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Pacific Ocean Temperature Changes Point to Natural Climate Variability
Analysis of long-term changes in Pacific Ocean temperatures may provide additional data with which to evaluate global warming hypotheses. "Abrupt changes in water temperatures occurring over intervals of up to 25 years suggest that global warming may result as much from natural cyclical climate variations as from human activity," said Benjamin Giese, oceanography professor in the College of Geosciences.
"Climate models constructed here at Texas A&M University were used to analyze ocean surface temperature records in the tropical Pacific since 1950. The results suggest that as much as one-half of all global surface warming since the 1970s may be part of natural variation as distinct from the result of greenhouse gases."
Giese and graduate student Amy J. Bratcher published the results of their analysis in the October 8, 2002, issue of Geophysical Research Letters.
Surface air temperature records maintained over the past 120 years serve as the main evidence for hypotheses linking global warming to increased greenhouse gases generated by humanmade (anthropogenic) causes. These records show the average global air temperature has risen by about one-half degree centigrade over the last 50 years. But while the general air temperature trend seems to be undisputedly upward, this upward trend varies considerably. "How much of this variability is attributable to natural variations and how much is due to anthropogenic contributions to atmospheric greenhouse gases has not yet been resolved," Giese said. "Recent studies indicate that it is difficult to separate intrinsic natural variance from anthropogenic forcing in the climate system."
Giese believes their analysis of tropical Pacific Ocean data indicates long-term upward changes in ocean temperatures that precede global surface air temperature changes by about four years. These ocean temperature fluctuations are in turn preceded by an increase in subsurface water temperatures by about seven years. "Thus, the results suggest that much of the decade to decade variations in global air temperature may be attributed to tropical Pacific decadal variability," Giese observed. "The results also suggest that subsurface temperature anomalies in the southern tropical Pacific can be used as a predictor of decadal variations of global surface air temperature." For example, in 1976 an abrupt change in the temperature of the tropical Pacific Ocean preceded a rise of two-tenths of a degree in global air temperatures.
"This phenomenon looks like El Nino, but with a much longer time scale -- El Nino occurs over a period of from nine to 12 months, but this fluctuation lasts for about 25 years," he continued. "In 1976, the ocean temperature change in question occurred very quickly, moving from cooler than normal to warmer than normal in about a year."
Bratcher and Giese report that now conditions in the tropical Pacific are similar to those prior to the 1976 climate shift, except with the opposite sign. If conditions develop in a similar way, then the tropical Pacific could cool back to pre-1976 conditions. "The subsurface tropical Pacific has shown a distinct cooling trend over the last eight years, so the possibility exists that the warming trend in global surface air temperature observed since the late 1970s may soon weaken," Giese observed. "This natural variation would help to counter the greenhouse gas warming effect. In fact, careful study reveals that global warming and cooling has occurred in the past in cyclical patterns."
Giese's work involves constructing computer models that incorporate years of weather data to reveal recurring patterns of oscillation and help identify mechanisms that may affect climate. He focuses on climate oscillations that are not directly forced by such things as changing amounts of sunlight, but instead are mechanisms of internal climatic variation for which scientists have as yet isolated no particular cause.
"Our model results terminated at the end of 2001," he said. "Now we're waiting to see what their long-term effects may be on global temperatures. Giese also notes, "Our results don't preclude the possibility that anthropogenic sources of greenhouse gases have contributed to global warming. We're just suggesting that the human forced portion of global warming may be less than previously described."
Researchers Use Bran to Filter Arsenic, HCHs Out of Wastewater
Researchers from Germany's Fraunhofer Institute for Interfacial Engineering and Biotechnology, in collaboration with GUTec mbH, have developed a mobile wastewater treatment system for a large chemical company that uses bran to remove arsenic and chlorinated hydrocarbons (hexachlorocyclohexane, or HCHs) from wastewater. The system combines an electrochemical process with bio-adsorbers made from chemically modified bran.
"You can get bran from grain mills for a few Euros per metric hundredweight. We modify it chemically and use its hydrophobic properties, so that it can bind the toxic substances," said Dr. Manfred Kuhn of Fraunhofer IGB.
