest wildfires threw up a pyrocumulonimbus cloud, the billowing, cauliflower-shaped behemoth that blots out the sun and causes havoc with local weather. It was not only the biggest such cloud of the year, but the biggest ever observed.
An enormous cloud of smoke from intense wildfires drifted over northern Canada on August 15, 2017. The image is a mosaic composed from several satellite overpasses because the affected area was so large.
NASA Earth Observatory
Three days later, the province declared a state of emergency. At the peak of the crisis, thousands of people were evacuated, hundreds of fires were burning, and by far the largest area of land ever burned in a season — about 12,000 square kilometres — had been reduced to a blackened, wrecked landscape. (That record was surpassed the following year.)The smoke plume was so big, in fact, that the only applicable modelling of how it would behave had been done to forecast a nuclear winter after the Cold War went hot, with cities burning around the world, injecting soot into the atmosphere.This was a less extreme version of nuclear winter, observed in real time with ground based lidar (laser radar) and by satellites.“The observed rapid plume rise, latitudinal spread, and photochemical reactions provide new insights into potential global climate impacts from nuclear war,” the researchers from Rutgers University write in their report. What was curious was that it rose, from 12 kilometres in August to nearly double that height by mid-October. Only then did it start to slowly fall, at maybe half a kilometre per month. It spread all through the Northern Hemisphere stratosphere, and was still detectable by the following April.“This process of injecting soot into the stratosphere and seeing it extend its lifetime by self-lofting, was previously modelled as a consequence of nuclear winter in the case of an all-out war between the United States and Russia, in which smoke from burning cities would change the global climate,” said Alan Robock, distinguished professor of environmental sciences at Rutgers University-New Brunswick, in a statement. “Even a relatively small nuclear war between India and Pakistan could cause climate change unprecedented in recorded human history and global food crises.”One of the key predictions of nuclear winter models is that once smoke reaches the upper troposphere, the lowest atmospheric level that contains nearly all the water, it will then be heated by the sun and “self-loft” into the stratosphere, where there is no rain to wash it out.“The 2017 fires studied here represent the first observational evidence that such a rise actually occurs,” the authors report.They also studied the “photochemical loss of organic carbon,” in which sunlight breaks down molecules, and discovered that, although it happens, the smoke remained detectable in the stratosphere for an “unusually long” eight months.“Most nuclear winter studies have assumed that the organics in smoke can be ignored because of their rapid loss from photo-chemical reactions,” they wrote. “This study calls that assumption into question given the observed persistence of the smoke in the 2017 fire plume.”The study is part of a larger Rutgers research project to model the climatic effects of nuclear war on food production and the risk of famine.• Email: firstname.lastname@example.org | Twitter: josephbrean