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Summer 2002

Science Bits

Will floodgates save Venice from rising sea levels?

The Italian government recently decided to move forward with planning for mobile floodgates to mitigate rising seas in Venice. However, debate about the plan continues among university and laboratory scientists, as reflected in two articles in the 14 May issue of Eos.
The plan involves construction of 79 gates at three lagoon inlets. When waters rise about 110 centimeters above a predetermined level, air will be injected into the hollow gates, causing them to rise and blocking Adriatic Sea water from entering the lagoon. The floodgates will take an estimated eight years and cost $2.6 billion to construct.

Some critics of the plan, such as Paolo Antonio Pirazzoli of France’s National Center for Scientific Research (CNRS), are skeptical as to whether the gates will actually prevent flooding. According to Pirazzoli, the gates’ design is based on outdated predictions of sea-level change, using a scenario that differs by nearly 26 centimeters from more recent estimates put forth by the Intergovernmental Panel on Climate Change. Pirazzoli also asserts that the designers did not consider sea-level rise associated with land subsidence or increased water levels associated with extended rainy or windy periods.

Once sea-level rise exceeds 31 centimeters, says Pirazzoli, the system would become obsolete and would need to be replaced with watertight gates. He recommends other techniques, such as raising street-level elevations, and awaiting further assessment of sea-level rise to find "an updated, wise solution, more able to cope with foreseeable sea-level change."

In the same issue of Eos, three researchers at the Massachusetts Institute of Technology provide a comment on Pirazzoli’s views. Rafael Bras, Donald Harleman, and Paola Rizzoli, who worked on the design and assessment of the Venice floodgate plan, argue that the gates will prevent major flooding even if overall sea levels rise as much as 50 centimeters. Furthermore, they add, the groundwater removal that caused much of the subsidence of Venice’s islands ended in the 1970s. Bras and his colleagues argue that the cost of doing nothing may be greater than the cost of the current plan as flooding increases. If sea levels rise more than expected, the gates could remain closed more often, in effect serving as permanent barriers.

National Center for Scientific Research, France
Massachusetts Institute of Technology

Kawasaki disease: a climate connection?

The leading cause of acquired heart disease in U.S. children may be related to weather and climate patterns, according to a study led by Jane Burns (School of Medicine, University of California, San Diego). The project teamed epidemiologists and pediatric experts from California and Japan with researchers at NOAA’s Climate Diagnostics Center. Each year Kawasaki disease affects about 6,000 children in Japan and about 15 out of every 100,000 children under the age of five in the United States. No viral or bacterial factor has been identified. There is some evidence for a genetic predisposition, but the cause of Kawasaki disease is unknown.

Although the seasonality of KD in many regions has been recognized for over two decades, the first systematic study of a KD-climate association was not completed until the late 1990s. In San Diego County, a peak in KD cases was consistently noted in late winter, the region’s coolest and wettest season. The local incidence of KD was found to be inversely associated with average monthly temperature and positively associated with average monthly precipitation.

Analyses from northern California and northern and southern Japan showed a similar seasonal link; in each location, the disease was most prevalent in late winter and early spring and least common in the late summer and early autumn. The researchers zeroed in on possible shorter-term weather factors by removing the monthly averages and studying the anomalies in temperature and precipitation that remained.

For both Japan and California, distinct circulation patterns at the 700-mb level (roughly

3 kilometers) tended to develop 10 to 14 days before a wintertime outbreak of Kawasaki disease. In Japan, the favored pattern was a high-pressure center at 700 mb that developed to the northwest and shifted east, gradually bringing in cool marine air. In the preferred California regime, anomalous low pressure to the northwest favored a moist Pacific flow.

Although California sees fewer cases of Kawasaki disease in summer than in winter, its summer episodes are associated with high pressure at 700 mb rather than a moist pattern. "California’s Mediterranean climate regime is one that very rarely receives precipitation [in summer]," the authors note, "so other elements such as clouds, particulates, and perhaps fog in areas that have a marine exposure could possibly be involved."

Rice University
NOAA Space Environment Center
University of California, Berkeley
University of Iowa

Calculating the geologic side of global warming

A team of Michigan and Canadian researchers has found that over the past half-century, the rocks of Earth’s continental crust have warmed significantly, similar to the warming of the oceans, atmosphere, and ice reported by other investigators.

"Our findings remove any last doubt that this is anything other than a global phenomenon," says Henry Pollack, University of Michigan professor of geological sciences. Pollock collaborated on the work with UM assistant research scientist Shaopeng Huang, UM graduate student Jason Smerdon, and Hugo Beltrami (St. Francis Xavier University). The researchers reported their work in the 15 April issue of Geophysical Research Letters.

Continental rock covers almost 30% of Earth’s surface. The team led by Pollack determined how much that rock has warmed in recent centuries by lowering sensitive thermometers into holes drilled into formations on every continent but Antarctica. As rocks at the surface absorb heat from the atmosphere, the warming travels slowly downward into subsurface rocks, leaving a distinct signature. Short-term daily or seasonal variations penetrate only a few meters, but temperature changes that take place over hundreds of years are preserved in deeper rock.

The researchers’ calculations, based on data from 616 boreholes, found evidence of an increase in the heat content of the continents over the past 500 years, with more than half of that heat gain occurring during the 20th century and nearly one-third of it since 1950. Pollock’s team estimates the total amount of heat added from the atmosphere to Earth’s crust at 9.1 x 1021 joules, with an uncertainty of about 10% in either direction due to variations in the thermal conductivity of various rocks.

In a 2001 paper, oceanographer Sydney Levitus (NOAA) and colleagues estimated the total amounts of heat stored by oceans, atmosphere, and ice over the last 50 years. When the new figures from Pollock’s team are combined with the previous calculations from the Levitus paper, the overall partitioning of added heat is roughly 86% into the oceans, 4% into rock, 6% into ice, and 3% into the atmosphere (the total is less than 100% due to rounding).

"The ocean has clearly seen the largest increase in heat content during this period," note the researchers, "but we suggest here that the lithosphere is an important constituent that should be considered in the accounting of the total heat gain within the global climate system."

University of Michigan
St. Francis Xavier University

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Edited by Bob Henson, bhenson@ucar.edu
Prepared for the Web by Carlye Calvin
Last revised: Mon June 10 16:42:17 MST 2002