Aerosol particle increase linked to more rainfall: study

By Nina Chestney, editing by Rosalind Russell
15 January 2012 LONDON (Reuters) – A rise in the atmosphere of aerosols – miniscule particles which include soot, dust and sulphates – has led to more rainfall in certain parts of the world and could provide vital clues for future climate predictions, a scientific study shows. A deeper understanding of rainfall patterns would aid scientists’ ability to predict changing trends in the climate. Aerosols can be produced from burning coal or gas, industrial and agricultural processes, or by the burning of forests. As well as being harmful for human health, they are blamed for causing air pollution such as smog and smoke. “For a range of conditions, increases in aerosol abundance are associated with the local intensification of rain rates,” said the study published in Nature Geoscience by scientists from Israel’s Weizmann Institute, NASA, and other institutions. “The relationship is apparent over both the ocean and land, and in the tropics, sub-tropics and mid-latitudes,” it added, which would include large parts of continents such as Africa, South America and Asia. The scientists said further work was needed on how aerosols influence regions with lower rainfall rates. A separate study last November also found that aerosols increase the frequency of rainfall. It is thought that large volcanic eruptions, which release sulphur dioxide into the atmosphere, have led to increased rainfall. Another uncertainty in future climate prediction is over the role of aerosols in cloud formation. It is thought clouds can be changed by aerosol particles which act as seeds in cloud droplet and ice formation, influencing the way clouds are formed. Heavier cloud formation could cool the earth’s surface temperature by reflecting light back into space. “A prerequisite to predicting rainfall variability is an understanding of how rain-producing clouds will respond to a changing environment,” the study said. Using satellite data, the scientists found evidence that aerosols do intensify clouds. “We also find that increases in aerosol levels are associated with a rise in cloud-top height,” they said.