Environmental Engineering Reference
In-Depth Information
oceans; and possible changes in major ocean currents that affect coastal
and national climates.
The effects will differ by region. The tropics and high-latitude regions
will see more rainfall, while temperate regions, many of them already
short of water, will get drier. High latitudes will warm faster than lower
latitudes. On a more local scale, the changes become more complex and
hard to predict.
Effects on Living Organisms
The poleward march of the living has already begun. This will affect
American agriculture in terms of the areas best suited for growing crops.
Economic disruptions are certain to occur as states previously too cool
for certain crops become able to grow them, and states that dominated
the production of certain crops lose their dominance. If needed, genetic
modifi cations of crops will likely be engineered by the agrobiotech com-
panies to mitigate the adverse effects of increased temperature. Weeds
and crop pests will increase with warmer temperatures, but they can be
controlled. Pollinating insects will increase. Overall, agricultural produc-
tivity in the United States as a whole will probably not be seriously
affected.
Many plants and animals are already responding in subtle ways to
local climatic changes. In the 1970s, mosquitoes became one of the fi rst
organisms in which scientists observed genetic changes that might be
attributed to global warming. More recently, scientists reported that the
genetic makeup of organisms ranging from fruit fl ies to birds might also
be responding to climate trends. For example, in 1970, California white-
crowned sparrows sang fast machine-gun trills. Just a few decades later,
the sparrows sang noticeably slower songs because the bird's habitat has
gotten scrubbier, and their melodies have evolved to better penetrate the
thickets.
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Slow songs and low-pitched sounds transmit better through
dense vegetation, whereas high notes carry farther in open environments.
Overall, grassland birds do have faster, shriller songs than those from
leafy surroundings have. Adaptation apparently required no more than
a few decades. Another example is the effect that increased carbon
dioxide in the air has had on the quaking aspen, which has had a 50
percent acceleration in growth in suitably moist climates over the past
fi fty years.
According to the International Union for Conservation of Nature and
Natural Resources, 20 percent of mammals, 30 percent of amphibians,
and 12.5 percent of birds are threatened or endangered. But the Inter-
