CEE 1331 Lab 7: Global Warming
CEE 1331 Lab #7: Global Warming and the Greenhouse Effect
The Greenhouse Effect: Energy from the Sun is the primary driver of the Earth’s climate
system. Energy travels from the Sun through space as electromagnetic radiation in the
form of electromagnetic waves with a wide range of wavelengths from the very small
gamma rays to the relatively large radio waves. However, the heat energy that drives
Earth’s climate system is only a narrow spectrum of relatively short wavelengths in this
electromagnetic spectrum. The important incoming radiation for Earth is mainly visible
light, which has relatively short wavelengths and is not only used to heat the Earth but is
also utilized by plants, algae, and other organisms to drive photosynthesis.
Because Earth gains heat from the Sun and has a temperature above absolute zero (-273°C,
or 0K), Earth constantly emits heat to its surroundings. Because the temperature of Earth
(~ 15°C) is much lower than the temperature of the Sun (~5,500°C) , the energy emitted
by Earth to its atmosphere has a longer wavelength than the incoming visible radiation from
the Sun. This outgoing radiation is therefore known as longwave radiation.
Some gases – known as greenhouse gases - absorb the longwave radiation emitted by
Earth and reradiate this energy in all directions, providing additional warming to the
atmosphere and Earth’s surface. This greenhouse effect is what makes Earth habitable;
without it, Earth’s surface temperature would be on average 33°C cooler (-18°C or 0°F)
which means the Earth would freeze solid from Pole to Pole. Clearly the greenhouse effect
is essential for life as we know it on Earth, although too much of a ‘good’ thing can also
have serious repercussions.
The two most abundant gases in Earth’s atmosphere, nitrogen (N 2) and oxygen (O2), make
up nearly 99% of all the air in the atmosphere, but neither behave as greenhouse gases.
Several far less abundant gases, however, are important greenhouse gases on Earth. These
gases include carbon dioxide (CO2), water vapor* (H2O), methane (CH4), Ozone (O3),
nitrous oxide (N2O) and halocarbons (e.g., chlorofluorocarbons, CFCs).
Of all of these, carbon dioxide is the principal driver of global temperature. Carbon dioxide
is naturally released into the atmosphere from volcanic eruptions, decomposing organic
matter, disintegration of some rocks (i.e., limestone), respiration of plants and animals and
people, as well as outgassing by the world’s oceans.
Carbon dioxide can be taken out of the atmosphere by dissolving in the world’s oceans
where some sea critters can then extract it from the water and use it to create their hard
shells. Marine algae (phytoplankton) can also take CO2 out of the atmosphere for
photosynthesis. When these sea critters and plants eventually die, they sink to the bottom
of the sea taking with them the carbon that was extracted from the atmosphere.
Carbon dioxide is also consistently removed from the atmosphere by land plants during the
process of photosynthesis. During the warmer months when plants are growing, they take
CO2 out of the atmosphere and release O2 in return. This causes CO2 levels to drop in the
hemisphere where the plants are growing. During the colder months, when plants go
dormant, CO2 levels tend to increase once again.
CEE 1331 Lab 7: Global Warming
These natural processes where CO2 is released and absorbed have been approximately in
balance with one another for thousands of years. This means that the amount of CO2
released into the atmosphere has been roughly equal to the amount of CO2 taken out of
the atmosphere every year leading to a stable global average temperature.
However, this balance has been upset in recent decades by the burning of so-called fossil
fuels: coal, oil, and natural gas. These materials, made mostly from carbon, have been
buried deep inside the Earth for millions of years. But modern civilization has extracted
this carbon from the ground and has been burning it for energy in relatively large
quantities since the Industrial Revolution, starting around the year 1750 and increasing
substantially since the 1960s. And whenever carbon, C, is burned, it chemically joins with
oxygen, O2, in the atmosphere to form carbon dioxide, CO2.
This relatively new source of atmospheric carbon – which had been safely sequestered in
the Earth’s crust for millions of years – has been reintroduced into the Earth’s atmosphere
by human activity where natural processes are no longer able to remove it at fast enough
rates. Thus, the balance between the release and the removal of CO2 in the atmosphere
is no longer being maintained.
