The global cooling scare that never was

Ed Brayton’s blog, Dispatches from the Culture Wars, today highlights an article just released in the Bulletin of the American Meteorological Society that does a wonderful job of permanently dismantling one of the favorite tropes of the climate-change deniers… that most climate scientists in the 1970s were predicting an ice age, before they decided later to predict global warming.

The 1970s ice-age myth is one of those perennial favorites of conspiracy-mongering right wing morons. As the story goes, scientists in the 1970s proclaimed in breathless panic that coal-burning power plants would bring about an icy apocalypse by spewing enough sulfate aerosol filth into the upper atmosphere to darken the skies, blot out the Sun, and scatter enough sunlight back to space that the Earth would cool into a new ice age. According to the genetically-damaged conservatives who promote this myth, the imaginary World Cabal of Evil Hippie Scientists used the scare of global cooling to try and enact their vision of a Utopian coal-free world, but soon gave that up for an even better master plan… global warming. Even as recently as 2004, this paranoid fantasy got some traction, in Michael Crichton’s conspiracy fever dream State of Fear

“Just think how far we have come!” Henley said. “Back in the 1970s, all the climate scientists believed an ice age was coming. They thought the world was getting colder. But once the notion of global warming was raised, they immediately recognized the advantages. Global warming creates a crisis, a call to action. A crisis needs to be studied, it needs to be funded . . .”

(State of Fear, 2004)

Which shows just how low the formerly interesting author had sunk at that point. Not that insane fantasy should be surprising, coming from the same person who wrote Travels… wherein Crichton appears to sincerely describe his personal experiences seeing people’s auras. Look it up.

Anyway. The new AMS Bulletin article deconstructs the myth. Some researchers in the late 1960s and early 1970s began to examine data from Russian air pollution measurements and recent volcanic eruptions showing localized cooling effects resulting from aerosols, and rightly concluded that highly reflective dust particles in the upper atmosphere scatter sunlight, resulting in a net negative influence on retention of thermal energy in the troposphere. Yet even at that time, the influence of greenhouse gases on atmospheric thermal retention was recognized as more important on a global basis. As the AMS Bulletin article reports, between 1965 and 1979 only seven papers supporting a model of aerosol-induced global cooling were published in the peer-reviewed climatological literature, while 44 papers supporting a model of potential CO2-induced global warming were published in the same period.

Dust and sulfate aerosols can and do block sunlight from reaching the Earth’s surface, but such particles are generally heavier than air, and generally do not reach to stratospheric altitudes where they can be kept aloft for months and spread across a global range. Volcanic eruptions can accomplish that, as was observed following the eruption of Mt. Tambora (Indonesia) in 1815, which resulted in the Year Without a Summer in 1816. Similar but much milder effects were witnessed following the eruptions of Mt. St. Helens and Mt. Pinatubo. Global thermonuclear war could accomplish the same thing… which led Carl Sagan to warn about a potential “nuclear winter” effect following an atomic war on Earth. But aerosols from coal-burning plants cannot easily do that, and their effects on sunlight reaching the Earth’s surface are normally regional at worst.

The great irony is that sulfate aerosol effects really are real, and modern climate modeling must take regional cooling effects into account to accurately approximate observed temperature trends in North America, Europe and China. According to the results of climate model calculations presented by the Intergovernmental Panel on Climate Change (IPCC), failure to include regional cooling effects caused by aerosol shrouds over the industrialized (coal-burning) world causes models to overpredict temperatures. Basically, if the cooling influence of sulfate aerosols is excluded, the models results don’t fit reality. Only by including a modest amount of regional cooling caused by coal-derived aerosols produced by the world’s biggest coal-burning nations can climate be accurately understood.

Not only was there never a scientific consensus that the world is cooling due to burning coal, there was a widespread early consensus that CO2-induced warming was and is far more important. Not only that, taking account of regional aerosol cooling is required to figure out what is really happening with the weather.


~ by Planetologist on November 21, 2008.

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