Contrasting viewpoints

Contrasting viewpoints

The basic outline of the scientific case that human emissions of greenhouse gases affect the planet’s average temperature is well known. The ‘other side’ of the story disputes some or all aspects of the mainstream scientific case.

There are many ideas put forward in the media and online in blogs about climate change. Different interpretations can arise from different analysis of the data, from the use of completely different data (which may or may not be accepted by others in the debate), or from alternative hypotheses to account for observations and behaviours of natural systems. This is inevitable in seeking to understand, and predict the behaviour of complex systems. Contrasting views can also come from misunderstandings of the science (whether wilful or not), or from outright rejection of evidence and logic, and its replacement with conspiracy theories, suspicion and emotion.

Some of the alternative views about climate change are discussed here. The Parliamentary Library is not a scientific research organisation and must rely on information from elsewhere. In order to ensure the validity of this information, the Library bases its publications and analysis on peer-reviewed journals or other reputable sources where possible. There is far more evidence supporting anthropogenic global warming in these journals than against it. By itself, this fact does not make anthropogenic global warming ‘correct’ —it must stand or fall on its scientific merits and not on the number of journal articles or the number of scientists supporting it. However, it suggests that there is considerable scientific consensus on the main planks of the case of human-induced warming. It also means that more material on this ‘consensus’ view is available and suitable for the Parliamentary Library to use than material that contradicts it.

In this part of our web site, information is taken from, and linked to, sources that are not always verified. The Parliamentary Library does not endorse all the content of all websites referred to.

Any scientific advance involves uncertainty, disagreements, dispute and change as evidence and observations are accumulated and incorporated into theory. Scepticism is an important part of the scientific process; results, observations and interpretations are regularly duplicated, revised, disputed or discarded. See the Parliamentary Library’s web page on ‘Scientific uncertainties’ for more information.

Not all ‘greenhouse sceptics’, as they are sometimes dubbed, are in the same camp. There is a great diversity of views, which vary considerably in their degree of acceptance of the scientific consensus. The more extreme doubters reject outright virtually all scientific evidence, and some maintain that there is a globally co-ordinated conspiracy to fabricate the notion of climate change and of human effects on the atmosphere. The more ‘moderate’ sceptics may accept the evidence for warming, but dispute the fact that humans are responsible for most or for any of the measured changes. Others point to disagreements between scientists and to the inherent uncertainties that exist in any scientific case.

Some of the alternative views about climate change are examined here. However, it should be stressed that among scientists in the relevant disciplines, the overwhelming majority agree on the basic outline of the case that the Earth is warming, and that emissions of CO2 and other ‘greenhouse gases’ from the activity of industrial humans are the likeliest cause of most of this warming. Of course, much dispute exists about some of the details.

Alternative views that go against the basic outline of the scientific case for climate change are rare among climate scientists; they occur more often from scientists in other disciplines, and more often still from non-scientists and from the media.


Here, contrasting views will be presented by posing ten questions or statements and then addressing each one:

1) Are human activities responsible for increased CO2?
2) Both temperature and CO2 concentrations have always varied on Earth, and so climate change is nothing new and probably quite natural.
3) Carbon is natural, and carbon dioxide gas is essential to life on Earth.
4) CO2 is not a pollutant; it is perfectly natural and indeed beneficial.
5) Water vapour is responsible for global warming. CO2 does cause some warming, but only a very small degree.
6) Are global temperatures really rising?
7) Global Temperature may have risen in the 20th century, but it has recently decreased.
8) CO2 may not be the cause of the warming.
9) Effects of the sun.
10) What about Earth’s orbital changes and axis tilt?

There appears to be no serious dispute over the measured increase in atmospheric CARBON DIOXIDE (CO2) concentrations in the lower atmosphere. The measurements, from many locations around the world, are relatively straightforward to carry out and seem to be accepted by all sides. For example, the following graph shows the CO2 increase measured by CSIRO at the Cape Grim station in Tasmania.

CSIRO carbon dioxide data


The Parliamentary Library has been unable to find any reputable data that disputes this.

1) Are human activities responsible for increased CO2?