The chemistry of Earth’s atmosphere has been thrown out of balance with the influx of
billions of tons of carbon dioxide every year into the atmosphere. For over a hundred
years, there has been growing concern that the enhanced greenhouse effect brought
about by these rapidly increasing levels of carbon dioxide could lead to more heat energy
being added into the world’s weather patterns. This would lead to major climate change
resulting in more extreme and dangerous weather events such as unprecedented heat
waves and droughts alongside never-seen-before flooding events, partially due to more
intense hurricanes and typhoons around the world. And with ice sheets and glaciers on
land melting into the sea, global sea levels would rise threatening to inundate coastal
cities displacing hundreds of millions of people in the not-too-distance future.
The following lab procedure will allow you to use verified data to identify the
correlation between atmospheric CO2 levels and global average temperatures
and to use this knowledge to project what may happen to the world’s climate
system by the year 2100.
*A Note on Water Vapor: Water vapor (H2O) is by far the largest contributor to the
greenhouse effect. The direct impact of human activity on the levels of water vapor in
the atmosphere is primarily linked to (a) irrigation for agriculture, and (b) natural gas
(CH4) emissions. CH4 combines with oxygen in the stratosphere, converting to CO2 and
H2O. However, observational data indicate that human activity results in a ≤1% change in
atmospheric water vapor content. Thus, the direct effect that humans have on water
vapor content is significantly smaller than the direct effect humans have on CO 2 content in
the atmosphere. Also, it should be pointed out that a water vapor molecule tends to stay
in the atmosphere less than two weeks before it rains out of a cloud, whereas a CO 2
molecule – once released into the atmosphere - can stay in the atmosphere for hundreds
of years before being removed by natural processes!
CEE 1331 Lab 7: Global Warming
PART I
In this part of the lab, we will be investigating how CO2 levels have been changing over the past
several decades as recorded by CO2-measuring instruments in both the Northern and Southern
Hemisphere.
Go to the following website:
https://gml.noaa.gov/dv/iadv/index.php
Perform the following tasks to create a time series graph of atmospheric CO2 levels from the
Mauna Loa, Hawaii CO2 data collection site from 1969 to 2023:
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Click on the link labeled CARBON CYCLE GASES in the upper right.
Select TIME SERIES from the dropdown menu.
Under Data Type choose FLASK SAMPLES (if not already selected for you)
Under Time Span, select SOME-A SUBSET OF THE AVAILABLE DATA
Under START YEAR choose 1969 (if not already selected for you)
Under END YEAR choose 2024 (if not already selected for you)
Click SUBMIT
You will note that the year the CO2 concentration was measured is labeled on the horizontal axis
of the graph. The CO2 concentration level is labeled on the vertical axis and is measured in units
of µmol/mole which is the same thing as parts per million (ppm). The graph starts at 320 ppm
and extends to over 420 ppm in an interval of 5 ppm represented by the horizontal tick marks.
Analyze the graph you created and answer the following questions:
1) Describe the overall TREND of the graph of CO2 levels since 1969. Be specific!
2) Analyzing air bubbles trapped in glacial ice for over 10,000 years prior to the 19th Century,
we know that CO2 levels around the world did not change very much during this time. So, what
is responsible for the TREND in the graph that you observe for the years 1969 to 2023?
3) What is the meaning of the ORANGE color for the data points at the tail end of your graph?
Perform the following tasks to create a graph of CO2 concentration since 2020 by performing the
following tasks:
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Under Time Span, select SOME-A SUBSET OF THE AVAILABLE DATA
Under START YEAR choose 2020
Under END YEAR choose 2024
Click SUBMIT
CEE 1331 Lab 7: Global Warming
Note the little tick marks on the horizontal axis of your graph. These now represent the months
of the year starting with January where the year 2020 is plotted and going through December,
which is identified with the little tick mark right before the year labeled 2021.
Also note the tick marks in the CO2 concentration level labeled on the vertical axis. Each tick
mark on the vertical axis now represents 1 µmol/mole, which is the same thing as 1 part per
million, or ppm. And so, for example, between the labeled values of 410 and 415 we see four
tick marks. The first one after 410 would therefore be 411 ppm, followed by 412 ppm, followed
by 413 ppm, and then followed by 414 ppm.
