Paul Pollard (Letters, August 12) claims the climate change debate is not helped by trotting out the same old, often-refuted denialist debating points.
The reason these debating points are continually trotted out is because there is still no scientific evidence that adding more CO2 to the atmosphere forces temperatures up further and until that evidence is provided, the questions will continue to be debated.
Consider that greenhouse gases represent 2percent of the Earth's atmosphere. Carbon dioxide represents 3.6percent of those greenhouse gases (there are 87 of them).
We dastardly humans contribute 3.4percent of that CO2 to the atmosphere. Us nasty Aussies (living in the third least densely populated country in the world) contribute 1.4percent of the total emissions in the atmosphere.
And our Government claims we can save the Barrier Reef, Kakadu, the Murray Darling Basin by taxing each and every one of us thousands of dollars in a vain attempt to reduce that already ridiculously low emissions figure that will not make the slightest difference to our climate. The CO2 rises in the atmosphere since 1750 are hardly ''unprecedented'' and there is no evidence the latest decade has been the hottest in thousands of years.
If CO2 was the major driver, temperature would rise indefinitely in a runaway greenhouse effect but this hasn't happened in 500 million years.
There is a mountain of evidence on the effects of climate change but we are yet to be provided with any evidence showing higher CO2 means significantly higher temperatures.
In fact the Earth slipped into an ice age when CO2 levels were higher than today.
Whatever warming effect carbon dioxide has, it has been historically proven to be no match for other climatic forces out there.
Anthony Moore, Calwell
Paul Pollard (Letters, August 12) writes approvingly of climate models.
The Intergovernmental Panel on Climate Change also bases its prediction on the consensus of climate models. What is not often realised is that all of these models include tunable parameters.
These are critical variables where there is no experimental or empirical evidence as to what values should be selected.
So they can be and are used to produce the results that are desired.
It is also known that the different modellers have exchanged code for their models, which weakens their claims to independence.
Finally, the models do only a so-so job at predicting the broad distribution of present-day temperature.
When it comes to the critical issue of rainfall, according to the ANU data recently published, their simulations of average present-day Australian rainfall, which as a measured value is about 450mm per year, ranges from less than 200mm per year to 1000mm per year.
Nor are climate models able to simulate the major fluctuations well attested to in the past 2500 years, including the Roman warming, the Dark Ages cooling, the early Medieval warming and the Little Ice age of about 1400 to 1820, none of which can be attributed to human-sourced CO2
Pollard states, ''They [that is, the models] can thus broadly explain global temperature increases, and validate greenhouse science understanding about the climate.''
He fails to realise that models in principle can ''explain'' nothing; they are simulations.
In the circumstances, I suggest they are not worth the proverbial bucket of warm spit.
Dr John Penhallurick, Fraser
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