http://www.jpost.com/HealthAndSci-Tech/ScienceAndEnvironment/Article.aspx?id=175648

By JUDY SIEGEL-ITZKOVICH
15/05/2010 23:49

Also, Weizmann Institute researcher reveals gene responsible for producing sweet, pink tomato loved by diners in the Far East.

Where there’s smoke, there’s fire, and where there’s air pollution, local weather patterns, rainfall and thunderstorm intensity can be affected. So say Tel Aviv University researchers and colleagues in other institutions who recently published their findings in Geophysical Research Letters.

In the new study, Prof. Colin Price, head of TAU’s department of geophysics and planetary science, researched data on lightning patterns in the Amazon to show how clouds are affected by particulate matter emitted by the fires used for slash-and-burn foresting practices. His findings could be used by climate change researchers trying to understand the impact of pollution.

Along with researchers at the Weizmann Institute and the Open University, Price demonstrated how pollution’s effects on cloud development could negatively affect our environment. While low levels of particulate matter actually help thunderstorms develop, the reverse is true once a certain concentration is reached; the particles then inhibit the formation of clouds. “The clouds just dry up,” he says.

Scientists have known for some time that man-made aerosols affect cloud formation, but scientific findings have been inconclusive. How clouds and storms change in response to air pollution is central to the debate about climate change and global warming.

But how man-made pollution affects clouds, rainfall and weather patterns remains poorly understood, and natural particulates such as those generated by Iceland’s recent volcano eruptions may add to this effect. The thick volcanic ash cloud absorbs solar radiation, heating the upper atmosphere, similar to forest fire smoke, and can hence also affect the development of clouds, Price said.

While studying the climate of the Amazon forest during its dry season, the researchers noticed how thousands of man-made forest fires injected smoke into the atmosphere. Since thunderstorms still occur during the dry season, it was the perfect opportunity for studying the effects of these particulates on cloud development.

Cloud droplets form on small particles called cloud condensation nuclei (CCN). As the number of CCN increase due to fire activity, lightning activity increased in the storms ingesting the smoke. More CCN implies more small droplets that can be carried aloft into the parts of the cloud where lightning is generated. Increased lightning activity generally also implies increasing rainfall over the Amazon. But when particulate matter became too dense, they observed, clouds didn’t form, and ightning activity diminished dramatically.

These results may have significant implications for polluted regions that rely on rainfall for agriculture. “One of the most debated topics related to future climate change is what will happen to clouds, and rainfall if the earth warms up,” says Price, “and how will clouds react to more air pollution?”