The carbon dioxide greenhouse - is it effective?: a lab ICT test (teachers’ notes)
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
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.
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.
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.
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 smaller 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.
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)
Activity and preparation
Figure 1 The experimental set up
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