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Spring 2000

Science Bits

Mayfly morphology offers clues to prehistoric barometric pressure

Cornell University geologist John Cisne suggests the fossil record of the common mayfly as a database for estimating the mass and composition of the prehistoric atmosphere. Mayflies little different from their modern descendants first appear in the fossil record 300 million years ago. The size of the forewings provides a record of the density of the air in which they flew.

Swarms of mayflies take to the air in search of a mate by beating their wings rapidly (about 20 to 30 times per second), climbing like a helicopter. At the top of their flight, they pause to drift downward, then resume wing beats to fly back up again.

While watching the mating dance in his back yard, Cisne realized that mayfly morphology responds to air density. Atmospheric pressure would be reflected in the ratio of forewing size to wing muscle size in contemporary and prehistoric mayflies. The force the muscle within the pterothorax delivers to the wings is derived from the length of the pterothorax (the mayfly's two wing-bearing segments), and the force the wings exert on the air is derived from the length of the forewing.

Cisne presented his findings at the December meeting of the American Geophysical Union in San Francisco.

Cornell University

Human health impacts of global climate change

Coroners won't write "death by global warming," but that could be the root cause as millions succumb to disease in an increasingly unhealthy environment, according to ecologist David Pimentel (Cornell University). In a talk at the February meeting of the American Association for the Advancement of Science (AAAS), Pimentel said global climate change is likely to create a favorable climate for disease-causing organisms and food-plant pests.

"Right now the evidence of significant global climate change is minimal, but there are already noticeable increases in human diseases worldwide," said Pimentel. "Most of the increase in disease is due to numerous environmental factors, including infectious microbes, pollution by chemicals and biological wastes, and shortages of food and nutrients. Global warming will only make matters worse."

Pimentel pointed out some ominous trends:

Cornell University

Balancing act? The role of tropical forests in the global carbon budget

Absorption of carbon by new growth in the Amazon rainforest may be sufficient to offset amounts released by deforestation, according to a recent letter to Nature by Richard Houghton (Woods Hole Research Center) and colleagues. The team from Woods Hole, Michigan State University, and the Brazilian Center for Weather Forecasts and Climate Studies (CPTEC) examined annual carbon fluxes in the Brazilian Amazon from deforestation and abandonment of agricultural lands. They estimated an annual flux of about 0.2 petagrams (Pg) of carbon per year between 1989-1998, using satellite data on annual deforestation rates and spatially detailed estimates of deforestation, forest regrowth, and total forest and farmland biomass.

The researchers speculate that logging could contribute another 5-10% to their estimate; in years following drought, fires could double the magnitude of the source. They conclude that the annual source of carbon from land-use change and fire approximately offsets the sink calculated for natural ecosystems in the region. Carbon flux in the Brazilian forest is approximately balanced, but with an interannual variability of 0.2 Pg per year.

Woods Hole Research Center, Michigan State University, Brazilian Center for Weather Forecasts and Climate Studies

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Edited by Carol Rasmussen, carolr@ucar.edu
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Last revised: Thu May 4 14:53:14 MDT 2000