There is no doubt that if a substance containing carbon is burned in air, then oxides of carbon (mainly CO2 and a variable amount of CO) will be formed and released into the air. The combustion of carbon fuels releases carbon dioxide. However, carbon dioxide can also be emitted from volcanoes, and can be absorbed or emitted (depending on the conditions) from the soil and the oceans. In addition, the biological process of photosynthesis absorbs CO2 and the process of respiration releases it. As there are therefore several factors affecting overall CO2 concentration, is the measured increase in atmospheric carbon dioxide entirely or even partially due to human causes?

Data from air bubbles trapped and sealed many thousands of years ago in ice, and other evidence, show fairly conclusively that the concentration of CO2 has varied often in the past before there was any human influence. Usually, large changes in CO2 concentration have correlated with temperature changes. It has been debated for some time whether increases in global average temperature in the geological past were caused by increased atmosphere CO2 or whether it was the other way round – temperature increased for some other reason, which then caused CO2 to be released. Given that the solubility of CO2 in water decreases with increasing temperature, then it seems possible that warmer conditions could cause a release of CO2 from the oceans. Changes to soil temperature can also affect the net flux of CO2 into and out of soil. It is also possible that an unknown factor caused both CO2 and temperature to change at roughly the same time. And, on top of that, there are feedback effects which complicate the picture: increased temperature causing CO2 release from the oceans, which in turn might cause the temperature to increase further.

It is acknowledged by most scientists in the relevant disciplines that both climate and atmospheric composition changed considerably, but probably slowly, during the geological past before the existence of humans. It has therefore been postulated that such changes in the last 100 years are also natural – i.e. that most of the additional CO2 has sources other than human activity. However, this ignores the fact of the known CO2 release from fuel burning, and therefore requires explaining where that CO2 has gone. It also raises the question of the source of the observed increase in CO2 if it is not from human activity. In the geological past, periods of intense volcanic activity, and outgassing from oceanic ridges, are thought to have been responsible for some periods of CO2 increase but this is not the case now.

2) Both temperature and CO2 concentrations have always varied on Earth, and so climate change is nothing new and probably quite natural.

There is little disagreement in the scientific literature with the first part of this statement. Evidence suggests that throughout the geological past, measured in hundreds of millions of years, there was considerable variation in Earth’s climate. At times, such as the Pliocene, it was much warmer than today, and mangrove swamps occurred at 69° South—which is in Antarctica today, but where southern Australia was located at the time. Equally, there were periods when the Earth was much colder (glacial periods, or ‘ice ages’). Similarly, there is evidence that CO2 concentrations also varied, being much higher than today until the evolution of large land plants about 400 million years, which caused a considerable decline in the abundance of atmospheric CO2. (See, for example, GEOCARB III: a revised model of atmospheric CO2 over phanerozoic time)

Hsitoric carbon and temperature variance


This graph can be used to argue that average temperature and CO2 concentrations are not closely linked. It appears to show that a global average temperature of about 22°C persisted over hundreds of millions of years despite considerable fluctuations in atmospheric CO2 concentrations. However, many other factors can also affect global temperature over long time periods.

Moving to more recent geological times (the last one million years), Earth has shown regular glacial and interglacial periods. We have only recently, geologically speaking, emerged from an ice age (a glacial period). This occurred about 10,000 years ago, when our modern climate became established. Of course, during an even shorter period – those 10,000 years – there have also been small and more rapid variations in climate.

It is easy to forget, however, that these changes took place over thousands of years. Human civilisation of the last five thousand years has developed during a time of particular climate, and for the moment relies on retaining the characteristics of that climate. Humanity’s advanced civilisation and large population is now much more vulnerable to disturbance by climate change than were our cave-dwelling ancestors.

3) Carbon is natural, and carbon dioxide gas is essential to life on Earth.

All scientists would agree with this statement and there is nothing in the published scientific literature that contradicts it. The carbon element cycles between various ‘compartments’ (the atmosphere, biosphere, rocks, sea floor) and moves between various chemical forms – existing as the gas CO2 when it is in the air, or being incorporated in complex molecules in living organisms, or in rocks such as calcium carbonate.

