Geotimes - December 2004

Geotimes

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Geophenomena

Corroding pipe organs
Extreme storms as climate warms

Corroding pipe organs

In August 1999, Armin Schoof, a professor of music and the organist at St. Jakobi Church in Lübeck, Germany, discovered severe cracks and holes in the lead pipes of the church’s famous Stellwagen organ. Fearing the loss of the 15th-century instrument, Schoof contacted researchers at the Göteborg Organ Art Center at Göteborg University, Sweden.

Lead and lead-alloy pipes in the Stellwagen organ at St. Jakobi Church in Lübeck, Germany, are corroding away. The organ was built in 1467, and still contains original pipes. Researchers are working to determine the cause of the decay. Courtesy of Carl Johan Bergsten.

Carl Johan Bergsten, a research engineer at the Göteborg Organ Art Center, gathered together a team of metallurgists, environmental chemists and organ restorers, and they soon found that the problem was more widespread: Of the 10,000 historic instruments remaining in Europe dating from the 15th to 17th centuries, the mysterious deterioration has already affected more than 1,000 — and possibly more. During the last few decades, this deterioration has accelerated. Unchecked, the corrosion of the metal pipes will change the sounds of these historic artifacts, perhaps even silencing them.

Most organ-builders restoring or repairing historical organs find pipe corrosion. Corrosion usually begins with cracks and holes in the foot of a metal pipe and continues to move upward toward its mouth, eventually causing a complete collapse. “If the corrosion reaches the mouth, the sound properties will gradually change and finally the pipe will be silent,” Bergsten says. “This is serious because the historical sound quality will be lost and the sounding cultural heritage is forever gone.”

Bergsten says that it is too early to draw any final conclusions about the cause of the corrosion. The project that he leads, called the Corrosion of Lead and Lead-Tin Alloys of Organ Pipes in Europe project (known as COLLAPSE), is addressing many factors inside churches, including changing temperature, humidity and condensation and indoor pollutants, such as acidic vapors released by wood in the organ. The researchers are also considering outdoor pollutants emitted from traffic, agriculture and industry.

Team members are now analyzing samples from affected pipe organs in Italy, Belgium, the Netherlands and Germany, and comparing them to samples from unaffected organs in similar climatic regions. Preliminary findings show that alone, inorganic pollutants, such as sulfur dioxide and nitrogen oxides, do not seem to be the culprit. However, Bergsten says, a combination of the factors could be causing the corrosion, something the team will test in field and laboratory analyses of different pollutants interacting in varying environmental conditions.

Researchers do know that not all types of pipes are equally prone to corrosion. Carla Martini, a metallurgist at the University of Bologna in Italy, says that so far, most analyses have been of lead-rich pipes containing less than 4 percent tin by weight. “The extent to which [the pipes] are affected by corrosion in a given environment changes with the composition of the alloy, namely with the tin content,” Martini says, with the most corrosion found in pipes containing 1.5 to 2 percent tin.

In some cases, earlier attempts at conservation might now be causing corrosion. While investigating the Stellwagen organ, researchers discovered the powdery residues of lead compounds that are usually produced by interactions with organic acids. Analysis of the air inside the organ found high concentrations of acetic acid, which corrodes lead even in very low concentrations. “Wood, especially oak, is known to emit organic acids,” Bergsten says, and the acetic acid may be from oak that was used to repair the wooden windchests and wind system of the organ in the 1970s.

Developing better conservation strategies is one of the main goals of the project, which is supported by the European Union. By understanding the sources of corrosion, it might be possible to change an organ’s environment to protect it. If not, researchers are also developing protective treatments that could be applied to the surface of a pipe. They expect to test experimental conservation strategies on the Stellwagen organ by 2005.

Sara Pratt
Geotimes contributing writer

Extreme storms as climate warms

Last fall, four hurricanes cruised up Florida and the U.S. East Coast. Across the globe, Japan was hit by 10 typhoons in its worst storm season in decades. To the other extreme, recent droughts are ongoing in the Western United States and Australia.

Aspects of this extreme weather may be related to global climate change, some scientists say: As climate continues to warm, hurricanes and other storm events may increase in intensity, and extreme storms increase in frequency. On the flip side, droughts may become more frequent and severe.

“It’s always possible to have extreme weather events,” says Kevin Trenberth of the National Center for Atmospheric Research (NCAR) in Boulder, Colo. A few large storms can always happen by chance, even in conjunction, he says. However, with hurricanes, “the odds are actually changing,” Trenberth says, “and they’re changing in ways that match models of what’s happening in climate change.”

Scientists have tracked an increase in rainfall over the past few decades. Data over the past century in the United States shows that total precipitation increased by 7 percent, and extremely large storms increased 14 percent, according to Pavel Groisman and co-workers at the National Climatic Data Center in Asheville, N.C. Publishing in the Journal of Hydrometeorology last February, the team noted that most of the increase in precipitation days has happened within the past 30 years.

Climate change impacts do not stop with rainfall, but affect droughts as well. The steady buildup of carbon dioxide from human activity and other factors has added a lot of energy to the climate system, Trenberth says. That energy causes more drying, which pulls more water into the atmosphere in some spots, and then leads to more precipitation in others. “Where it’s not raining, it causes more droughts,” Trenberth says, and “where it is raining, it gathers together and causes flooding.”

Ongoing drought in Australia corresponds to flooding in Peru, scientists say, as does drought in Southeast Asia and parts of Africa, places that normally are wetter during the La Niña part of the El Niño/Southern Oscillation climate cycle. Moreover, Trenberth says, even though the 2002-2003 El Niño was considered moderate, Australia’s drought is one of the most severe on record.

This year’s typhoon season in Japan is the worst since the country started collecting complete records of its storms in 1970, according to Matthias Weber, senior vice president of the U.S. Direct Americas division of Swiss Re, an international reinsurance company. The company “expects the season will last one month longer than usual,” Weber said in a telephone press conference in October. Swiss Re estimates that the damage from the four hurricanes that hit Florida this year will approach $20 to $25 billion, with more than twice as many claims as Hurricane Andrew in 1992.

Some researchers, however, argue that the past climate record is not complete enough to determine whether the shifts are just part of a natural cycle. Several recent studies have compared the recent increase in hurricanes in the United States’ mid-Atlantic region to past periods, particularly the 1920s to the 1960s, indicating a possible cyclic pattern of 25 to 40 years.

With the current state of the science, says Tom Knutson of the National Oceanic and Atmospheric Administration, “we can’t say much about global frequency of hurricanes and typhoons” with changing climate. On the other hand, writing in the Sept. 15 Journal of Climate, Knutson and his co-workers have modeled a gradual increase in hurricane intensity in a warmed climate, amounting to a half-category increase in hurricane level a century from now.

“We can’t say anything about the changes in frequency of hurricanes,” says Trenberth, who also spoke at the October press conference, but “we certainly expect there’s going to be more activity.” The question, he says, is whether there will be more individual thunderstorms, or whether thunderstorms will come together more often to form hurricanes. Hurricanes require just the right environmental conditions to coalesce, in winds that will not blow the storm apart but will allow it to rotate.

“What is clear is that there will be more disturbances — there may be more tropical storms rather than hurricanes,” Trenberth says, and with those storms, heavier rainfall and more damage.

Naomi Lubick

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