(summary of reliable facts)

CO2 Concentration Over Time

Global Temperature Trends

CO2 Concentration and Temperature: A Cause-and-Effect Relationship?

About CO2 Emissions Trading and Credits



This site is a compilation of information from a number of different sites around the world that are concerned with global warming. This fulfills one of the requirements for an assignment in the subject Air Pollution Control taken in fourth year of the Chemical and Environmental Engineering degree at The University of Queensland.

We have four main goals in composing this site:

1) to find and comment on CO2 concentration trends over time (from most reliable experimental data);
2) to find and comment on average global temperature trends over time;
3) to find and comment on the relationship between these two phenomena; and
4) to summarise and explain how the CO2 emissions trading will work within the framework of the Kyoto Protocol.
Carbon Dioxide Trends over Time
Here is the now famous Keeling curve developed from atmospheric data taken at the Mauna Loa observatory in Hawaii.
 Keeling curve picture
Figure 1: Keeling Curve.
(View data source)

The cyclic variation of CO2 concentration is due to the variation in atmospheric temperature because of changing seasons (from summer to winter and back). During winter the saturation concentration in the oceans increases and hence some of the CO2 in the atmosphere dissolves in the ocean, bringing down the atmospheric concentration.

 CO2 concentration over the last millemmia from the CSIRO
 Figure 2: Ice core data showing CO2 levels over this millennium.
(Taken from the CSIRO site)
As snow falls in cold climates, it traps small amounts of air as it settles on the previous layer of snow. As the successive layers of snow freeze, the small amounts of air are trapped as bubbles in the ice matrix. These bubbles can be used to determine the composition of ambient air at the time of entrapment.  Hence, if an ice core is taken and the bubbles of air analysed, the concentrations of different gases at increasing depth (time) give us a window into the past, in terms of air quality.
The first time drilling into polar ice sheets was accomplished was in 1956 in northwest Greenland ("Site 2") and the first time an ice core reached bedrock was at Camp Century, Greenland in 1966. Since then, ice cores have been taken at a number of sites worldwide, including the Canadian Arctic, North America and Antarctica. For more information and comprehensive data from ice cores, see the NOAA Paleoclimatology Program web page.
Figure 2 was developed from such measurements of air trapped in Antarctic ice, at the Cape Grim Baseline Air Pollution Station. In pre-industrial times the CO2 concentration in the atmosphere fluctuated around 280 ppm. By the 19th century the levels of CO2 started to increase due to the heavy use of coal during the Industrial Revolution and by the 1990s the CO2 level exceeded 350 ppm. This figure plainly illustrates the effect industrial times have had on the composition of the earth's atmosphere.
It has been stated that CO2 levels are now higher than they have ever been in the past 160,000 years (CSIRO site). Findings of this type have been questioned by some investigators who scrutinized some "early accurate analyses" and found the pre-industrial atmospheric CO2 concentrations to be many times larger than the present value (up to 2450 ppm). This must be qualified by saying that the overwhelming majority of data browsed (what is presented here is but a summary) shows that atmospheric CO2 concentration has increased since pre-industrial times and is presently higher than it has been in 160,000 years. These dissenting investigators also go on to criticise the measurement procedure for ice core data and atmospheric CO2 concentrations and say that currently the measurements are not representative of the true concentrations. For more information on this controversial view, click here. Over the time period spanned in the Keeling curve, it can be seen (Figure 3) that the two sets of data agree quite well.
Figure 3: CO2 concentration from various sources.
Global Temperature Change over Time
It is well known that global surface temperatures have been increased through the centuries. We can see in Figure 4 that  from 1850 until today there was an increase in surface temperatures.
Figure 4: Global temperature trends.
(US EPA Global Warming site.)

Figure 4 shows the change in temperature relative to the average of 1850-1870 for the surface temperatures and 1979-89 for the satellite temperatures.

The determination of average global temperatures is quite a complex process; these are based on meteorological data received over the Global Telecommunications System (GTS) for land areas and from an array of ships and buoys that collect sea surface temperature data.  The averaging process is quite complex since the amount of data collected is massive and effort is required to ensure that the data is representative (one controversial issue is the effect of cities on regional temperatures).  There is a great deal of interest in improving the temperature data collection system, because this is seen as  limiting the accuracy of climatic modelling and simulation.  Currently there are several initiatives in place to improve the collection of temperature data and other relevant climatic information.

Although it is well documented that global surface temperatures have been increasing, there is some doubt whether the atmospheric temperature is rising as well. This is demonstrated by the satellite data. The satellite data only spans 1979-89 and does not yet show a conclusive trend, e.g., an upward or downward change in temperature. There are a number of reasons why this data does not show a trend ranging from the data series being too short to errors associated with cyclic variations and use of new technology. This shows that there still is a lot about global climate that is unknown.

Correlations Between CO2 Concentration and Global Temperature
 Is there a cause-and-effect relationship between the increasing CO2 concentration and the apparent increase in global temperatures? It can be seen in Figure 5 that the local (Antarctic) temperature change closely parallels the change in CO2 concentration over the past 160,000 years.

