Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rising temperature difference between hemispheres could dramatically shift rainfall patterns in tropics

03.04.2013
One often ignored consequence of global climate change is that the Northern Hemisphere is becoming warmer than the Southern Hemisphere, which could significantly alter tropical precipitation patterns, according to a new study by climatologists from the University of California, Berkeley, and the University of Washington, Seattle.
The tropical rain band is clearly visible as an equatorial belt of clouds cutting just below the Sahara desert. Courtesy of GEOSPACE/SCIENCE photo library.

Such a shift could increase or decrease seasonal rainfall in areas such as the Amazon, sub-Saharan Africa or East Asia, leaving some areas wetter and some drier than today.

“A key finding is a tendency to shift tropical rainfall northward, which could mean increases in monsoon weather systems in Asia or shifts of the wet season from south to north in Africa and South America,” said UC Berkeley graduate student Andrew R. Friedman, who led the analysis.

“Tropical rainfall likes the warmer hemisphere,” summed up John Chiang, UC Berkeley associate professor of geography and a member of the Berkeley Atmospheric Sciences Center. “As a result, tropical rainfall cares a lot about the temperature difference between the two hemispheres.”

Chiang and Friedman, along with University of Washington colleagues Dargan M. W. Frierson and graduate student Yen-Ting Hwang, report their findings in a paper now accepted by the Journal of Climate, a publication of the American Meteorological Society. It will appear in an upcoming issue.

Generally, rainfall patterns fall into bands at specific latitudes, such as the Intertropical Convergence Zone. The researchers say that a warmer northern hemisphere causes atmospheric overturning to weaken in the north and strengthen in the south, shifting rain bands northward.

Impact of the Clean Air Act

Even though greenhouse gas warming of Earth has been going up since the 19th century, Chiang, Friedman and their team found no significant overall upward or downward trend in interhemispheric temperature differences last century until a steady increase beginning in the 1980s.

The researchers attribute this to human emissions of aerosols, in particular sulfates – from coal-burning power plants, for example – which cooled the Northern Hemisphere and apparently counteracted the warming effect of rising greenhouse gases until the 1970 U.S. Clean Air Act led to a downward trend in sulfur emissions. The act reduced pollution and saved more than 200,000 lives and prevented some 700,000 cases of chronic bronchitis, according to 2010 figures from the Environmental Protection Agency.

“Greenhouse gases and aerosols act in opposite directions, so for much of the 20th century they essentially canceled one another out in the Northern Hemisphere,” Chiang said. “When we started cleaning up aerosols we essentially leveled off the aerosol influence and allowed the greenhouse gases to express themselves.”

The regions most affected by this shift are likely to be on the bands’ north and south edges, Frierson said.

“It really is these borderline regions that will be most affected, which, not coincidentally, are some of the most vulnerable places: areas like the Sahel where rainfall is variable from year to year and the people tend to be dependent on subsistence agriculture,” said Frierson, associate professor of atmospheric sciences. “We are making major climate changes to the planet and to expect that rainfall patterns would stay the same is very naïve.”

20th century rainfall patterns

Many discussions of climate change focus on long-term trends in the average global temperature. The UC Berkeley and University of Washington researchers went a step further to determine how the temperature difference between the two hemispheres changed over the last century and how that may have affected tropical rainfall patterns.

Using more than 100 years of data and model simulations, they compared the yearly average temperature difference between the Northern and Southern hemispheres with rainfall throughout the 20th century and noticed that abrupt changes coincided with rainfall disruptions in the equatorial tropics.

The largest was a drop of about one-quarter degree Celsius (about one-half degree Fahrenheit) in the temperature difference in the late 1960s, which coincided with a 30-year drought in the African Sahel that caused famines and increased desertification across North Africa, as well as decreases in the monsoons in East Asia and India.

“If what we see in the last century is true, even small changes in the temperature difference between the Northern and Southern hemispheres could cause measureable changes in tropical rainfall,” Chiang said.

This bodes ill for the future, he said. The team found that most computer models simulating past and future climate predict a steadily rising interhemispheric temperature difference through the end of the century. Even if humans begin to lower their greenhouse gas emissions, the models predict about a 1 degree Celsius (2° F) increase in this difference by 2099.

As global temperatures rose over the course of the 20th century (top), the temperature between the two hemispheres changed little until the 1980s, though it has been rising since. Courtesy of Andrew Friedman.

While the average temperature of the Earth is increasing as a result of dramatic increases in atmospheric greenhouse gases, primarily carbon dioxide, the Earth is not warming uniformly. In particular, the greater amount of land mass in the north warms up faster than the ocean-dominated south, Chiang said. He and his colleagues argue that climate scientists should not only focus on the rising global mean temperature, but also the regional patterns of global warming. As their study shows, the interhemispheric temperature difference has an apparent impact on atmospheric circulation and rainfall in the tropics.

“Global mean temperature is great for detecting climate change, but it is not terribly useful if you want to know what is happening to rainfall over California, for example,” Chiang said. “We think this simple index, interhemispheric temperature, is very relevant on a hemispheric and perhaps regional level. It provides a different perspective on climate change and also highlights the effect of aerosols on weather patterns.”

The research was supported by the U.S. Department of Energy and the National Science Foundation.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Earth Sciences:

nachricht GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center

nachricht Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>