The gas CO2 is the starting point for photosynthesis, upon which nearly all life on Earth depends. Where disagreement may arise is in the conclusion that sometimes follows. The fact that CO2 is a natural, and indeed an essential, component of the Earth’s atmosphere is sometimes used to suggest that its increasing concentration is harmless. This does not follow. Just because something is ‘good’ does not mean that more of it is better. It all depends on the amount. This leads onto the next alternative view.

4) CO2 is not a pollutant; it is perfectly natural and indeed beneficial.

Pollution depends on how much of a substance is present and where it is. Pollution of natural origin can occur—for example, a volcano releasing toxic compounds into the atmosphere and waterways. The legal question of whether carbon dioxide qualifies as a pollutant is beyond the scope of this analysis, but the fact that CO2 is natural and essential does not mean it cannot be deleterious– in the same way that a natural and essential substance like water can cause flooding if too much accumulates in the wrong place.

Higher concentrations of CO2 in air will stimulate photosynthesis, provided that other factors, such as nitrogen, water and various nutrients are not limiting, and this CO2 fertilisation effect has been detected. Globally, photosynthesis appears to have been responsible for the fact that the measured increase in atmospheric CO2 over the last century is less than the volume of CO2 released by the burning of carbon fuels. Just because increased CO2 in the air stimulates photosynthesis, which removes some of it, does not negate the fact that the remaining gas can cause warming by absorbing heat radiated out from the planet’s surface.

5) Water vapour is responsible for global warming. CO2 does cause some warming, but only a very small degree.

Water vapour is a strong greenhouse gas, as the following figure demonstrates. The dips in the blue line show the wavelengths of the electromagnetic spectrum where various atmospheric gases absorb electromagnetic radiation. Water absorbs more strongly across wider wavebands than CO2. As a result, water is responsible for much of the planet’s ‘natural greenhouse effect.’ However, there has been no demonstrated increase in average water vapour in the atmosphere to account for the measured warming. The water cycle causes water to move in and out of the atmosphere quickly.

Measuring the sprectral expression of carbon dioxide in the solar reflected sprectrum with AVRIS

Source: Measuring the Spectral Expression of Carbon Dioxide in the Solar Reflected Spectrum with AVIRIS

Warmer air is able to hold more moisture than colder air, and it seems likely that a warmer world, on average, will have a faster water cycle of evaporation and precipitation.

The ‘greenhouse’ effects of water vapour vary according to whereabouts in the atmosphere the gas is located. Related to the amount of water vapour is the question of cloud. Clouds can cool the surface, as their bright tops reflect heat and light from the sun. However, the presence of clouds (or water vapour) in the atmosphere at night usually keeps the surface warmer, by preventing the escape of heat from the ground up into space. The overall feedback effects of clouds are one area that it is hard for climate modellers to agree on. There are many views here and it is probably fair to say that the science in this area still needs refining.

6) Are global temperatures really rising?

Most people who argue against anthropogenic climate change accept the temperature record as it is, and dispute the reasons put forward by scientists for why global warming has occurred. However, some doubts have been raised as to whether the average planetary temperature is indeed increasing. The accuracy of the temperature measurements themselves has been questioned.

The temperature record comes from a variety of sources. Meteorological measuring stations on land can be subject to the well-known urban heat island (UHI) effect. This refers to the tendency of urban areas to be warmer than their surroundings because of the dark surfaces of roads and roofs, and the heat emitted from vehicles, factories and buildings. Urban growth during the twentieth century has meant encroachment on measuring stations; re-siting stations further away from the urban zones is possible but any change in location will invalidate a long temperature record.

The stations must either remain where they are and an ‘adjustment’ for urban heat must be applied to their readings, or they are moved – but even with scrupulous care the new location may have local differences in the micro-climate that mean that the new readings after the move are not directly comparable with the ones from before. If the sites remain, the adjustments for UHI – which take into account readings from nearby non-urban areas – can be contentious.

