Global cooling is no longer expected. The original prediction was partly flawed. Decreases in air pollution in many countries means that now more sunlight reaches the Earth’s surface.

In the 1970s several scientific articles discussed the possibility of a new ice age at some point in the future. One of the sources of this idea may have been a 1971 paper by Stephen Schneider, a climate researcher in the USA. Schneider's article suggested that the cooling effect of dirty air, which scatters the Sun’s heat back into space, could outweigh the warming effect of the greenhouse gas carbon dioxide, potentially leading to an ice age if air pollution quadrupled.

This scenario was seen as plausible by many other scientists, as the Earth had been cooling since the 1940s. Furthermore, it had also become clear that the interglacial period in which we live had already lasted an unusually long time. However, Schneider soon realised he had overestimated the cooling effect of air pollution and underestimated the effect of carbon dioxide, meaning warming was more likely than cooling in the long run.

Since the 1980s however there have been quite successful attempts, at least in some countries, to clean up the air by reducing the emission of industrial pollutants. At the same time emissions of greenhouse gases have being increasing relentlessly. The net effect has been a strong increase in global warming. According to the latest Intergovernmental Panel on Climate Change report (2007), it is more than 90% certain that the world is already warming as a result of human activity.