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 NASA sees quick development of Hurricane Dora
27.06.2017 | NASA/Goddard Space Flight Center

nachricht Collapse of the European ice sheet caused chaos
27.06.2017 | CAGE - Center for Arctic Gas Hydrate, Climate and Environment

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>