CLIMATE SCEPTICISM

“All scientists must be sceptics”

Is human activity the cause of climate change? The debate is far from closed. © Shutterstock/Trance Drumer
Is human activity the cause of climate change? The debate is far from closed.
© Shutterstock/Trance Drumer

Measurements of CO2 quantities released into the atmosphere are taken just about everywhere in the world, using different methods. Tower rising to 35 metres in the forêt de Barbeau (FR) to measure carbon and water flows between a forest ecosystem and the atmosphere. © CNRS Photothèque/Jean-Yves Pontailler
Tower rising to 35 metres in the forêt de Barbeau (FR) to measure carbon and water flows between a forest ecosystem and the atmosphere.
© CNRS Photothèque/Jean-Yves Pontailler

Seawater samples taken from the Mediterranean by the EPOCA project to improve our understanding of ocean acidification. Oceans absorb CO2 emissions of human activity and this results in an acidification of the waters. © CNRS Photothèque/John Pusceddu
Seawater samples taken from the Mediterranean by the EPOCA project to improve our understanding of ocean acidification. Oceans absorb CO2 emissions of human activity and this results in an acidification of the waters.
© CNRS Photothèque/John Pusceddu

Instruments fitted to a kite to measure temperature, wind and CO2 quantities at a height of between 100 and 200 metres. Carried out in Benin, this was part of the Amma (African Monsoon Multidisciplinary Analysis) campaign. © CNRS Photothèque/Claude Delhaye
Instruments fitted to a kite to measure temperature, wind and CO2 quantities at a height of between 100 and 200 metres. Carried out in Benin, this was part of the Amma (African Monsoon Multidisciplinary Analysis) campaign.
© CNRS Photothèque/Claude Delhaye

As the IPCC scientists meet to assess and synthesise the studies enabling us to refine our knowledge of climate change, voices are being raised to question their conclusions.

In science, a majority view never passes as a truth. While most climatology experts subscribe to the general view of the IPCC (International Panel on Climate Change) that human activities are very probably the cause of dangerous global warming, it is a thesis refuted regularly by the so-called ‘climate sceptics’. Lacking an expert knowledge of climatology, most mortals feel powerless in the face of the contradictory arguments. Certain sections of the media, more interested in generating controversy than in informing, add to the confusion.

If we set aside those defending vested interests – using disinformation strategies reminiscent of those adopted by the tobacco giants in the 1980s – and those who see the IPCC as no more than the armed wing of a global politicoecologist conspiracy, we are left with the no doubt sincere sceptics who back up their views with scientific arguments.

Although the arguments take many forms, it is possible to roughly group the sceptics into two camps: those who deny or play down the anthropic nature of global warming, and those who contest its seriousness. The former put forward elements to show that greenhouse gas emissions originating in human activity bear very little if any responsibility for the temperature rises recorded since the mid-20th century. They attribute the rise to natural factors. The second group and its members are not necessarily distinct from the former, and dispute the scientific bases of the future scenarios predicted as resulting from global warming.

What then are their arguments in opposing the opinions of the vast majority of climate experts? It is the sheer complexity of terrestrial systems and their relations with the universe that are the starting point for most of the questions and uncertainties that can still surround the origin and the consequences of present global warming.

The sun as motor for warming

The argument most often put forward to refute the human origin of global warming relates to Earth’s position in relation to the sun and the latter’s activity. Throughout time, it is the intensity of solar activity, the pattern of Earth’s orbit around the sun and our planet’s inclination on this orbit that have governed temperatures. “Over 800 000 years, if we set aside the past 200 years, we see effectively that it is natural factors, such as very gradual changes in the earth’s orbit and the position of the earth on this orbit, that triggered climate changes in the past,” admits Jean-Pascal van Ypersele, Vice-Chair of the IPCC and a climatologist at the Catholic University of Louvain (BE). “But while these parameters vary over very vast expanses of time, they are not enough to explain the sharp rise in temperatures seen since the industrial revolution. You must not mix up very different time scales.”(1)

Also, while CO2 was certainly not the sole causal factor at the outset, this gas is believed to have had an amplifying effect on the consequences of changes to the distribution and total quantity of solar energy available on the earth’s surface. “Astronomical factors are the point of departure, and it is perfectly probable that the slight climate changes caused by these fluctuations did affect the carbon cycle that in its turn influenced past climates.”

The chicken or the egg?

This brings us to another sensitive point in the debate: the relationship between the concentration of CO2 in the atmosphere and temperature variations. While most climatologists say that an increased CO2 concentration in the atmosphere causes a temperature rise on Earth, some scientists – and they have graphs to back them up – stress that over geological time it is temperature rises that trigger increased CO2 concentrations rather than the reverse. “After a temperature rise caused by astronomical factors, the oceans heat up and are less able to absorb atmospheric CO2. It is a law of chemistry: CO2 dissolves better in cold water than in warm water. So a greater proportion of CO2 will remain in the atmosphere.”

So temperature does indeed influence the CO2 concentration. “Sceptics are right in saying that in the time scales of the past CO2 concentrations followed temperature rises. But once there is a certain build up, the CO2 reinforces the natural greenhouse effect and boosts the warming effect. Increasing the thickness of the CO2 layer in the atmosphere is like putting another blanket on your bed, it makes you even hotter!”

Tipping the balance

Thus, on closer inspection, relations between astronomical factors, temperature and atmospheric CO2 concentration as highlighted by the climate sceptics on one hand and by the ‘climate convinced’ on the other do not seem so diametrically opposed. The key question is therefore what impact the greenhouse gases emitted by man have on the complex terrestrial systems. Here too opinions are divided, some believing the impact insignificant and others very significant indeed.

