Download Global temperature vs. years as extracted from an Antarctic ice core

CS_Ch12_ClimateChange
3/1/2005
4:56 PM
Page 757
Activity 2 Paleoclimates
temperature (°C)
2
Geo Words
0
isotope: one of two or
more kinds of atoms of a
given chemical element
that differ in mass
because of different
numbers of neutrons in
the nucleus of the atoms.
–2
–4
–6
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
–8
years before present
Figure 3 Temperature variation over the past 420,000 years,
relative to the modern surface temperature at Vostok (–55.5°C).
Bubbles of air trapped in the ice contain samples of the atmosphere from the
time when the snow fell. Paleoclimatologists study the oxygen in the water
molecules in the ice.Almost all of the oxygen atoms in the atmosphere are in
two forms, called isotopes.The two isotopes are oxygen-16 (written 16O) and
oxygen-18 (written 18O).They are the same chemically, but they have slightly
different weights. 18O is slightly heavier than 16O.The proportion of these two
isotopes in snow depends on average global temperatures. Snow that falls
during periods of warmer global climate contains a greater proportion of 18O,
and snow that falls during periods of colder global climate contains a smaller
proportion.The ratio of 18O to 16O can be measured very accurately with
special instruments.Another important way of using the glacier ice to estimate
global temperature is to measure the proportions of the two naturally
occurring isotopes of hydrogen: 1H, and 2H (which is called deuterium).
The air bubbles in the ice contain carbon dioxide.The amount of carbon
dioxide in the glacier ice air bubbles depends on the amount of carbon
dioxide in the air at that time.The amount of carbon dioxide in the
atmosphere can be correlated to global temperatures. During times when
the paleoclimate is thought to have been warm, the ice core record shows
relatively higher levels of atmospheric carbon dioxide compared to times of
interpreted colder climate. Measurements of carbon dioxide taken from the
cores give a global picture, because carbon dioxide is uniformly distributed in
the global atmosphere.
A third component of the ice that yields clues to paleoclimates is dust. During
colder climates, winds tend to be stronger.The stronger winds erode more
dust, and the dust is deposited in small quantities over large areas of the Earth.
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