Severe African Drought Caused by Air Pollution in the Northern Hemisphere: The Danger of Aerosols

First Posted: Jun 10, 2013 10:50 AM EDT

Drought has plagued Africa for years. Yet it reached its worst in the 1980s when Lake Chad, a shallow body of water used to cultivate crops in neighboring countries, almost dried out completely. Now, though, researchers have pinpointed what may have caused this drought in part. It turns out that air pollution from the Northern Hemisphere may have aided the excessively dry conditions.

In the 1960s, 70s and 80s, coal burning factories in the United States and Europe pumped aerosols into the atmosphere. This caused the entire Northern Hemisphere to cool, shifting tropical rain bands to the south. This, in turn, caused rains to no longer reach the Sahel region, a band that spans the African continent just below the Sahara desert.

Yet that changed when clean-air legislation was finally passed in the U.S. and Europe. The rain band shifted back and the drought lessened. Yet the fact remains that human impacts drastically changed the world's climate, showing that what happens in one area of the world can affect another area.

Actually seeing this shift in rainfall patterns and correlating it to air quality was no small task, though. The researchers had to look at precipitation from all rain gauges that had continuous readings between 1930 and 1990. In fact, while conducting this study they found that northern India and South America also experienced a drier climate. Yet countries that were on the southern edge of the rain band, such as northeast Brazil and the African Great Lakes, were actually wetter than normal.

In order to find out what might have caused these shifts, the researchers then looked at 26 climate models used by the Intergovernmental Panel on Climate Change. In the end, they found that cooling from aerosols in the Northern Hemisphere was the primary reason behind the shift of the rain band.

"We think people should know that the particles not only pollute air locally, but they also have these remote climate effects," said lead author Yen-Tin Hwang, a UW doctoral student in atmospheric sciences, in a press release.

Fortunately for Africa, though, legislation has helped clean up the air and has caused the rain band to shift back where it belongs. Yet it does show the global interconnectedness of the Earth's climate. Pollution in one country can also affect other regions, which means that it's more important than ever to have governments working together in order to curtail global problems such as temperature and sea level rise.

The findings are published the journal Geophysical Research Letters.

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