With the aid of the newly developed system, arsenic can be bound almost completely, except for 0.004 milligrams per liter, and hexachlorocyclohexane can be bound, except for 0.13 micrograms per liter. The researchers say it's possible to desorb the arsenic and the hexachlorocyclohexane in order to use the bio-adsorber a number of times. However, it's more economical to dispose of the system via combustion or composting.
At 2.5 meters long, 1.3 meters wide and 2 meters high, the system is highly flexible and can be used at different locations. It can be operated continuously, fully automatically, as well as in batch mode.
Arctic Perennial Sea Ice Could be Gone by End of the Century
A National Aeronautics Space Administration (NASA) study finds that perennial sea ice in the Arctic is melting faster than previously thought -- at a rate of nine percent per decade. If these melting rates continue for a few more decades, the perennial sea ice will likely disappear entirely within this century, due to rising temperatures and interactions between ice, ocean and the atmosphere that accelerate the melting process. The study also finds that temperatures in the Arctic are increasing at the rate of 1.2 degrees Celsius (2.2 Fahrenheit) per decade.
Perennial sea ice floats in the polar oceans and remains at the end of the summer, when the ice cover is at its minimum and seasonal sea ice has melted. This year-round ice averages about three meters (9.8 feet) in depth, but can be as thick as seven meters (23 feet). Melting sea ice would not affect sea levels, but it could profoundly impact summer shipping lanes, plankton blooms, ocean circulation systems, and global climate.
"If the perennial ice cover, which consists mainly of thick multi-year ice floes, disappears, the entire Arctic Ocean climate and ecology would become very different," said Josefino Comiso, a researcher at NASA's Goddard Space Flight Center, Greenbelt, Md., who authored the study.
Comiso used satellite data to track trends in minimum Arctic sea ice cover and temperature over the Arctic from 1978 to 2000. Since sea ice does not change uniformly in terms of time or space, Comiso sectioned off portions of the Arctic data and carefully analyzed these sections to determine when ice had reached the minimum for that area each year. The results were compiled to obtain overall annual values of perennial sea ice. Prior to the complete data provided by satellites, most records came from sparsely located ocean buoys, weather stations and research vessels.
The rate of decline is expected to accelerate due to positive feedback systems between the ice, oceans and atmosphere. As temperatures in the Arctic rise, the summer ice cover retreats, more solar heat gets absorbed by the ocean and more ice gets melted by a warmer upper water layer. Warmer water may delay freezing in the fall, leading to a thinner ice cover in the winter and spring, which makes the sea ice more vulnerable to melting in the subsequent summer. Also, the rise in summer ice temperatures could lengthen the summers, allowing earlier spring thaws and later freeze dates in the fall, causing further thinning and retreat of perennial ice.
Comparing the differences between Arctic sea ice data from 1979 to 1989 and data from 1990 to 2000, Comiso found the biggest melting occurred in the western area (Beaufort and Chukchi Seas) while considerable losses were also apparent in the eastern region (Siberian, Laptev and Kara Seas). Also, perennial ice actually advanced in relatively small areas near Greenland.
In the short term, reduced ice cover would open shipping lanes through the Arctic. Also, massive melts could increase biological productivity, since melt water floats and provides a stable layer conducive to plankton blooms. Also, both regional and global climate would be impacted, since summer sea ice currently reflects sunlight out to space, cooling the planet's surface and warming the atmosphere.
While the latest data came too late to be included in the paper, Comiso recently analyzed the ice cover data up to the present and discovered that this year's perennial ice cover is the least extensive observed during the satellite era.
The study appears in the late October issue of Geophysical Research Letters, and was funded by NASA's Cryospheric Sciences Program and the NASA Earth Science Enterprise/Earth Observing System Project. The mission of NASA's Earth Science Enterprise is to develop a scientific understanding of the Earth System and its response to natural or human-induced changes to enable improved prediction capability for climate, weather and natural hazards.
For more information, please visit www.gsfc.nasa.gov/topstory/2002/1122seaice.html.
This article originally appeared in the 01/01/2003 issue of Environmental Protection.