Most Saturday mornings of the winter months find a group of high school students, parents, and teachers at the Princeton Plasma Physics Laboratory listening to a "Science on Saturday" lecture. Two successive recent Saturdays were devoted to scientific aspects of the future of life on Earth: "Global Warming" and "Maintaining Biodiversity While Protecting Crops." Science on Saturday series explores future life on Earth
Speaking about "Global Warming," on 31 January 1998, was Dr. Isaac Held, of Princeton University's Geophysical Fluid Dynamics Laboratory, who recalled his first introduction to the topic by an orientation lecture when he was a college freshman. He particularly recalled how the professor was concerned about the Earth a hundred years from now while he was more concerned about getting through the next week.
Atmospheric carbon dioxide is known to affect the radiative equilibrium between Earth and sun, which in turn determines Earth's temperature, currently making Earth 33oC warmer (15oC rather than -18oC). Held showed how this makes Earth's infrared radiation into outer space appear to come from the altitude in the atmosphere at which the temperature has decreased to -18oC. As Earth's temperature increases, as it has since 1970, Held pointed out, this altitude in Earth's atmosphere from which outward infrared radiation appears to originate will become higher.
Held noted that our records of atmospheric carbon dioxide are historically more reliable than those of temperature. Prior to current measurements at Mauna Loa, which show an increase from 315 ppmv (parts per million by volume) in 1958 to 355 ppmv in 1994, we know the concentration of atmospheric carbon dioxide from ice cores, while temperature records date back only to about 1850.
Held also pointed out that carbon dioxide and other atmospheric molecules absorb and re-emit Earth's infrared radiation to produce global warming because of the vibration and charge separation of their moleucles. The only atmospheric constituents not fitting this description are the two most prevalent -- molecules of nitrogen and oxygen (whose bonds are nonpolar) -- and the trace amounts of inert gases.
Held showed a series of composite satellite images showing infrared emissions throughout the world for December 1987-January 1988 and lamented that a lack of present satellites would preclude providing the same images today. Today, he noted, we must rely extensively on computer modeling, which predicts temperature, wind, pressure, density, humidity, and cloudiness for cells in the atmosphere from rules for their interaction with each other and their evolution in time. In addition to incorporating the effect of global warming from greenhouse gases, climate models also include solar reflectance from aerosols. Held observed that two models which have correctly matched Earth's recent past thermal history predict unprecedented rates of temperature change -- an increase of 14oC at the North Pole when atmospheric concentration quadruples its preindustrial value of 280 ppmv, but a decrease at the South Pole. Also predicted in the early 21st century is a reduction in overturning of ocean currents in the Atlantic Ocean (northward surface currents and southward deep currents).
As the temperature of Earth continues to warm, its population continues to increase, and more food is needed to feed its people. Dr. Laura Whatley of American Cyanamid spoke on 7 February 1998 about "Maintaining Biodiversity While Protecting Crops."
Biodiversity, she said, is a lot of living things in the same place. The more the number of species, the more stable the ecosystem. But, she asked, how can we maintain biodiversity while preserving crops?
One important answer to this question, she noted, was integrated pest management, which draws upon all pest management tools available in the way that wreaks the least ecological damage, by attacking pests at their weak points. (She added that only pest management is possible, not control or eradication.) Some of these tools are physical or mechanical -- e.g., hoes, which remove weeds that compete with plants for sunlight -- while others are biological (natural enemies, choice of variety, and even humans themselves) or chemical, some of them occurring naturally -- e.g., pyrethrium (from the chrysanthemum), sulfur, pheromones (in Japanese beetle and gypsy moth traps).
Other chemical tools are synthetic, which are regulated by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Under FIFRA and EPA (Environmental Protection Agency) regulations and guidelines, Whatley pointed out that companies typically spend $50 million over ten years to perform up to 120 studies -- in chemistry, toxicology, residues, metabolism, nontarget effects, and environmental fate.
Focusing on the role of biotechnology in introducing resistant plants and modified organisms, Whatley observed that the BT gene in plants produces a toxin to "worms." Another agent she reported under investigation is the baculovirus, which occurs naturally and affects only certain insects (not the praying mantis, honeybee, or ladybug beetle). Insects have an alkaline midgut, she said (in contrast with acid digestion in humans), which is attacked by the baculovirus. American Cyanamid has investigated baculoviruses targeted against the tobacco budworm and cabbage looper. Removing part of the egt gene of the baculovirus enables it to kill 15-30% faster, she stated, but even better performance is needed. An answer to this quest for better performance has come from adding the AaIT gene from a scorpion; it increases the kill rate by 40-60%, she said, without affecting the host range.
Using synthetic chemical pesticides indiscriminately harms biodiversity, but could we maintain biodiversity and protect crops without any synthetic pesticides? Farming without synthetic pesticides, also known as "organic" farming, was all the human race knew prior to the development of synthetic pesticides; but Whatley suggested that, because its yield is lower, it would be unlikely to be able to feed an ever-increasing world population.
(Editor's Note: Information about the work of the Geophysical Fluid Dynamics Laboratory can be obtained on the World Wide Web at http://www.gfdl.gov)
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