Figure 5: Temperature vs. CO2 Concentration Trends
(Taken from the US EPA web site; see above)
Such a correlation may suggest an affirmative answer to this question. However, there are many different phenomena at play here. What do the experts have to say on this contentious issue? Well, being sufficiently ambiguous to cover themselves, they came up with the following statement:
"The balance of evidence suggests a discernible human influence on global climate"
This statement and much of what follows was sourced from Intergovernmental Panel on Climate Change (IPCC) Working Group I at
When it comes to light how much uncertainty is involved with the global climate mechanism, it becomes clear how difficult it is to make some conclusive statement about the relationship between these two variables and that this vague statement is indeed a rather large step. The IPCC state that any human-induced effect on the global climate will be layered on top of the "noise" of the natural climate variability. This variability depends on two factors: (a)  internal fluctuations, and (b) external causes (such as solar variability or volcanic eruptions). One of the biggest problems is determining the difference between the natural variability and the effect of human influence. There is also uncertainty in key factors such as the magnitude and patterns of long-term natural variability and the time-evolving pattern of forcing by and response to changes in concentrations of greenhouse gases and aerosols and land surface changes.

The IPCC have developed a model that predicts future increases in temperature if the current trends continue. This model is dependent on a number of assumptions concerning population and economic growth, technological changes, energy availability and fuel use during the period 1990-2100. They showed the results for three scenarios using different "climate sensitivities", a low, medium and high value. The predicted increase in global temperature over this interval is as follows:
    Low: ~ 1oC
    Medium: ~ 2oC
    High: ~ 3.5oC.

Figure 6 is a graphical representation of the outcomes of IPCC's modelling work.

Figure 6: Projections to the year 2100.
Basically, the scientific community is missing a large amount of important information that will give a conclusive answer to the questions posed above and it may be some time before this information becomes available. Nevertheless, without knowing the whole story and with the current information, the IPCC statement may be sufficiently disconcerting to warrant international action.

CO2 Emissions Trading
Greenhouse gas emissions are on the rise and the concentration of CO2 and other thermally active gases in the atmosphere is increasing, as previously illustrated.  There is evidence to suggest that if emissions continue unchecked, global warming and climate change to a significant level will result.  The potential  consequences are very serious, from ice cap melting and sea level increases to widespread climatic change and loss of biodiversity - particularly regarding sensitive species.  To attempt to exercise some control over this threat, several types of policy instruments have been offered for consideration, for example, carbon taxes, subsidies for the use of non-fossil fuels, etc.  Many of these are directed toward national emissions reductions to fulfill the requirements of the Kyoto Protocol.  Global scale reductions in greenhouse gas emissions must be the aim of policies and practices to achieve abatement of the potential impacts of global warming.

On global scale, emissions trading has been proposed to reduce CO2 emissions (and other greenhouse active gases such as CH4, etc.) to levels set by the Kyoto Protocol. For Australia the aim is to reduce output in the year 2010 to 108% of the 1990 levels.  Although the details of the emissions trading scheme have not yet been finalised a meeting in November 1998 will determine this the proposal appears to have support.

The use of this type of scheme to reduce air pollution has already been successful, as demonstrated in the USA with SO2 emissions trading.  The aim is to decide the level of emissions that ensures sustainable growth, while slowing the pollution processes.  Thus, the use of emissions trading, rather than determining the final price of consumables through increased costs of production (say, by adding taxes to the costs of production), will determine the level of production by the level of pollution that a company/country will be permitted to emit.

There are two key steps in the implementation of the emissions trading scheme:
    1) the level of emissions permitted for each country, and
    2) the issuing of permits to each country and from there to the relevant industries.

Some companies will not need their quota of permits and would thus be able to sell or trade these unused permits to the more polluting companies.  This may occur nationally, within an industrial sector, or across countries over industrial sectors.

Problems that may arise in such emissions trading scheme:
    -determination of quotas for each country
    -selection of industrial sectors to be included in the scheme
    -infrastructure of the governing body for this scheme and the initial cost to set up the scheme
    -monitoring and enforcement of emissions limits
    -changes in the wealth of countries as they purchase more
    -technological repercussions for countries that have little means to become more environmentally
            friendly while at the same time having the means to purchase more permits
    -value changes in the cost of purchasing permits as new technology creates less pollution.

There are of course more problems than those mentioned here and some are more serious than others.  A common concern, voiced mainly by those who are advocates of a tax base system, is that the focus would be placed onto the obtaining and selling of credits.  This will reduce emphasis on the need to develop new, cleaner technology and upon actually reducing the emissions themselves.

As with all major worldwide policy changes, the final decision will ultimately be based more on political motivation and power than upon the desire to actually protect and preserve the environment, although this may have been the initial contributing factor.  It is very difficult to put into place a policy that does not further disadvantage struggling economies.

The implementation of an emissions credit system would be very politically motivated in that the effects would be not immediately felt by the consuming public (ie the voters) who are usually very quick to jump upon the environmental bandwagon but are not so quick when possible solutions will hit them directly in the hip pocket.  The trading system will make the cost not so obvious as a tax base system and would give the illusion that the price of energy will not be affected.

The web sites cited here give a rundown of the driving forces behind the decisions on new initiatives and point out not only the possible benefits but also the probable costs and problems associated with the implementation of a worldwide solution.  The most common point made is that there is no easy or quick solution to this global problem.  This is also pointed out by the fact that often the most  attractive option to the public and the bureaucrats is not the most economic or environmentally sound decision.
    The National Consumer Coalition
    Intergovernmental Panel on Climate Change (IPCC)

The above mentioned sites provide an analysis of the proposed emissions credit trading system and other policy instruments, either in use or proposed, for the control of greenhouse gas emissions.
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Any comments/queries/questions:
Contact     Benjamin McMahon <>
                      Ceinwen Hooper <>,
                      Christine Bierhuizen <>,
                      Grant Horton <>,
                      Nantarat Jungvimutiphun <>

(slightly edited by, 10/15/98)