Global Warming: Fiction: Scientists in the 1970s Were Predicting a Coming Ice Age
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 The solar brightening durting that time could not have superseded the greenhouse effect as main cause of global warming, since land temperatures increased by 0.8oC from 1960 to 2000, even though solar brightening did not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:
Human activities can cause global climate change on a relatively short time scale
Legislation can mitigate that climate change