Three letters doubting global warming appeared in The Canberra Times print edition on Tuesday 23 June 2009.

A letter from Tom Waring mainly asks about uncertainties:

Crispin Hull (“Problem’s not in the climate science, it’s all in the mind”, Forum, June 20, p15) scoffed at Senator Fielding accepting religious myth while rejecting climate science.

But Hull could have gone the other way. He could have observed that religious irrationality demonstrates humanity’s propensity for mass hysteria.

He could have noted science is often part of sustained errors of conventional wisdom, and allowed the possibility that the scientific underpinnings for imminent climate Armageddon could be more human hubris. For example, does science really know what caused the many hundreds of climate oscillations of the known past?

Was their atmospheric CO2 cause or effect? What stopped them? Were they all really just (poorly-understood) cycles in the earth’s orbit?

When is the next cyclical ice-age due? Do we fully understand cloud formation? Won’t whatever caused (and ended) them happen again? Now?

Some agnosticism seems respectable.

Tom Waring, Ainslie

Aert Driessen wrote about CO2 lagging temperature:

Tony Kevin (Letter, June 18) uses a lot of words to show a correlation between fluctuating CO2 and fluctuating temperature from ice core data over the last 800,000 years, which is true, but what he has omitted to add is that close examination of that correlation shows that temperature changes happen before CO2 changes, by up to 800 years.  That is to say, CO2 fluctuations are the result (and not the cause) of temperature variations.

For those of us that learnt in school that CO2 is more soluble in cold water than in warm water (not really intuitive) that relationship between the variables makes sense when you consider that beer goes flat when it gets warm.

Aert Driessen, McKellar

And a brief piece from Owen Reid:

Instead of ridiculing the man (Steve Fielding), and his Christian faith, perhaps Crispin Hull (“Problem’s not in the climate science, it’s all in the mind”, Forum, June 20, p15) should be asking why the questions put to Minister for Climate Change Penny Wong, have not been answered.

Owen Reid, Dunlop

I responded to Aert Driessen with a letter to the editor, published on Friday 26 June:

Aert Driessen (Letters, 23 June) correctly points out that, in most of the global warming events during the last 650,000 years,  CO2 began to increase around 800 years after temperature started to rise.  However, he then concludes that CO2 fluctuations are the result, not the cause, of temperature changes.

This is a common misunderstanding. The reality is that CO2 is not simply the cause or the result of warming – it is both. CO2 and temperature are influenced by many factors.   Warming events over the last 650,000 years have followed a clear pattern.  Changes in the Earth’s orbit around the Sun (known as Milankovitch cycles) slowly warm the planet.  This warming triggers increases in CO2  and other greenhouse gases in the atmosphere, which cause further warming, and so on in a positive feedback cycle until a new equilibrium at a higher  temperature and CO2 level is reached.  These positive feedbacks – due to ice loss reducing albedo, the melting of permafrost, and other processes – are potential “tipping points” that are among the most worrying aspects of the current warming.

So CO2 has acted as an amplifier of other climatic influences.  In recent times, we’ve accelerated and short-circuited that process by pumping extra CO2 directly into the atmosphere.  As a result, we’re seeing  temperatures rising five times faster, and CO2 increasing around fifty times faster, than during past natural warming events at the end of ice ages.

This – the unprecedented speed of the change – is one of the core dangers of the current global warming to human society.  The ecosystems on which we rely have never had to deal with anything like the rate of change in climate that we’re now causing.  It is increasingly looking as if the “safe” level of CO2 is no more than 350 parts per million.  We are already at 380 ppm – a higher CO2 level than humans have ever experienced.  That’s why the currently proposed Carbon Pollution Reduction Scheme, with its target of a mere 5% reduction in emissions by 2020, is utterly inadequate.   We now need to move rapidly beyond 100% reduction into an economy which produces a net lowering of CO2 and other greenhouse gases.