Greenhouse Gases May Cause Rainfall in Africa and Impact its Future Climate

It turns out that greenhouse gases may not just be causing temperatures to rise. They're also responsible for the rainfall in Africa. Scientists have found that a period known as the African Humid Period that began after a long dry spell could potentially be blamed on greenhouse gases.

The African Humid Period lasted nearly 10,000 years and occurred just after the end of the last ice age. During this time, cumulative rainfall was extremely high. Yet exactly what caused this rainfall has remained a mystery for years.

In order to find out what might have caused this increased rainfall, the researchers focused on the era following the last ice age. When ice sheets first began retreating about 21,000 years ago, there was a long dry spell in central Africa. Then, about 14,700 years ago, rainfall in Africa abruptly increased in two separate regions: one north of the equator, the other south.

As the Earth emerged from the ice age, greenhouse gases-such as carbon dioxide and methane-increased significantly. In fact, they rose to almost pre-industrial levels. As the planet continued warming, ice sheets melted and the influx of fresh water weakened the Atlantic Meridional Overturning Circulation, which brings warm water up from the tropics and keeps Europe temperate.

As the Atlantic ocean current weakened, precipitation moved southward toward the southernmost part of Africa. This suppressed rainfall during the dry period. But when the ice sheets stopped melting, the circulation strengthened and brought back the precipitation. This, coupled with the orbital shift and warming atmosphere caused by greenhouse gases, triggered the African Humid Period.

"This study is important not only because it explains a long-standing puzzle, but it helps to validate model predictions of how rising greenhouse gas concentrations might change rainfall patterns in a highly populated and vulnerable part of the world," said Peter Clark, co-author of the new study, in a news release.

The findings reveal that greenhouse gases did have a role in causing this rainfall. More specifically, it shows what conditions we may face in the future.

The findings are published in the journal Science.

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