I refer to this letter Global warming theory nothing but hot air .

The writer of the letter espouses the position that we should always try to verify what we hear and say, and to base our conclusions on facts. I wholeheartedly agree with this. However, his letter itself not only falls short of this standard, but, in fact, falls far short.

The writer pretends to apply rigour to his arguments about the falsehood of global warning, but in reality it is just that - pretense. Climate change is an important issue facing us today and we owe it to our children, if not ourselves, to act on this based not on superficial ‘research' as evidenced by the letter, but a deeper understanding.

In summary, the following points were presented by the letter in question:

1. CO2 exists only in tiny amounts in the atmosphere (0.03%), hence it is ridiculous to think that it is a major contributor to global warming.

2. Global historical temperature cannot be accurate, given the fact that measuring equipment changed so much since 1900. This affects the final results and conclusions.

3. There is no scientific consensus about global warming. In fact, the author alleges that there are countless credible scientists in top universities disputing the causes of global warming, which actually contradicts his statement earlier that if you Google ‘hard enough' you can find dissent.

It is surely very easy to Google opinions of countless top scientists.

4. The IPCC is not a credible organisation; it is comparable to a ‘washing machine salesman'. The writer also claims that the IPCC is also the only organisation that pushed the agenda of global warning (‘they are only quoting the United Nations Intergovernmental Panel on Climate Change')

5. The writer alleges that humans cannot be ‘so great' as to cause something on the scale of global warming.

The arguments above pave the path for the writer to claim that global warming is a trillion dollar scientific hoax. However each of the above points are false. Details on that below.

1. Carbon dioxide does indeed form a very tiny fraction of our atmosphere. However, what is relevant is not the amount, it is the effect. The argument presented by the writer is akin to saying two miligrams of cyanide certainly is not toxic, since it is such a small amount.

Scientists have in fact estimated the relative contribution of the different greenhouse gases, and although water vapour is the most important component, C02 is in fact a very significant contributor (somewhat less than half the effect of water).

See Table 3 on Page 203 of this paper .

2. This point is again patently false. The writer is trying to appeal to ‘common sense' of the reader, in that we all know that gadgets and technology improve and change at a rapid pace, and hence it is foolish to rely on temperature readings from decades ago.

However, the physics of thermodynamics is well understood since the days of Lord Kelvin and Carnot. More than that, studies have been made to study the potential inaccuracies of the temperature records, and the conclusion is:

‘Since the mid-20th century the uncertainties in global and hemispheric mean temperatures are small and the temperature increase greatly exceeds its uncertainty. In earlier periods the uncertainties are larger, but the temperature increase over the 20th century is still significantly larger than its uncertainty.'

3. Lack of scientific consensus supporting global warming. The writer claimed this without citing even one of his ‘countless top scientists' that actually dissented. One study encompassing close to one thousand articles on climate in peer-reviewed scientific journals showed that 75% gave explicit or implicit agreement to the consensus view on global warming, with the remaining 25% taking no position. More to the point, none dissented .

The scientific consensus is clear and unmistakable on global warming, with many, many official statements made by scientific organisations and individual scientists. One example is this statement by the national academies of science of all the major industrial nations.

4.The IPCC has had criticisms levelled against it, certainly. One thing the writer neglected to mention is that while there are criticisms that the IPCC is over-emphasising the risks of global warming, equally there are criticisms that say the IPCC is being too understated about global warming.

Note also that the IPCC has received many accolades as well, perhaps none higher than the 2007 Nobel Peace Prize (one of the very few awarded to organisations rather than individuals)! Surely a tall order for a mere ‘washing machine salesman'?

5. On the vast scale of our universe, or even on the scale of the pale blue dot that is our planet Earth, humankind is indeed very small. However, we underestimate our own destructive power at our peril.

Doubly so since we have long since demonstrated our capability for destruction - for example nuclear weapons and mutual assured destruction, or the depletion of the ozone layer (the downward path of which was arrested by collective action much like what is being attempted for global warming now).

There are indeed forces bent on denying the scientific evidence related to climate change, but in the opposite direction as that stated by the writer. The most p owerful force of all may be the businesses whose profits depends on humankind continuing unabated on this downward path, and the politicians funded by these businesses.

The frame of our public discussions on climate change must be informed by an accurate picture of scientific research. I hope the clarifications above will contribute, and I hope that the standard of our discourse on this and other scientific issues will be maintained at a reasonable standard.

Our actions, or lack thereof, in this generation will have a profound effect on the future of the planet and of all humankind. This profound importance must dictate our level of care in seeking an understanding of the issues.