More desert poses problems for people in Nigeria, Chad, and Cameroon who live near Lake Chad. The lake is an important source of water on the southern edge of the Sahara. Today, it’s drying up.
“Should the rains fail in a one or two-year period due to El Niño or something else, then there could be famine,” said Nigam, referring to the periodic climate pattern over the Pacific Ocean that leads to hotter and dryer conditions in Africa.
But a few factors were at play that suggest more work is necessary to understand exactly why the Sahara is growing, said Nigam.
Climate and rainfall records show that a phenomenon known as the Atlantic Multidecadal Oscillation, or AMO, alters the temperature of the surface of the Atlantic Ocean, which in turn alters rainfall patterns in the Sahel, the area of north-central Africa along the Sahara’s southern rim. From the 1950s to the 1980s, AMO led to colder temperatures that resulted in less rainfall in that period.
Nigam and his colleagues concluded that AMO was responsible for around two-thirds of the Sahara’s expansions. Climate change stemming from greenhouses gases, they said, was responsible for the other third.
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Today, AMO is heating up, suggesting the Sahel should receive more rainfall. But human-caused climate change could have the opposite influence, Nigam said. Since AMO takes place over decades, it’s hard to parse out which force is
exerting more influence over weather in the desert, the professor added.
Nigam and his colleagues intend to study the question further, including looking at other deserts around the world to see how they might be coping with new natural and manmade weather cycles.
“Are the two beginning to interact,” Nigam said, “or are the two operating fundamentally independently? We don’t know the answer to that.”