Tropical Atlantic Cooling and African Deforestation Correlate to Drought, Report Scientists

Dec 02, 2005

Against the backdrop of the Montreal Summit on global climate being held this week, an article on African droughts and monsoons, by a University of California, Santa Barbara scientist and others, which appears in the December issue of the journal Geology, underlines concern about the effects of global climate change.

Tropical ocean temperatures and land vegetation have an important effect on African monsoon systems, explains first author Syee Weldeab, a post-doctoral fellow in the Department of Earth Science at the University of California, Santa Barbara. The monsoons are critical to sustaining agriculture in equatorial Africa.

Weldeab says that man's reduction of inland vegetation cover through deforestation and overgrazing in equatorial Africa and increases in global temperatures through the emission of greenhouse gases will likely strongly affect the African monsoon system in the future.

"The weakening of the monsoon has a huge effect," says Weldeab, "resulting in shortages of harvests and hunger."

As vegetation is cleared, the land loses its capacity to retain heat and becomes cooler. As the land cools relative to the ocean, there is a larger gradient between the ocean temperature and the land causing less moisture to be pulled from the ocean air toward the land.

Weldeab and his colleagues studied cores from beneath the ocean floor of the Gulf of Guinea, in the tropical Atlantic just off the coast of Cameroon, to understand the history of climate in the area for the past 10,000 years. The cores contain foraminifera, tiny plankton shells that are composed of calcium and trace elements. By studying the ratios of magnesium and calcium in the shells, the scientists are able to correlate that information to past temperature changes in the ocean. In analyzing these records for the past 10,000 years, the scientists found three pronounced cooling periods which indicate drought.

Besides the ocean records, the scientists analyzed data from four lakes that are distributed across central Africa on the monsoon belt. The three sea surface cooling periods found by the scientists correlate to records of low lake levels. These clearly were times of drought; the land became more arid.

The authors state, "periods of drought likely brought about environmental hardship, triggering population migration, giving rise to changes in the modes of agricultural production, and influencing the fall or rise of civilizations."

Weldeab points out that the past 50 years are marked by deforestation and overgrazing much greater than that of the past, thus disturbing the climate system that results from the coupling of sea surface temperature and vegetation cover on land. "We can't predict how, but it is clear that this human-induced change will change the terrestrial and ocean system," he says. He notes that droughts in this region are currently occurring more frequently than in the past few thousand years, although the frequency of the droughts is unpredictable.

"People in less developed countries live from rain, harvests and animal husbandry," says Weldeab. "Drought directly affects them; they run out of food for people and animals."

Source: University of California, Santa Barbara

Explore further: Researchers highlight acousto-optic tunable filter technology for balloon-borne platforms

add to favorites email to friend print save as pdf

Related Stories

Weather history time machine

Oct 15, 2014

During the 1930s, North America endured the Dust Bowl, a prolonged era of dryness that withered crops and dramatically altered where the population settled. Land-based precipitation records from the years ...

What do wildfires have to do with climate change?

Oct 14, 2014

As the western U.S. faces its third year of severe drought, firefighters are still battling two large fires in California. The state, which is experiencing its worst drought since record keeping began in ...

How myths and tabloids feed on anomalies in science

Oct 02, 2014

There are many misconceptions about science, including how science advances. One half-truth is that unexpected research findings produce crises, leading to new theories that overturn previous scientific knowledge.

The case for a mission to Mars' moon Phobos

Oct 02, 2014

Ask any space enthusiast, and almost anyone will say humankind's ultimate destination is Mars. But NASA is currently gearing up to go to an asteroid. While the space agency says its Asteroid Initiative will ...

Recommended for you

The formation and development of desert dunes on Titan

47 minutes ago

Combining climate models and observations of the surface of Titan from the Cassini probe, a team from the AIM Astrophysics Laboratory (CNRS / CEA / Paris Diderot University) , in collaboration with researchers ...

'Eau de comet' is a bit of a stinker

1 hour ago

Rotten eggs, horse pee, alcohol and bitter almonds: this is the bouquet of odours you would smell if a comet in deep space could be brought back to Earth, European scientists said on Thursday.

The great world wide star count

2 hours ago

How many stars can you see at night? Right now people all over the world are being asked to go out and count them!

User comments : 0