Time Machines Into the Past
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Research scientists from around the world are working together to collect and study glacial ice cores. Data from
these ice cores provide one of the most complete records of past climate conditions. Of greatest interest are the
deep cores obtained by drilling programs in Summit, Greenland and Vostok, Antarctica.
Preparing Ice Cores for Analysis
Ice cores reveal the story of Earth's climate in reverse order. The uppermost layers of the core tell the most recent
history, with increasingly deeper layers providing a record of progressively older periods.
Analyses of ice cores offer a direct and detailed record of atmospheric conditions over time. Glacial ice not only
records changes in the climate but also preserves evidence of the causes of those changes. By studying ice cores,
scientists hope to more accurately predict future climate trends.
Temperature Data from the Vostok Ice Core
Scientists can reconstruct a record of temperatures that occurred in the past by analyzing the ratio of oxygen
isotopes trapped within air bubbles in the ice. The graph below shows how the temperature has changed over the
past 165,000 years. The graph shows temperature anomalies—variations in the temperature above or below
Vostok’s present day average temperature of -56ºC.
! Examine the graph carefully to interpret how time is represented along the bottom axis. Look for places on the
graph that represent a warming trend, when the temperatures increased over time, reaching a peak at some
maximum temperature before a cooling trend began.
1. Over the past 165,000 years, how much has the temperature varied above and below the current average
temperature?
! Move your cursor over the peak that occurred around 133,000 years ago to highlight that part of the graph.
Follow the graph from right to left, examining the large-scale temperature changes. (Ignore the smaller peaks and
dips.) Around 145,000 years ago, the temperature began to increase rapidly, reaching a peak about 133,000 years
ago. Then the average temperature decreased fairly steadily, reaching its lowest point around 107,000 years ago.
! Move your cursor over the low temperature dip that occurred around 64,000 years ago to highlight that part of
the graph.
Beginning from a peak around 82,000 years ago, the average temperature started dropping, and it reached a
minimum at 64,000 years. Following this, the temperature increased until it peaked again at around 52,000 years
Identifying Warming and Cooling Periods
Two markers have been placed on the graph. One marks the peak of a strong warming trend at 133,000 years ago,
and the other marks the minimum temperature reached at the end of a cooling trend 64,000 years ago. Carefully
examine the graph and identify a peak that marks the end of another strong warming trend and a dip marking the
end of another strong cooling period.
! Drag the arrows from the tool palette onto the graph to mark these two points. Use another piece of paper to
record the ages of all four marked points.
Carbon Dioxide (CO2)Data from the Vostok Ice Core
Scientists can determine the amount of carbon dioxide that was in the air during different time periods by analyzing
gas bubbles trapped in ice cores. Carbon dioxide is a greenhouse gas that plays a major role in the atmosphere’s
energy balance.
This graph has fewer small peaks and dips than the temperature graph because it was drawn with fewer data
points. Study the graph and identify two obvious points when the level of carbon dioxide in the atmosphere
increased to a major peak and two points when it dropped significantly to a minimum level before rising again.
! Drag the arrows from the tool palette onto the graph to mark these four points. Use another piece of paper to
record the ages of all four marked points.
Compare the timing of the high and low points you labeled on the Temperature and CO2 graphs.
2. Does there appear to be any correlation between the major high and low points on the two graphs?
Explain, using specific examples.
3.
What do the data suggest about the relationship of temperature and the amount of atmospheric carbon
dioxide (CO2)?
4. Which of the two variables, temperature or CO2, appears to have begun rising first?
Temperature and Carbon Dioxide Data from Vostok
Temperature and carbon dioxide data are plotted together on this graph. This makes it easier to compare the two
variables and how they may be related.
! Move your cursor over the graph to highlight the period between 110,000 and 150,000 years ago. Examine the
timing of peaks in temperature and carbon dioxide.
The graph shows that temperature and carbon dioxide levels both started to increase around 144,000 to 146,000
years ago.
5. Which of these two variables appears to have peaked first?
The graphs also indicate temperature and carbon dioxide amounts both peaked around 133,000 to 135,000 years
ago.
6. Which of these two variables appears to have begun dropping first?
! Move your cursor over the graph to highlight the period between 0 and 20,000 years ago.
7. Examine the relationship between temperature and CO2 for the period from 20,000 years ago to the
present. Explain what you observe.
8. Based on your observations, hypothesize about the relationship between temperature and the amount of
CO2 in the atmosphere.
Recent Changes in Atmospheric Carbon Dioxide
Scientists have been precisely measuring the amount of carbon dioxide in the atmosphere since 1958. The results
of these studies are plotted on the graph below. The yearly average CO2 level is represented by the smooth black
line, and seasonal changes appear as small peaks and dips.
9. Based on your observations of CO2 amounts, predict how temperatures changed from 1958 to 2001.
Dust Data from the Vostok Ice Core
Glacial ice cores also provide a record of the amount of dust in the atmosphere, because dust is trapped in layers
of ice after it settles on the surface. Higher quantities of dust, called dust fluxes, are associated with major glacial
periods when parts of the world tended to be very dry and windy. Atmospheric dust results from a specific set of
climate conditions, so it is not considered a cause of climate change. This is different from the cause-and-effect
relationship that appears to exist between the atmospheric CO2 and temperature.
! Move your cursor over the graph to highlight the period between 10,000 and 30,000 years ago.
10. For the period from 10,000 to 30,000 years ago, describe the apparent relationship between temperature
and the amount of dust in the atmosphere.
! Move your cursor over the graph to highlight the period between 50,000 and 70,000 years ago.
11. Do data for the time period of 50,000 to 70,000 years ago support or refute the relationship you stated in
question 10? Explain how.
Predicting Temperature from Dust Data
Data on dust amounts from the Vostok ice core extend about 25,000 years further back in time than CO2 and
temperature data.
! Draw the relationship you observed between temperature and dust levels to draw in your best estimate of the
temperature between 165,000 and 190,000 years ago.