NEWS OF THE WEEK CLIMATE
CHANGE
MODELS FORECAST QUICKER WARMING Average global temperatures may rise substantially faster than anticipated
T
W O N E W MODELS T H A T A O
count for uncertainties surrounding global climate change forecasts both conclude
Ice t h a t once covered much of Glacier National Park, Montana, is shrinking.
that global temperatures are likely to rise strongly by 2020-30 [Nature, 416,719 and 723 (2002)]. One study by Peter A. Stott MATERIALS
predicts average global temperatures will rise 0.3-1.3 °C (0.5-2.3 °F) and the other study by Thomas F. Stocker forecasts a rise of 0.5-1.1 °C above the average temperature for the 1 9 9 0 - 2 0 0 0 decade. In contrast, the average global temperature increased by only 0.6 ± 0.2 °C over the entire 20 th century The two studies take quite different approaches. Stott, of the Hadley Centre for Climate Prediction & Research, Bracknell, U.K., used a complex state-ofthe-art model that simulates in detail the circulation of the atmosphere and the oceans. It incorporates variations in solar output, volcanic activity greenhouse
SCIENCE
Flashy Fibers Reflect All Comers
T
he shimmering fibers shown below combine the strength of a polymer and the exquisite reflectivity of an omnidirectional mirror. They were made by MIT researchers led by Yoel Fink, an assistant professor of materials science and engineering [Science, 296, 510 (2002)]. The work opens avenues for tailoring the external optical properties of polymer fibers that could be used as telecommunications filters or to code fabrics or paper. Omnidirectional mirrors reflect light coming from all angles and polarizations. They can be constructed from multiple layers of transparent, nonconducting materials with very different indexes of refraction. Such mirrors are typically fragile, however, and restricted to planar geometries. Putting these mirrors onto fibers requires matching the optical and thermomechanical properties of the components, Fink says. The fibers shown are made from polylether sulfone) and arsenic triselenide, which have quite
different indexes of refraction but deform and start flowing at the same temperature. The fibers are drawn from a preform—a thick core of polylether sulfone) surrounded by 21 alternating layers of polylether sulfone) and arsenic triselenide. Because of the thermochemical matching, the preform retains its organization when heated. These particular fibers reflect in the infrared region and in parts of the visible region. The colors are due to optical interference, akin to the sheen of a thin oil layer on a puddle of water, Fink explains.—MAUREEN R0UHI
gas emissions, and aerosols. "It runs on a Cray supercomputer and is able to represent in some detail the atmospheric and oceanic processes," Stott says. In contrast, Stocker, professor of climate and environmental physics at the University of Bern, in Switzerland, and his coworkers employed a much simpler model that contains only a limited number of processes but "is capable of simulating the observed large-scale changes over the past 150 years," Stocker says. By running many simulations, his team was "able to consistently assess uncertainties." Stott's results show that changing emission scenarios makes a great deal of difference in the projected temperature rise. "For the fossil-fuel-intensive scenario, we estimate wanriing between 3 and 7 °C by 2100 compared with 1 to 3 °C for the scenario in which efforts are made to reduce fossilfuel use," he says. In his work, Stocker attempted to quantify uncertainties in the United Nations Intergovernmental Panel on Climate Change (IPCC) projection of a temperature rise of 1.4-5.8 °C by 2100. His results show there is a 40% probability that the global mean temperature will exceed the range projected by IPCC, but only a 5% chance it will fall under that range. Drew Shindell, research physicist at the National Aeronautics & Space Administration's Goddard Institute for Space Studies, says that Stott and Stocker made reasonable predictions with the information they had available. What could invalidate those predictions are the "things that most assuredly we don't understand," he says. One unknown is the sun's output, which has been measured by satellite for only 20 years. "We do not know for sure whether the sun will grow brighter or cooler over the next few decades," Shindell says. "However, the odds are high that we'll see a warming of 0.4-0.5 °C by 2020-30."-BETTE HILEMAN
8
C&EN / APRIL
22,
2002
HTTP://PUBS.ACS.ORG/CEN
