Geoscience Reference
In-Depth Information
global Change and
the greenhouse earth
1
The Greenhouse Effect
through the Ages
It seems that nothing is new under the
sun. The temperature of the Earth's atmo-
sphere, just like the level of the sea, has
varied considerably over time. Most of the
changes have occurred because of varia-
tions in the amount of heat received from
the Sun, which are related to solar activity
and the orientation of the Earth relative to
the Sun.
Atmospheric temperature is also affected
by the concentration of what scientists
have termed greenhouse gases in the at-
mosphere. The greenhouse effect makes life
on Earth possible. As solar radiation warms
the Earth's surface, a portion of the Earth's
atmosphere acts like a greenhouse and re-
tains heat that would otherwise be lost back
to space.
At the time of the dinosaurs, the Earth's
temperature was much warmer. Now, 65
million years after the last dinosaur died,
we have reached a very cool period known
as the Ice Age. Even though we are cur-
rently in an interglacial time, between ad-
vances of the great ice sheets, it is a time
that is too cool for cold-blooded dinosaurs
in most of the places where they previously
lived.
Ever since water accumulated to form the
ocean, not long after the Earth formed 4.6
billion years ago, the level of the sea has
been moving up and down. It was only
in recent millennia, however, that such
changes have affected human beings. For
example, a few miles of the coast of Maine,
fishers have been trawling up spear points,
arrowheads, and other stone implements
from a submerged village site, which was
occupied eight to eleven thousand years
ago. The people who lived at this site, now
under a hundred feet of water, had to pick
up and move inland as the sea level rose
and the shoreline moved past their village.
Almost certainly it wasn't just the gradual
flooding by the rising sea that forced them
to flee. Probably it was a storm or two that
penetrated further inland than usual, or
perhaps their drinking water became too
salty because of the higher sea level. The
effort required to move a prehistoric Native
American village inland is a far cry from
what would be required to relocate today's
New England coastal settlements.