It is telling, however, that if the data from measuring sites within a city centre, a suburb, and a surrounding rural zone are compared, although they give different absolute readings, all show the same upward trend over decades. London provides a good example of this as in the following:

London annual temperature trends

Annual temperature trends for five sites in and around London. Brown and dark blue are urban sites, green are rural. Source: Skeptical Science-Urban Heat Island effect exaggerates warming at

However, the trends shown in London could be explained away by saying that the rural areas are not as rural as they were 30–40 years ago, and hence may contain a greater number of roads, houses and passing vehicles. And the temperature increase in the city centre sites could simply be recording the energy released by a city that may be consuming more energy over time.

It is claimed by some that many US temperature measuring stations do not comply with regulations when it comes to their siting. See This website maintains that 58 per cent of 807 US meteorological stations surveyed were sited within 10 metres of an artificial heat source.

The following illustrations from the website show a well-placed meteorological station in California, with its accompanying temperature record, and a recording station sited incorrectly, also in California, along with its temperature record for the same time period.

However, the Parliamentary Library cannot vouch for the accuracy of this, or be sure if the temperature recordings from such unsuitable sites are actually used in the long-term record that forms part of the claim of global warming. It may well be that the data from a proportion of the many thousands of weather-recording sites is unreliable, which is why claims for global warming must be based on large quantities of data from many places over long periods.

Correctly sited weather recording station with its temperature record:

Well sited weather station

Incorrectly sited weather recording station with its temperature record:

Badly sited weather station


In addition to poor siting, land measurements have been criticised because the recording stations tend to be most numerous in relatively developed countries and in inhabited areas, and therefore are under-represented in many parts of the world.

Temperature measurements of air over the oceans (and of sea surface temperature) have been taken by ships for many decades, but differences in the protocols used have recently come to light.

It has been suggested that the differences in the way in which sea surface temperatures were made can account for part of the drop in the temperature record from the 1940s to the 1970s—meaning that this fall in temperature is actually an artefact. However, there are other reasons proposed for this 30-year fall in the temperature record (increased sulfate aerosols from pollution). Regardless of the detail, the fact that ship measurements might not always have been consistent can be used to argue that the temperature record is not entirely accurate.

Radiosonde balloons are also used to measure air temperature at different places and altitudes as they ascend. They have a longer record than the satellite observations. However, changes in measurement techniques and instrumentation from the 1940s to the present mean that their data is also open to challenge.

Planetary temperature has also been measured by satellites since the 1970s, but some questions remain about the algorithms used to convert the terrestrial radiation detected by the satellite into a temperature at ground level or at a point within the atmosphere. Different research groups have interpreted the raw data in different ways, coming to various conclusions about warming. Most, however, agree that satellite data shows a warming trend over the last 30 years or so but the extent of this warming is subject to disagreement.

In addition, there are ‘proxy’ indicators of warming, such as changes to glaciers and ice caps, and tree growth, as shown by data gathered from analysis of tree rings. Again, the fact that most glaciers are shrinking and that sea ice in many areas is declining can be challenged by findings of some glaciers that are not shrinking, and that, in some areas of Antarctica, some sea ice is increasing. While the Arctic has seen record sea ice loss in 2007, parts of the Antarctic did not. It is thought that the increase in sea ice around Antarctica (excluding the Antarctic Peninsula, where sea ice is decreasing and temperatures are increasing) may be due to changes in atmospheric circulation brought about by the depletion of the ozone layer over Antarctica, which changes the amount of UV radiation reaching the lower atmosphere.

Precipitation (as snow) is also expected to increase over much of Antarctica as a result of the warmer atmosphere being able to hold more water vapour, although so far observations do not unequivocally demonstrate any large change in the ice mass balance of Antarctica as a whole. Moreover, there can be other explanations (for example changes in ocean currents) for the break-up of ice shelves such as Larsen B in the Antarctic. Other scientists, however, argue that the break-up is due to stronger westerly winds that are indirectly brought about by anthropogenic global warming.

With sea ice and ice cap thickness, claims and counter-claims can fly thick and fast according to exactly what is being measured and how, the precise location under study, and how the statistics are interpreted. Ice coverage is not the same as ice thickness; therefore the extent of coverage by sea ice does not reliably indicate whether there has been a net loss or gain of ice. In addition, using only a few years’ worth of data does not give a reliable indicator of a trend. It seems fair to conclude that more knowledge and research, and longer and more reliable data series, are required to unequivocally detect trends and attribute causes. This is the case with all scientific research, however, and the one certainty in science is that 100% certainty is not a realistic goal, and we must be satisfied with probabilities (often of 90% or 95%) that a theory is correct, based on the available evidence.

