Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pollution in Northern Hemisphere helped cause 1980s African drought

07.06.2013
Decades of drought in central Africa reached their worst point in the 1980s, causing Lake Chad, a shallow lake used to water crops in neighboring countries, to almost dry out completely.
The shrinking lake and prolonged drought were initially blamed on overgrazing and bad agricultural practices. More recently, Lake Chad became an example of global warming.

New University of Washington research, to be published in Geophysical Research Letters, shows that the drought was caused at least in part by Northern Hemisphere air pollution.

Aerosols emanating from coal-burning factories in the United States and Europe during the 1960s, ’70s and ’80s cooled the entire Northern Hemisphere, shifting tropical rain bands south. Rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert.

When clean-air legislation passed in the U.S. and Europe, the rain band shifted back, and the drought lessened.

Related research by the UW researchers and their collaborators shows that global warming is now causing the land-covered Northern Hemisphere to warm faster than the Southern Hemisphere, further reversing the pre-1980s trend.

Previous research has suggested a connection between coal-burning and the Sahel drought, but this was the first study that used decades of historical observations to find that this drought was part of a global shift in tropical rainfall, and then used multiple climate models to determine why.

“One of our research strategies is to zoom out,” said lead author Yen-Ting Hwang, a UW doctoral student in atmospheric sciences. “Instead of studying rainfall at a particular place, we try to look for the larger-scale patterns.”

To determine that the Sahel drought was part of a broader shift, the authors looked at precipitation from all rain gauges that had continuous readings between 1930 and 1990. Other places on the northern edge of the tropical rain band, including northern India and South America, also experienced dryer climates in the 1970s and ’80s. Meanwhile, places on the southern edge of the rain band, such as northeast Brazil and the African Great Lakes, were wetter than normal.

To understand the reason, authors looked at all 26 climate models used by the Intergovernmental Panel on Climate Change. Researchers discovered that almost all the models also showed some southward shift, and that cooling from sulfate aerosols in the Northern Hemisphere was the primary cause.

“We think people should know that these particles not only pollute air locally, but they also have these remote climate effects,” Hwang said.

Light-colored sulfate aerosols are emitted mainly by dirty burning of coal. They create hazy air that reflects sunlight, and also lead to more reflective, longer-lasting clouds.

People living in the Northern Hemisphere did not notice the cooling, the authors said, because it balanced the heating associated with the greenhouse effect from increased carbon dioxide, so temperatures were steady.

“To some extent, science messed this one up the first time around,” said co-author Dargan Frierson, a UW associate professor of atmospheric sciences. “People thought that a large part of that drought was due to bad farming practices and desertification. But over the last 20 years or so we’ve realized that that was quite wrong, and that large-scale ocean and atmosphere patterns are significantly more powerful in terms of shaping where the rains fall.”

The models did not show as strong a shift as the observations, Frierson said, suggesting that ocean circulation also played a role in the drought.

The good news is that the U.S. Clean Air Act and its European counterpart had an unintended positive effect beyond improved air quality and related health benefits. Although shorter-term droughts continue to affect the Sahel, the long-term drought began to recover in the 1980s.

“We were able to do something that was good for us, and it also benefited people elsewhere,” Frierson said.

The work was funded by the National Science Foundation. Sarah Kang at the Ulsan National Institute of Science and Technology in South Korea was a co-author.

For more information, contact Hwang at 206-543-0333 or yting@atmos.washington.edu and Frierson at 206-685-7364 or dargan@atmos.washington.edu

Hannah Hickey | EurekAlert!
Further information:
http://www.uw.edu
http://www.washington.edu/news/2013/06/06/pollution-in-northern-hemisphere-helped-cause-1980s-african-drought/

More articles from Earth Sciences:

nachricht New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg

nachricht Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>