Keeping in mind that Mauna Loa is located in Hawaii in the Northern Hemisphere at
approximately 19.5°N latitude and knowing the relationship between plant photosynthesis
and CO2 mentioned earlier in this document, answer the following questions:
4) Explain why the CO2 levels go up and down during each year in the graph.
5) What was the lowest CO2 concentration level since 2020? In what month/year did this occur.
6) What was the highest CO2 concentration level (using ALL data points for consideration) since
2020? In what month/year did this occur. Why do you think this particular CO2 level might just
be an error?
7) Do you expect the CO2 levels in your graph to trend UP or DOWN for the next few months
going into early 2025 and WHY?
And now let’s go to the Southern Hemisphere and observe carbon dioxide levels from that part
of the world where the seasons are reversed and where the population is much less than what
is found in the Northern Hemisphere.
To analyze CO2 data from a location in the southern hemisphere click on the small link labeled
SITE SELECTION in the upper right corner of your computer display or click the following
link, https://gml.noaa.gov/dv/iadv/index.php
Now choose the red circle located to the SE of South Africa in the southern Indian Ocean. This is
Crozet Island located at about 46.5° S latitude.
Click on the CARBON CYCLE GASES link on the right side of your display and choose TIME
SERIES from the dropdown menu. Then click on the blue SUBMIT button at the left bottom on
the screen that will appear to plot CO2 levels at this location from 1991 to 2024.
8) What is the overall TREND in CO2 levels at this southern hemisphere location? Be specific!
CEE 1331 Lab 7: Global Warming
9) How does the magnitude (i.e., maximum values) of CO2 levels at Crozet Island compare to
the magnitude (i.e., maximum values) of the CO2 levels at Mauna Loa in the Northern
Hemisphere you saw earlier?
10) Knowing the more abundant land areas and the higher population in the N.H. compared to
the S.H., what could be the possible explanation for the difference in the magnitude of CO2 levels
at these two locations?
While staying on this webpage for Crozet Island, perform the following:
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Under Time Span, select SOME-A SUBSET OF THE AVAILABLE DATA
Under START YEAR choose 2020
Under END YEAR choose 2024
Click SUBMIT
11) Once again you will observe an up-and-down nature to the data points, BUT there is a
noticeable difference when compared to the Mauna Loa data. What is the MAIN difference
between the “sawtooth” pattern in the Northern Hemisphere compared to the “sawtooth” pattern
in the Southern Hemisphere AND what is the explanation for this difference? (Hint: examine the
months that the max and min values occur)
12) If we could use Mauna Loa as representative of the Northern Hemisphere and Crozet Island
as representative of the Southern Hemisphere, what would be the average CO2 levels for the
Earth as of May 1, 2024?
CEE 1331 Lab 7: Global Warming
PART II
Atmospheric carbon dioxide levels can be determined by analyzing the contents of trapped air
bubbles in ice cores drilled from the ice sheets of Greenland and Antarctica. Carbon dioxide
levels since 1958 have been more directly measured by actual scientific air sampling
instruments. The following table is a blend of these two data sources showing AVERAGE
carbon dioxide levels for the Northern Hemisphere measured in parts per million (ppm) since the
year 1764.
Year
1764
CO2
Concentration
(ppm)
270
1791
Year
1943
CO2
Concentration
(ppm)
308
Year
2010
CO2
Concentration
(ppm)
390
280
1953
313
2011
392
1816
284
1961
318
2012
394
1839
283
1964
320
2013
396
1843
287
1967
322
2014
399
1847
287
1970
326
2015
401
1854
288
1973
330
2016
404
1869
289
1976
331
2017
406
1874
289
1979
337
2018
408
1878
290
1982
341
2019
410
1887
292
1985
346
2020
412
1899
296
1988
351
2021
415
1903
295
1991
355
2022
418
1905
297
1994
359
2023
421
1909
299
1997
363
1915
300
2000
369
1921
302
2003
376
1927
306
2006
382
1935
307
2008
386
CEE 1331 Lab 7: Global Warming
In this part of the lab, you will be investigating whether there is a correlation between the amount
of carbon dioxide (CO2) in the air and the global average temperature.