The media or apologists for both sides of the debate may cherry-pick selective data and findings, without relying on a broader and more accurate picture. Weather is different from climate, and anywhere around the world in a given year new weather ‘records’ are being made and broken. It is just as misleading to point to a 2009 record heatwave in Melbourne as evidence of global warming as it is to use the 2009 record cold and snowfall in United Arab Emirates as evidence of global cooling.

Note also that June 2009 snowfalls in parts of the USA were the first June snow recorded in sixty years. Such happenings are not useful evidence of the long-term trends that would herald climate change or the lack of it. It is rather like using the anecdotal reports of a grandfather who smoked all his life and never got cancer to disprove the link between smoking and lung cancer. The link is based on large studies involving hundreds of thousands of people and is a probabilistic connection, taking no account of individual differences, and therefore not a sure-fire correlation for every individual. That does not, however, invalidate the science behind it.

7) Global Temperature may have risen in the 20th century, but it has recently decreased.

There appears to be considerable evidence to back up that statement, if it refers to air temperatures at the surface. But it must be seen in context, as shown in the graph below, from the Hadley Centre in the UK. It is clear that 1998 – the warmest year ever recorded – is an anomalous baseline from which to calculate a temperature decline.

Global average temperature

Source: Met Office, Hadley Centre UK

Thus, the answer to whether global temperatures are really increasing or decreasing depends on the time scale on which one looks. The global average temperature for 1998 was ‘hot’, partly because of a strong El Nino, whereas the year 1989 was, globally, less remarkable. A trend from 1989 to 1998 would show strong warming. However, the data from the peak of 1998 to 2008 would show little warming.

The next graph shows temperature anomaly in the lower troposphere inferred from satellite data, and calculated by the University of Alabama Huntsville (UAH). Other researchers do not necessarily agree with the UAH calculations.

temperature anomaly in the lower troposphere inferred from satellite data

Source: University of Alabama Huntsville

However, to avoid the misinterpretations arising from cherry-picking certain extreme years (either hot or cold), a linear trend can be more revealing. The following graphs show little cooling (in fact, a slight warming) from 1998 to 2007.

Linear temperature trend

Source: Skeptical Science at

In any case, it is the long-term trend that is of interest, i.e. over several decades. Climate scientists do not suggest that temperature responds directly, instantly and linearly to greenhouse gas emissions. There is a large degree of variability in climate brought about by quasi-periodic changes in atmospheric and oceanic circulations (such as the El Niño-Southern Oscillation) and other natural factors like volcanic eruptions and small changes in output of the sun. See Solar variation and Volcanic eruptions.

8) CO2 may not be the cause of the warming.

In the laboratory it is quite clear that CO2 absorbs radiation of certain wavelengths, and these correspond with some of the wavebands emitted by the Earth. In addition, changes in past temperature and CO2 concentration show a correlation. However, correlation is not causation. Water vapour absorbs far more strongly, across more of the relevant wavelengths than CO2, and is therefore also a powerful greenhouse gas. Whether the increased CO2 concentration in the atmosphere is responsible for the global warming that is thought to have occurred has been challenged on a few occasions.

There would be few, if any, papers published in climate science journals questioning the link between atmospheric CO2 concentrations and warming.

As water is a powerful greenhouse gas, it has often been suggested that its effects should receive more scrutiny. The combustion of carbon-containing substances, as well as releasing CO2, also produces H2O, e.g.

CH4 + 2O2 —› CO2 + 2H2O

Some have questioned why any greenhouse effects of the additional water vapour from fossil fuel burning are usually ignored. The global water cycle, whereby water is exchanged between the oceans, atmosphere and land water bodies, involves time scales that are very rapid compared to CO2 and other greenhouse gases, so the water molecules do not stay in the atmosphere for very long. In addition, the capacity for air to hold water vapour is limited by the atmospheric temperature, which determines the saturation point (after which water vapour will condense and fall as rain or snow). Observations do not demonstrate any clear changes in atmospheric water vapour concentration since pre-industrial times, suggesting that the water added from burning carbon fuels quickly falls out of the atmosphere.