“The CO2 concentration in the atmosphere is negligible compared with that of water vapour, which is the principal greenhouse gas, and natural CO2 emissions are much greater than those of human activities,” is the regular argument of the sceptics. The greenhouse effect is most certainly a natural phenomenon that makes life possible on Earth. Without it, the average temperature on the earth’s surface would be -18°C rather than +15°C. “Water vapour is indeed the principal greenhouse gas. But the problem is not the greenhouse effect as such but rather its intensification that is well documented and that has been measured by satellite readings over the past 40 years. It is this intensification that is unquestionably due to human activity. Analyses of the isotopic composition of atmospheric CO2 prove that the cause of the increase in CO2 in the atmosphere is the burning of fossil fuels.”

It is nevertheless true that natural CO2 emissions are much greater than those originating in human activities. “During a presentation on the carbon cycle to the oil federation in Belgium, in 1997, one climatologist mentioned that flows of carbon of natural origin amount to around 200 billion tonnes a year, compared with 8 billion tonnes of human origin. He therefore regarded it as ridiculous to attack this 4 % represented by anthropic emissions.” But it is all a question of balance. “What he did not say is that natural systems recycle their emissions, in particular through photosynthesis.” These systems therefore absorb as much carbon dioxide as they emit. “It is a delicate balance and if you add anthropic CO2 on one side, then that balance is tipped uncontrollably”. What is more, we are now witnessing mass deforestation that, by reducing the absorption capacity, is further throwing the whole system off balance.

Slamming the door on the IPCC

The climate models(2) on which the IPCC bases its forecasts are also a subject of debate. Are they reliable? Most sceptics consider that we have insufficient knowledge of the parameters that influence the earth’s climate to draw any conclusions. “There is never certainty in science, but the climate models are not mere statistical extrapolations, contrary to what some people claim.” Based on wellestablished physical, chemical and biological laws, the models must first be able to simulate the present climate. The next stage is to check that they are also able to reproduce climates of the past. “That allows us to validate the tool against climate observations dating back hundreds, thousands, or even hundreds of thousands of years, carried out using ice cores in particular. We can then use the models not to predict the future climate, which is impossible, but to make projections.” To judge from the models, these projections vary greatly depending on the future greenhouse gas emission scenarios.

Martin Durkin’s documentary The Great Global Warming Swindle presents scientists who left the IPCC due to their disagreement with the projections of the reports submitted to the political decision-makers. Climatology experts who turn their backs on their colleagues are indeed likely to sow doubts. “Despite being a group of intergovernmental experts, the process of drawing up the reports is very independent. The authors write the texts on the basis of scientific literature and they are submitted to three cycles of rereading, by experts and by governments.” Each comment regarding a line or paragraph is noted in a table and the authors subsequently indicate their response to them. Rereaders then check that the authors have given an honest appraisal of each comment. In the interests of transparency the tables are accessible to everybody at the IPCC site.

“A report represents the work of hundreds of authors and then about 2 500 experts are involved in the rereadings. That at a given moment some will be unhappy – and this has nothing to do with them being good scientists or not – as they are unable to gain acceptance for their own ideas without them being challenged by certain aspects of the literature or by the comments of others, is inevitable.”

When the debate gets heated…

A falling out among experts? In any event, the debate has at times been surprisingly vicious. Some sceptics talk of the ‘blinkered thinking’ of the IPCC while they themselves are sometimes described as ‘negationists’ or ‘revisionists’. The way certain media and many blogs have dramatised the controversy has also helped create a Manichaean vision of the situation as if it were essentially a matter of faith. In the face of such loud and discordant voices the general public no longer knows how to take the current hot and cold climatology debate – forgetting perhaps also that doubt is an inextricable part of the search for truth. “All scientists have the duty to be sceptic. I do not see why some should have the monopoly on scepticism.”

The economic, political and social implications are of course monumental. If the influence of human activities on climate are negligible then a great deal of effort risks being made for nothing – although those who are seeking alternatives to the inevitable exhaustion of fossil fuels remain vital for our energy future. If, on the other hand, the anthropic factor is in the process of permanently upsetting a fragile natural balance, to do nothing to ease the burden and prepare for the consequences would amount to guilty negligence in regard to future generations.

Audrey Binet, Jean-Pierre Geets

  1. Unless otherwise stated, all quotes are from Jean-Pascal van Ypersele.
  2. See the article “The tools of diagnosis”in this issue.

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A thousand years of climate in Europe

Extraction d’une carotte de glace réalisée en Antarctique dans le cadre du programme EPICA. © CNRS Photothèque/IPEV/Claude Delhaye
Extraction d’une carotte de glace réalisée en Antarctique dans le cadre du programme EPICA.
© CNRS Photothèque/IPEV/Claude Delhaye

The aim of the Millennium European Climate project, launched under the Sixth Framework Programme, is to determine whether present climate changes exceed the natural variability of the European climate as observed over the past millennium. Researchers from the 40 universities and research institutes working on the project have pooled their knowledge in various fields to try and reconstitute the European climates of the past. “It is a multidisciplinary project that uses different approaches such as the analysis of historical archives, tree rings, lake sediments, ice cores and models,” explains Rob Wilson, a palaeoclimatologist at St Andrews University in Scotland (UK). “Each approach shows its strengths and its weaknesses, and we are using the strengths of each type of data to establish a history of Europe’s climate over the past thousand years,” he continues.

Once the data have been collected and analysed they are compared with the results of models. “If these two independent sources of information concur, that not only permits a better understanding of past climate changes but also allows us to identify the factors that dominate these changes for the different periods,” explains the researcher. As the Millennium European Climate project runs until June 2010 the final results are not yet available although preliminary analyses made at European level to date “are globally in line with the IPCC’s conclusions,” explains Rob Wilson.

137.44.8.181/millennium


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