13) Using the Excel spreadsheet containing the carbon dioxide levels from 1764 to 2023, plot the
CO2 concentration levels (in ppm) as a function of time. You should plot and label the Carbon
Dioxide Levels (ppm) on the vertical axis (y-axis) and the CALENDAR YEAR across the
horizontal axis (x-axis). Label your graph, “Carbon Dioxide Levels from 1764 – 2023. Please
make sure your graph extends out to include the year 2050 (as described below), the reason
for which will soon become obvious.
To make accurate estimates of CO2 levels, it is necessary to make some adjustments to the
default way that Excel is displaying your graph. To make these adjustments, complete the
following tasks:
a) Click on the vertical axis numbers to highlight them, and then right click and choose
FORMAT AXIS. Under the AXIS OPTION, set the MINIMUM value to 260 and the
MAXIMUM value to 450. Also, set the MAJOR units to 10.
b) Click on the horizontal axis numbers to highlight them, and then right click and choose
FORMAT AXIS. Under the AXIS OPTION, set the MINIMUM value to the year 1760 and the
MAXIMUM value to the year 2050. Also, set the MAJOR units to 10.
Please Note: You will have to make your graph larger in order to make your graph more
readable. Simply click on your graph display window and drag the corners until the graph is big
enough so that you can easily interpret the data.
Compare your graph of atmospheric CO2 to the graph on the next page which shows the Global
Average Surface Temperature Anomalies from 1880 to 2020. The graph on the next page shows
how the annual average temperature for the Earth has fluctuated above and below the long-term
20th Century average temperature. These departures from normal are called temperature
anomalies. Any year with a temperature plot above the “0” line would be above the 20th Century
average and thus be a positive anomaly, and anything below the “0” line would be below the 20th
Century average and thus be considered a negative anomaly.
14) In what decade did both CO2 levels AND Global Average Temperatures rapidly and
consistently increase? (Keep in mind that just because two variables are correlated with one
another does not necessarily mean one caused the other. Other evidence is needed to make that
determination.)
CEE 1331 Lab 7: Global Warming
Global Climate Models (GCMs) suggest that if the atmospheric CO2 levels reach 450 ppm, this
would result in an average global temperature that would be 2°C warmer than pre-industrial
times (before the year 1750) – a time when global temperatures were relatively stable with no
well-defined trends.
Global Climate Models (GCMs) also predict that a 2°C temperature rise since preindustrial
times means major NEGATIVE impacts from climate change are likely to occur. This could lead
to more extreme weather events such as more powerful hurricanes and typhoons as well as more
intense droughts and heat waves around the planet and as much as a foot or more of ocean water
spilling into the world’s coastlines by 2100 as a result of sea level rise, including some of the
largest cities in the world like New York and Beijing.
15) Using ONLY the last 24 years as a guide (2000 – 2023), what year would you estimate the
Earth’s atmosphere will reach 450 ppm?
To do this, mentally extrapolate the last 24 years (from 2000 – 2023) of your graph to the top of
your chart and find the year corresponding to the point where your extrapolated line reaches
450 ppm at the top of your graph.
IMPORTANT: DO NOT draw a best fit line through ALL of your data points from 1764 to the
present year. If you do, you will NOT get an accurate estimate of future CO2 levels because the
graph from 1764 to 2022 is a curve rather than a straight line.
CEE 1331 Lab 7: Global Warming
PART III
Examine the following figure which shows CO2 Concentration Levels in the atmosphere as well
as the Global Average Temperature anomaly - the departure from normal which is indicated by
the 0 value on the vertical axis - during the last 430,000 years. The values on these graphs were
derived by using proxy data which we discuss in the lecture portion of the course.
Current day is on the right-hand side of the graph where the label “0” is located. As you go right
to left, you go back in time to 430,000 years ago. Therefore, as you read the graphs going from
left to right, you approach the present day.
16) Is there a correlation between carbon dioxide levels and the global temperature anomaly for
the last 430,000 years? If so, what is it?
17) Does there appear to be a cyclical pattern in the CO2 concentration in the atmosphere? In
other words, do the peaks in CO2 concentration levels appear at roughly equal intervals of time?
If so, what is the time interval of the cycle?
18) Note the current level of CO2 in the atmosphere (the vertical green line in the far-right side
of the graph) and compare it to the levels recorded for the last 430,000 years. Based on the
observed CO2 levels in the Earth’s atmosphere today AND the rate it is increasing, can you find
any other time in this graph where CO2 levels were increasing as fast as they are today? How
will the Earth’s temperature in the year 2100 compare to anything in the last 430,000 years?
