During 1993 scientists from around the world gathered in North-Western Tasmania for the final phase of a two-year experiment to find the likely impact of air pollution on global temperatures.

They were to gather information on clouds from ground-based measurements, aircraft flights and satellite instruments.

"The number of particles in clouds determines how much sunlight is reflected back into space," said Dr Jorgen Jensen, a Senior Research Scientist at the CSIRO Division of Atmospheric Research.

"In the clean air of the southern hemisphere, most of the particles come from algae in the ocean. However, in the polluted northern hemisphere, industrialisation is steadily increasing the number of particles in the air," Dr Jensen said.

Dr Jensen and his team were to fly their Fokker research plane through and above clouds. At the same time, colleagues were to probe the clouds from below and monitor air composition at the Cape Grim Baseline Air Pollution Station.

The first stage of the experiment, dubbed SOCEX (Southern Ocean Cloud Experiment) took place in winter 1993, when natural emissions of sulfur gases from the ocean were low. These gases generate natural particles that act as cloud nuclei.

During warm conditions, ocean plankton flourish, generating more particles. Scientists were to compare summertime clouds, forming in air containing high particle levels, with those formed in winter air.

"The Southern Ocean is a natural laboratory. By comparing summer measurements with those we made in winter, we can discover how increased levels of cloud nuclei change cloud properties," Dr Jensen said.

Clouds have a major impact on global temperatures. Without them, the world’s average temperature would be much warmer than it is now.