Environmental Engineering Reference
In-Depth Information
Gas trapped in bubbles in each layer can be directly
analyzed to determine the amount of CO
in the atmos-
phere at the time the ice was laid down. The temperature
can be found by looking at the ratio of two stable isotopes
of oxygen,
O and
O, in the water that formed the ice.
The heavier
O amounts to only about
% of the
oxygen in the air. Because of the difference in their mass,
the two forms behave slightly differently on condensing
into water from the vapor phase, or when evaporating
from the liquid. From the measured ratio of the two the
temperature can be determined with precision.
Figure
.
.
shows the temperature and CO
data revealed by the
Vostok ice core.
The cores show a fascinating story of repeated ice ages
that happened roughly every
years. They are
triggered by changes in the shape of the Earth
'
s orbit
from circular to slightly elliptical (
-year period),
the wobble of the poles around the axis of rotation
(
-year period) and the tilt of the Earth
'
s axis
(
-year period). The main effect is from the change
in the shape of the orbit, but the other two can move the
times of temperature minima and maxima around a bit.
During the entire
-year record of the cores, the
temperature relative to today varied from a high of
C
þ
F), while the greenhouse
gas concentration varied from a high of
F) to a low of
C(
(
þ
-
-
ppm to a low
of
ppm. Carbon dioxide was at
ppm at the start of
the industrial age and is now at
ppm, higher than it
has been for
years.
isotopeevidence.html
is a good source explaining how this works.