9) Effects of the sun.

This is an area where there are many alternative views, and the science is less certain because we do not have reliable, long-term records of the sun’s behaviour over millions of years. However, if the sun is changing now, we are well placed to detect it, with an array of satellites measuring it, as well as instruments on Earth.

The data clearly shows that the sun’s output of heat is not absolutely constant. It varies very slightly over the short-term (the 11-year solar cycle or sunspot cycle) and over longer periods (as noted above, the Library’s web page on Solar variations discusses this issue). Satellite measurements of total solar irradiance (TSI) give the clearest indication of the short-term variations. The figure below, from NASA, shows years from 1996 to 2008 at the top.

1996 to 2008 soalr irradiance

Source: ESA/NASA SOHO Missions;

The fact that the solar cycle is established means that any direct effects can be accounted for. However, there are other possible solar effects that have been suggested. The sunspot cycle is not always 11 years in length. It varies, and it has been suggested that when the cycle is longer the Earth is cooler. However, such a correlation does not prove causation.

Also of interest are the suggestions relating to changes in cosmic ray density hitting Earth. When the sun is in the more ‘active’ phase of its cycle (with more sunspots and greater total radiation output), its magnetic field is stronger, which deflects cosmic rays away from Earth. Conversely, when in a weaker or quiescent phase, such as it has been since about 2007, the sun’s magnetic field is reduced and more cosmic rays arrive on Earth. In October 2006 Henrik Svensmark showed experimentally that cosmic rays may promote cloud formation in the lower troposphere. Most clouds in that part of the atmosphere would have a net cooling effect, and this mechanism could account for global cooling at times of lower solar.

The cosmic ray idea needs further data and verification but it could prove to be an amplifying effect for the relatively small changes in total solar irradiance, thereby giving a mechanism by which solar variation could effectively account for some global temperature changes. However, if so, then there would presumably be an 11-year cycle in cloudiness and temperature.

Moreover, other authors have shown that Svensmark’s claims about the effect of the sun on Earth’s climate are not as robust as first thought. The following graphs suggests little link between variations in cosmic ray intensity (lower two lines, black and brown) and global temperature (upper two lines, green and purple).

Cosmic rays and surface temperatures


10) What about Earth’s orbital changes and axis tilt?

It is well known that Earth’s orbit does not stay constant over the millennia but varies slightly, and that the tilt of the planet’s axis with respect to the plane of its orbit also wobbles over thousands of years. These two factors can have major effects on climate. There is some evidence to suggest that the passage of ice ages (glacial periods) and warmer spells (interglacials), which are such a well-known feature of the geological record, are partly caused by cycles in Earth’s orbit, as well as by changes in the sun’s luminosity and other astronomical factors. However, the scientific study of astronomy in the last century and, more recently, access to space have demonstrated little significant changes in Earth’s orbit, axis tilt or solar luminosity at the present time. See The earth's orbit.

Further reading:

Catherine Brahic, Buckets to blame for wartime temperature blip, New Scientist, 28 May 2008.

Science News, Antarctic Deep Sea Gets Colder, ScienceDaily, 23 April, 2008.

Science News, Antarctic Ice Shelf Retreats Happened Before, ScienceDaily, 28 February 2005.

Science News, First Direct Evidence That Human Activity Is Linked To Antarctic Ice Shelf Collapse, ScienceDaily, 16 October 2006.

Anna Zacharias, Short life expectancy for RAK snowman, The National, 25 January 2009.

The Royal Society, Misleading argument 4: ’Temperature observations don’t support the theory’.

Skeptical Science, Surface temperature records are unreliable.

Greg Baker, El Niño and the Southern Oscillation Index, Parliamentary Library, 29 September 1997., Cosmic rays and Earth's climate, October 2006.

The Royal Society, Misleading argument 7: ’the climate is actually affected by cosmic rays’.

Paul Damon and Peter Laut, Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data, Eos,Vol. 85, No. 39, 28 September 2004., Taking Cosmic Rays for a spin, 16 October 2006


22 October, 2010

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