Lead in clouds could alter patterns of rain, snowfall

London, April 20 (IANS) Lead generated by human activities causes clouds to form at warmer temperatures and with less water, a new study has found.

This could alter the pattern of both rain and snow in a warmer world. The lead-laden clouds come with a silver lining, however.

Under some conditions, these clouds let more of the earth’s heat waft back into space, cooling the world slightly. Atmospheric lead primarily comes from human sources such as coal.

Researchers from the US, Switzerland and Germany collaborated in the study.

“We know that the vast majority of lead in the atmosphere comes from man-made sources,” said atmospheric chemist Dan Cziczo of the US Department of Energy’s (DoE) Pacific Northwest National Lab and study author.

“And now we show that the lead is changing the properties of clouds and therefore the balance of the sun’s energy that affects our atmosphere.”

Scientists first attempted to goad rain from the sky with silver and lead iodide in the 1940s. Since then, researchers have known that lead can pump up the ice crystals in clouds.

But daily human activities also add lead to the atmosphere.

The top sources include coal burning, small airplanes flying at the altitude where clouds form, and construction or wind freeing lead from the ground. Cziczo and colleagues wanted to know how lead from these sources affects clouds.

“This work highlights how complex these interactions between lead and water vapour and temperature are,” said Cziczo. “They’re not as simple as greenhouse gases.”

Future work will look at the type of lead and how much is needed to affect clouds and precipitation, as well as the atmospheric distribution of the metal dust, said a DoE release.

These findings are slated for publication in the May issue of Nature Geoscience.