Spring 2000
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Science Bits
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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:
- Today, infectious disease causes approximately 37% of all deaths
worldwide, but the estimated number of deaths due to a variety of
environmental factors is higher and still growing. "Environmental diseases"
are attributed especially to organic and chemical pollutants, including smoke
from wood fuel and tobacco.
- More than 3 billion people currently are malnourished--the largest
number and proportion in human history--and the number increases every year.
Malnutrition increases susceptibility to infectious and environmental
diseases.
- A population increase to 12 billion in the next 50 years (based on
current growth rates) will exacerbate the spread of disease globally, Pimentel
said. Densely crowded urban environments, especially those without adequate
sanitation and nutrition, are sources of disease epidemics. Dengue
fever, spread by the Aedes aegypti mosquito, is expanding
rapidly in crowded tropical cities. Some think that with global
warming, this mosquito and others will spread north, transporting
dengue and other diseases from the tropics.
- Waterborne diseases--already accounting for 90% of deaths from
infectious disease in developing countries--will become more prevalent in a
warmer, more polluted, and more crowded planet. For example, only eight of
India's 3,120 towns and cities have full wastewater treatment facilities.
Hundreds of millions of people in India and other developing countries are
forced to use untreated water for drinking, bathing, and cooking.
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,
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Prepared for the Web by Jacque Marshall
Last revised: Thu May 4 14:53:14 MDT 2000