Climate Change Caused by Humans
Fiction: Scientists in the 1970s Were
Predicting a Coming Ice Age

Fiction: Scientists in the 1970s Were Predicting a Coming Ice Age:

A very common misconception is that scientists in the 1970s were predicting a coming ice age. Skeptics take this one step further and claim: How can we trust the predictions of scientists if they were predicting a coming ice age in the 1970s and now they are prediciting global warming! This may sound reasonable until one examines the literature in the 1970s. Peterson, Connolley, and Fleck (2008) did just that. Figure 1 below summarizes their findings:

Articles from the 1970s
Figure 1: Number of articles in the 60s and 70s related to climate change

During the period 1965 through 1979, their survey found 7 cooling papers, 19 neutral and 42 warming. In no year were there more global cooling papers than global warming. The most often cited news story related to global cooling is the Newsweek story shown below in Figure 2. (Mann, 2007)

1970s Climate CrockPeter Sinclair's Climate Crock of the Week: I Love the 70s!
Watch this video to learn more.

Global Dimming:

Global Dimming
Figure 2: Global dimming during 1940 and 1970 and Newsweek story

The cooling between 1940 and 1970 was likely a result of industrial pollution that produced sunlight-blocking aerosols, a phenomenon known as global dimming. As industry ramped up across the globe, much air pollution was being spewed out of smoke stacks along with carbon dioxide. This air pollution was blocking incoming sunlight much like that of a volcanic eruption and had the effect of masking the global warming that was well underway. Once clean air legislation began to pass across the globe, air pollution decreased considerably. Sulfate aerosols have declined significantly since 1970 with the Clean Air Act in the United States and similar policies in Europe. The Clean Air Act was strengthened in 1977 and 1990. According to the EPA (2008), from 1970 to 2005, total emissions of the six principal air pollutants, including particulate matter, dropped by 53% in the US. In 1975, the masked effects of trapped greenhouse gases finally started to emerge and have dominated ever since.

According to Wild, M., Ohmura, A. and Makowski, K. (2007) solar dimming was effective in masking greenhouse warming, but only up to the 1980s, when dimming gradually transformed into brightening. Since then, the uncovered greenhouse effect has revealed its full dimension, as manifested in a rapid temperature rise (+0.38.C/decade over land since mid-1980s). The solar brightening durting that time could not have superseded the greenhouse effect as main cause of global warming, since land temperatures increased by 0.8oC from 1960 to 2000, even though solar brightening did not fully outweigh solar dimming within that period.

Because of the rapid rate of industrialization of China, India, and other Asian countries in the last few decades, there is still considerable global dimming today. (Recall figure 2.9 that shows aerosols have a direct cooling effect of 0.5 ±0.4 W/m2 and an indirect cooling effect caused by clouds of 0.7 W/m2 with a range between 0.3 and 1.8 W/m2.) If these developing countries pass similar legislation, the rate of global warming will accelerate even faster.

Two important conclusions can be drawn from this data:

  1. Human activities can cause global climate change on a relatively short time scale
  2. Legislation can mitigate that climate change

Next: Climate Models & Accuracy

Scott A. Mandia
Professor - Physical Sciences
T-202 Smithtown Sciences Bldg.
533 College Rd.
Selden, NY 11784
(631) 451-4104

Last updated: 10/26/09