The carbon dioxide greenhouse - is it effective?:
a lab ICT test (teachers’ notes)
Level
This exercise relates to the following sections of the English National Curriculum
English National Curriculum reference 3.3.2i
English National Curriculum reference 3.2.5a
English National Curriculum reference 3.4.5a
English National Curriculum reference 4.2.5b
English National Curriculum reference 4.2.5c
English National Curriculum reference 4.3.2q
Topic
This activity aims to teach students about the thermal properties of carbon dioxide –
the properties that make it a greenhouse gas.
Description
The activity consists of a demonstration in which a data logger is used to record the
changing temperature of air and of carbon dioxide in plastic bottles as they are
heated using electric lamps, and then allowed to cool. If a data logger is not
available, then thermometers (0 -100C range) can be used instead and monitored
by pupils. The activity allows students to compare the thermal properties of carbon
dioxide with those of air, and can be extended to compare water vapour as well. The
gas which absorbs the most heat (infrared radiation) is the most effective greenhouse
gas as in the atmosphere it would absorb more infrared coming from the Earth’s
surface.
Context
Increasing atmospheric carbon dioxide levels and associated global warming are
often in the news – for example, coverage of an international environment summit
(like that held in Johannesburg in 2002) or of local initiatives to cut carbon dioxide
emissions (like ‘Walk to School Week’), or energy-saving initiatives in school. So,
pupils are probably quite familiar with the main issues at stake in the global warming
debate such as where the excess carbon dioxide in the atmosphere comes from,
what might be done to reduce emissions, and that the climatic consequences for
Earth could be devastating. However, it is difficult to understand quite why a
colourless, odourless gas like carbon dioxide should be such a villain. It is abundant
in the air, plants need it to photosynthesise and we breathe it out – how can it be so
damaging to have large amounts of it in the atmosphere? This activity demonstrates
the invisible, thermal properties of carbon dioxide which are what makes it into such
an effective greenhouse gas and thus contributes greatly to global warming.
Teaching points
Since the Industrial Revolution various industrial processes, including the combustion
of fossil fuels, have led to a build-up of greenhouse gases in the atmosphere, which
is considered by many scientists to be linked to an increase in the Earth’s average
temperature. Since 1896 it has been known that the gases carbon dioxide, methane
and nitrous oxide (dinitrogen oxide) help to stop the Sun’s infrared radiation being
transmitted straight back into space again once it has been re-radiated by the Earth’s
surface.
THE INSTITUTE OF BIOLOGY
Much of the Sun’s radiation arrives as the Earth’s surface as light radiation. There
much of it is absorbed and re-transmitted as infrared (heat) radiation. By letting most
of the Sun’s light radiation through, and only letting a smaler amount of the resultant
infrared radiation out again, these gases help to maintain the relatively warm
temperatures that allow the oceans to exist and life to flourish on Earth. Because
they act in a similar way to the glass panes of a greenhouse (ie letting in more light
radiation from the Sun than they let infrared radiation out), they have been
nicknamed ‘greenhouse gases’. So we need our greenhouse around the Earth to
allow life to survive here. The problem is that human activities have disrupted the
natural balance, pumping more carbon dioxide into the atmosphere than there would
be naturally: levels have been raised measurably over the last century. What will be
the effect on the Earth of increasing the amount of carbon dioxide in the
atmosphere? An enhanced greenhouse effect will probably lead to elevated global
temperatures (a trend that may have already begun). This can lead to major climatic
changes such as a change in rainfall patterns, changes in ocean circulation patterns,
warming in some areas, dramatic cooling in others, rising sea levels and coastal
flooding, due to melting ice sheets and thermal expansion of seawater. All of these
will have serious implications for agricultural productivity.
Apparatus
Data logger connected to a PC
Two external temperature probes or thermometers (0C-100C range) if data loggers
and PC are not available
Two 2-litre plastic pop bottles
Two clamp stands, bosses and clamps
Carbon dioxide eg from a Soda Stream
Two heat lamps or flexible spot lights (at least 60 W)
Plasticine™
Safety

Do not place the light bulbs too close to the plastic bottles as they will melt.
Activity and preparation
1. Prepare plastic pop bottles by removing the labels and drilling holes in the
tops big enough to allow the temperature probes or thermometers to pass
through
2. Set up clamp stands and heat lamps as shown in Figure 1.
3. Fill one of the bottles with carbon dioxide, screw the top on (with temperature
probe / thermometer in place) and plug any gaps with Plasticine™.
4. Prepare the other bottle full of air by screwing on the top (with temperature
probe / thermometer in place) and plug any gaps with Plasticine™.
5. Monitor the temperatures of both bottles until they are approximately the
same. At this point switch on the heat lamps and start the recording.
6. After 20 minutes switch the heat lamps off but continue recording the
temperatures for a further 20 minutes
7. Plot a graph of temperature against time for each bottle and compare the two
results.
THE INSTITUTE OF BIOLOGY
Figure 1 The experimental set up
Typical results
Even over a small time period such as 20 minutes we are still able to get a difference
of 4C in temperature between the two samples, the carbon dioxide warming more
and faster than the air, see Figure 2. Students may not be impressed with such a
small temperature difference in the laboratory. However it should be stressed that
scientists are in general agreement that an average increase of just 2C across the
planet could have catastrophic effects on crop production and cause sea levels to
increase significantly resulting in major flooding.
Figure 2 Typical results
THE INSTITUTE OF BIOLOGY