CEE 1331 Lab 7: Global Warming
PART IV
The main energy source for heating the Earth is, of course, the sun, and the average amount of
energy from the sun intercepted by the Earth is about 238 Watts per square meter, or 238 W/m2
or 238 Wm-2. You can think of it this way: for every square meter on Earth, you would have
more energy than necessary to power two 100-Watt lightbulbs just by using the Sun as an energy
source. This solar radiation warms the Earth.
And as we have seen, greenhouse gases like CO2 also warm the Earth by absorbing longwave
radiation emitted by the Earth and re-emitting some of it back down to the surface, making the
planet warmer than it would otherwise be. And thus, greenhouse gases can be considered another
energy source other than the Sun, delivering additional heat to the planet.
We can consider the warming effect (i.e., radiative forcing) of increasing CO2 levels in the
Earth’s atmosphere and converting this additional energy into units of radiation energy per
square meter (Wm-2) by using the following equation:
Greenhouse Energy = 5.35 x ln [ Current CO2 Concentration / Initial CO2 Concentration ]
where "ln" is the natural logarithm function.
The above equation tells us how much additional energy is delivered to the Earth when CO2
levels increase from some initial concentration level to present day levels.
19) How much additional energy (in Wm-2) has been provided to the Earth by CO2 since 1750
when CO2 levels were near 280 ppm but are now closer to 423 ppm?
CO2 levels have increased nearly 50% since 1750. But there are other greenhouse gases in the
atmosphere that contribute to global warming: methane, ozone, nitrogen dioxide, and
chlorofluorocarbons. If we wanted to find the additional energy provided by each of these
greenhouse gases, we could use a similar equation like the one above for each of the gases by
using the CURRENT and INITIAL concentrations of each of the gases.
However, there is a simpler way. It turns out that these other greenhouse gases can be converted
into CO2 mathematically to yield an "equivalent" CO2 concentration in the atmosphere. In other
words, we can convert the warming effect of methane, ozone, nitrogen dioxide, and
chlorofluorocarbons by converting their warming effect to what it would be if they all acted like
carbon dioxide. By doing this we can use the same equation.
It turns out that when all these gases are considered, they provide an equivalent of an additional
70% (instead of just 50% mentioned just a moment ago) of CO2 since 1750.
20) Taking methane, ozone, nitrogen dioxide, and chlorofluorocarbons into account, what would
be the equivalent CO2 concentration that is present in the atmosphere today?
21) How much additional greenhouse energy (in Wm-2) has been provided by CO2, methane,
ozone, nitrogen dioxide, and chlorofluorocarbons since 1750?
CEE 1331 Lab 7: Global Warming
Global Climate Models (GCM) predict that CO2 levels could rise to near 1000 ppm by the end
of this century if the burning of fossil fuels continues to increase at a rapid rate worldwide.
(Could be as low as 540 ppm if a reduction in fossil fuel burning is achieved)
22) How much additional greenhouse energy (radiative forcing) will be provided by this amount
of CO2 (i.e., 1000 ppm) by the year 2100 compared to 1750? How much of this radiative forcing
comes from just the years between now and 2100? (Ignore the contributions from other
greenhouse gases for this calculation)
Research from the world’s climate scientists suggests that an increase of average global
temperatures by just 2°C since preindustrial times could lead to catastrophic climate change.
GCMs reveal that for every increase in 1 Watt per square meter of absorbed energy in the Earth’s
climate system, there is a corresponding increase of 0.34 °C in the global average temperature.
Currently the average global temperature is 15°C which is already an increase of about 1.2°C
since preindustrial times (~1750).
23) How much will the global average temperature increase by the year 2100 compared to today
if CO2 levels rise to 1000 ppm by 2100? (Ignore the contributions from other greenhouse gases
for this calculation)
24) Will the increase in temperature from CO2 alone that you calculated in question #23 exceed
the 2°C rise threshold?
25) Do a quick Google search and identify at least 4 ways human civilization or even individual
people could reduce the amount of CO2 in the atmosphere by the year 2100 which may prevent
or at least mitigate the most severe impacts from global warming and climate change.