Summary

The links within this section address a large number of arguments against various aspects of climate change. They discuss why the theories have arisen, and where the evidence now points. I've summarised a few of the most common arguments below, based largely on the New Scientist and Royal Society websites, as I believe these to be more likely to reflect a balanced scientific opinion.

The theories I consider are:

• Not all scientists believe climate change
• Modelling techniques are not reliable, and systems are too complex
• Current changes are insignificant compared to past variations
• The lower atmosphere is cooling
• Parts of the world are cooling, not warming
• Extra-terrestrial influences including cosmic rays are to blame
• The temperature readings used to back up climate change are incorrect

I have included the links to a number of sources at the bottom of this page.

Not all scientists believe climate change

This is definitely true. There are a number of people who publicly doubt that climate change is caused by human intervention, or that the predictions relating to the future changes are accurate. However, even the most vocal, Prof. Lindzen of MIT, does not deny that climate change is occurring.

Indeed the vast majority of scientists, as represented by the IPCC and various national scientific academies have backed the results of the IPCC reports relating human activity to climate change. Academies from 16 countries have explicitly supported the 2001 IPCC report.

A US study in 2001 noted that the IPCC report had accurately reflected the current thinking of the scientific community. In addition, a 2004 review of almost 1000 abstracts containing "global climate change" in the previous 10 years found none that rejected the consensus view.

In summary, although there are many areas of doubt within the explanations of climate change, no scientific evidence has been put forward to contradict the fact that the climate is warming, and the majority of scientists believe that human activity has some bearing on this.

Modelling techniques are not reliable, and systems are too complex

The models used to anticipate climate change do not function stochastically, in that they are driven by starting conditions and assumptions regarding future emmissions and other factors. They are essentially scenario tests for the future climate. In addition these models vary in how they treat the links between various parameters, and the effects of certain elements, notably cloud formation.

The climate is indeed complex, and influenced by many factors in ways that are not well defined, however these models are back-tested to see how well they can pedict past climate change. In addition it is worth making the distinction between weather and climate. Climate refers to the average conditions over wide areas, and has timescales of around 30 years. It is this mean position that the models are attempting to analyse, and hence localised events and fluctuations, relating to more chaotic elements, become less relevant.

Actuarial modelling is not dissimilar to this scenario, whereby we assess the mean position, and can provide indications of uncertainty within such estimates. Simply because it is difficult to model a particular scenario does not mean that the analysis performed is irrelevant.

Current changes are insignificant compared to past variations

Here the issue relates to the time period that is considered. It is generally accepted that there is no evidence for the global temperature being as warm as its current state during the last 2000 years. Certainly over the ice ages it is expected tha the global temperature was lower, although it is difficult to get accurate readings for sch times in the past. However, the period of 2000 years is not insignificant.

In particular such large changes in temperature, as those relating to the ice ages, are unlikely to be caused by purely changes solar activity, and would need some amplification process by the Earth's environment. Studies of such changes in temperature do not give a simple answer to what causes the strong changes relating to an ice age, with the increase/decrease of plant life and the reflectivity of ice sheets having effects on carbon dioxide emissions and the absorption of heat by the Earth.

The lower atmosphere is cooling

Climate models have predicted that the lower atmosphere will warm at a rate consistent with the surface, although they predict cooling at higher altitudes. A 1992 study showed that this was not the case. However, further investigation indicated that there were errors in the way the data had been adjusted for changes in satellite speed, and also not allowing for improvements to waether balloon design.

A 2006 review allowing for these factors has shown that the temperature in the lower atmosphere is indeed rising, although measurements in the tropics seem to indicate a slower warming than at the surface.

Parts of the world are cooling, not warming

Antarctica has shown a cooling over the last 40 years. In addition a 2006 report indicated that sea temperatures have been reducing slightly.

The sea temperature phenomenon was later retracted by the author as data colection was misinterpreted, leading to spurious results. Similarly other studies have indicated that the sea temperature is not rising as fast as previously thought, although it is still rising.

The Antarctic is predicted to have lower temperatures as precipitation outweighs counteracts over the continent. This tallys with the IPCC report and climate models, which predict a thickening of the ice sheet, counteracting the increased melting of the peripheries. By contrast, the Artic ice sheet has been estimated to have thinned by 40% and decreased in size by 10-15% since the 1950s (with a 66-90% certainty).

Extra-terrestrial influences including cosmic rays are to blame

Solar activity and cosmic rays have also been suggested as causes for climate change. The Sun is definitely a strong influence on the temperature of the Earth. As mentioned above, the ice ages are assumed to have been triggered by varations in solar intensity, although this alone is unlikely to have caused the necessary shift in climate.

However, there is no evidence that solar activity has undergone a trend over the last 40 years, and hence is incompatible with the observed temperature change at the surface. This piece of research seems to settle the debate.

Cosmic rays, being high-energy particles from outside the solar system are scattered by the manetic field of the Sun, and impact the atmosphere. Theories have been made that these particles can cause cloud formation, hence increasing cloud cover and reduce global temperatures. The theory supposes that reductions in the solar magnetic field has reduced the number of these particles hitting the Earth, thus reducing cloud formation and increasing the temperature.

Cloud scientists have yet to prove that such a mechanism for cloud formation exists, or that there is any correlation between cloud formation and cosmic ray intensity.

Finally, there is still significant debate as to whether cloud formation heat or cools the Earth. There are arguments for both, depending on whether they act as a blanket, or a reflective coating.

The temperature readings used to back up climate change are incorrect

The final section I cover reflects a number of claims and counter claims indicated above: that measurement and interpretation of the data is critical, and open to error.

The "hockey stick" graph showing an exponential rise in temperature since 1990 has been the focus of much debate regarding the accuracy and interpretation of the data underlying it. Effects such as urbanisation, "adjustments" to the data and over-fitting of models to the available data have clouded the underlying issues.

The original data has been reanalysed many times, and most of the results lie within the original error bars, with all recalculations showing that the last part of the 20th century has been the warmest over the last 1000 years.

Further reading:

New Scientist

Gristmill: has a detailed discussion of reasons to refute a large number of skeptical comments/arguments

Realclimate (2 links):

http://www.realclimate.org/index.php/archives/2004/12/index/#Responses

http://www.realclimate.org/wp-rss2.php

Sourcewatch

Met office

Cosmic Rays: "The Chilling Stars", Calder and Svensmark.