Handout on increasing atmospheric CO2
How do we know the amount of CO2 in the atmosphere is rising?
#1) Mauna Loa, Hawaii measurements of
atmospheric CO2
Scientists take direct measurements of the amount
of CO2 in the air using instruments on a tower at
Mauna Loa, Hawaii. The primary site for the Mauna
Loa Observatory and its carbon dioxide sampling
equipment is located at 11,000 ft on the island of
Hawaii. The Weather Bureau founded the
observatory in 1956 to gain access to clean, particlefree air when it could not find a suitable site in the
continental U.S.
In 1974, NOAA instituted a global program of
monitoring carbon dioxide and other atmospheric
gases. The Mauna Loa Observatory installed a new
carbon dioxide analyzer system at that time that operated in parallel with the older 1956 system. The NOAA
and Scripps carbon dioxide analyzers, operating together at Mauna Loa, provide important redundancy of
measurements. The measured CO2 data, shown in ppm or parts per million, is below.
Look at the graph and answer these simple questions:
What was atmospheric CO2 in ppm in 1957?
What was atmospheric CO2 in ppm in 2007?
Here is a more difficult question.
There is an annual pattern to the CO2 measurement. Every year it goes up and down – a wave pattern. Why?
Why isn’t the level of CO2 the same all year long? What would make the amount of CO2 change during the
course of a year?
2) Vostok, Antarctica ice core measures of CO2
Scientists would like to know about the
amount of CO2 in the atmosphere in the
past. Since they cannot use an instrument
to directly measure CO2 from long ago, they
use what are called ‘proxy’ records. One
kind of proxy record is an ice core. An ice
core is a sample core removed from an ice
sheet, for example in Antarctica or
Greenland. As ice forms from the
incremental buildup of annual layers of
snow, lower layers are older than upper, so
extracting an ice core contains ice formed
over a range of years. An ice core has the
accumulation of snow and ice over many
years that have re-crystallized and have
trapped air bubbles from previous time
periods. The composition of the ‘old trapped
air’ in these ice cores provides a picture of
the atmospheric CO2 for times in the distant
past.
Scientists at the Vostok Research Station in Antarctica drilled ice cores into the Antarctic ice sheet that
allowed them to determine the CO2 concentration in the atmosphere over the past 400,000 years. The data is
below.
How to read this data and graph: Today is Year 0. As you go backwards in time, go along the X axis to the right.
Do you see 100,000 years ago? 200,000 years ago? The graph shows CO2 in the atmosphere up to 400,000 years
ago.
Atmospheric CO2levels rise and fall over the long time period of 100s of thousands of years. This change in
CO2 concentration coincides with glacial and interglacial periods. During glacial periods when much of the
globe is covered with ice and snow (an Ice Age), atmospheric CO2 levels are low. When the ice recedes and
the earth warms, more plants cover the land and the ocean waters are warmer, and then there are higher
levels of CO2 in the atmosphere.
If you look at the Vostok ice core data, its possible to say – “Increasing CO2 in the atmosphere is no big deal!!
CO2 concentration has been going up and coming back down for half a million years!!”
Why is this statement incorrect?
Because … In the past 400,000 years, what was the very highest concentration of CO 2 in the atmosphere?
Now, look closely at the data for Year 0. Using the Mauna Loa data or this Vostok ice core data, what is the
concentration of CO2 today?