In the South Pacific, the study shows, these two effects sometimes cancel each other out, resulting in highly uncertain rainfall projections. Results of the study are published in the 28 October online issue of Nature Climate Change.
Storms in the South Pacific on 8 Feb., 2012. Image courtesy Digital Typhoon, National Institute of Informatics.
Credit: Image courtesy Digital Typhoon, National Institute of Informatics.
The largest rainband in the Southern Hemisphere – the South Pacific Convergence Zone (SPCZ) – is the main source of rainfall for South Pacific island nations. Changes in this rainfall band would have severe consequences for the vulnerable island nations already having to adapt to accelerating sea level rise. Yet, very little is known about how this 8,000-km-long climate feature will respond to greenhouse warming.
"One reason why the SPCZ projections are so elusive is that many climate models are notoriously poor in simulating this important rainband, even under present-day climate conditions," says Postdoctoral Fellow Widlansky at the International Pacific Research Center. "We were able to overcome some model shortcomings in simulating South Pacific climate by removing model deviations from observed sea surface temperatures."
With the resulting improvements in climate model performance, Widlansky, Timmermann, and colleagues could identify two competing mechanisms affecting rainfall trends in the South Pacific.
"We have known for some time that rising tropical temperatures will lead to more water vapor in the atmosphere," explains Timmermann, professor of oceanography at the International Pacific Research Center and the University of Hawaii at Manoa. "Abundant moisture tends to bring about heavier rainfall in regions of converging winds such as the SPCZ." Scientists refer to this as the "wet gets wetter" climate change mechanism.
"Nearly all climate change model simulations, however, suggest the equatorial Pacific will warm faster than the SPCZ region. This uneven warming is likely to pull the rainband away from its normal position, causing drying in the Southwest Pacific and more equatorial rainfall," Timmerman goes on to say. The study refers to this as the "warmest gets wetter" mechanism.
Widlansky adds, "When we evaluated the latest climate change experiments being conducted by international climate modeling groups, we saw that these competing mechanisms are the cause for uncertainty in the SPCZ rainfall projections."
The scientists found that depending upon the degree of tropical warming expected this century, one or the other mechanism is more likely to win out. With moderate warming, weaker sea surface temperature gradients are likely to shift the rainband towards the equator, potentially causing drying during summer for most Southwest Pacific island nations. For much higher warming possible by the end of this century, the net effect of the opposing mechanisms is likely a shift towards more rainfall for the South Pacific islands.
"To be more definite in our projections, however, we need more extensive observations in the South Pacific of how clouds and rainfall form and how they respond to such climate phenomena as El Niño. Before we have more confidence in our calculations of the delicate balance between the two climate change mechanisms, we need to be able to simulate cloud formations more realistically," says Timmermann.
Citation: Widlansky, M. J., Timmermann A., Stein K., McGregor S., Schneider N., England M. H., Lengaigne M., & Cai W. (2012): Changes in South Pacific rainfall bands in a warming climate. Nature Climate Change. [DOI: 10.1038/NCLIMATE1726] (Advance Online Publication)
Weblink to summary at http://dx.doi.org/10.1038/NCLIMATE1726.
Funding came from the U.S. Department of Energy, Grant DEFG02-07ER64469; US National Science Foundation, Grant 1049219, and the institutional grants of the International Pacific Research Center (JAMSTEC, NASA, and NOAA).
Researcher contacts: Matthew J. Widlansky, firstname.lastname@example.org, 808-956-2822 Axel Timmermann, email@example.com, 808-956-2720
International Pacific Research Center Media Contact: Gisela E. Speidel (808)956‐9252; Email firstname.lastname@example.org
Gisela Speidel | EurekAlert!
UCI and NASA document accelerated glacier melting in West Antarctica
26.10.2016 | University of California - Irvine
Ice shelf vibrations cause unusual waves in Antarctic atmosphere
25.10.2016 | American Geophysical Union
Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.
So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
28.10.2016 | Power and Electrical Engineering
28.10.2016 | Life Sciences
28.10.2016 | Life Sciences