Archive for category science and nature

Crikey’s resident climate denialist

Crikey, a prominent daily news email to which I subscribe, has a few climate denialists who pop their heads up from time to time in the Comments section. The most vocal is Tamas Calderwood, who produced this piece yesterday (in response to an article by Clive Hamilton about civil disobedience in the face of government inaction on climate):

Tamas Calderwood writes: Clive Hamilton’s call for civil disobedience is a disgrace. His own lazy arguments and lack of supporting data can’t persuade people that “the fate of the planet hangs in the balance” so he now dismisses democracy and demands action. Meanwhile, the global temperature in August 2009 was 0.23C above the 30-year mean so there’s still no sign of the coming apocalypse. Given that the temperature data supports the climate sceptics, would it be moral for us to take ‘direct action’ against the likes of Hamilton and Greenpeace? Would civil disobedience to stop the absurd and utterly ineffectual ETS be justified? I am as certain of my scepticism on this issue as Hamilton is of his doom mongering pessimism but we sort this stuff out at the ballot box in this country. I would have thought a “Professor of Public Ethics” would know that.

I responded with this in the 15 September edition:

Matt Andrews writes: Tamas Calderwood maintains his fine tradition of breathtakingly ignorant letters on climate change with a couple of claims (Letters, 14 September) just ripe for the puncturing. The first is “the global temperature in August 2009 was 0.23C above the 30-year mean”. Presumably Tamas is trying to paint a picture of negligible warming that doesn’t warrant strong action, but in fact this data point is embarrassingly devoid of meaning.

Let’s take a step back: “climate” is roughly defined as “the average of the weather over the long term”, where “long term” is usually defined as at least 30 years. Short term temperatures – the single month that Tamas cites, or even annual averages – are dominated by the wild ups and downs of the weather, the “noise” in the long term signal. The warming trend caused by human releases of greenhouse gases is very clear over the last thirty years or hundred years, but if you restrict your time period tightly enough, it’s swamped by the natural chaos of the weather.

Tamas neglects to mention that the data he’s quoting is the denialists’ favourite: UAH satellite figures. Satellites don’t measure surface temperature; they measure temperature across large cross-sections of the stratosphere and upper troposphere. That is then processed to generate an estimate of lower troposphere temperature. This is not the same as direct surface temperature measurements, for which there are several global average indexes of high statistical quality, the best of which are Hadley HadCRU and NASA GISS. Substantial issues have been raised in recent years over implausible anomalies in UAH data.

Tamas says “there’s still no sign of the coming apocalypse”; that in itself is very much debatable, but on the face of it he wants us to wait until we have a global disaster on our hands before acting – a suggestion so spectacularly foolish that I need say nothing more on it.

More seriously, Tamas has clearly failed to understand that the climate issue is one of minimising risk. There are substantial uncertainties over what might happen in the coming decades, and, yes, some of them are near-apocalyptic, at least for contemporary human civilisation. That might be a low risk, but it is not insignificant, and it includes several quite plausible scenarios which could play out at very short notice. More broadly, there are major impacts which are already at a high risk of occurring over the next few decades.

Tamas goes on to announce that “the temperature data supports the climate sceptics”. This is in fact (unintentionally) correct – the genuine “climate sceptics” are the mainstream climate scientists. Scepticism lies at the core of science: new data is critically examined both in terms of its soundness and against the context of the established evidence. Conversely, those who label themselves “climate sceptics” are usually the opposite: credulous and ill-informed, sucking up whatever factoid they come across on denialist blogs, and resolutely refusing to educate themselves about the big picture. What he’s trying to say is that the temperature data refutes mainstream climate science – a claim which is manifestly and comprehensively false.

If Tamas is able to provide some kind of substantial evidence to back this assertion, I’m sure that climate scientists the world over would be very interested indeed.

Update: Tamas Calderwood then responded in the 16 September edition with this:

Tamas Calderwood writes: Matt Andrews (yesterday, comments) asserts the satellite temperature record is irrelevant because it doesn’t include surface readings or look directly at the troposphere.

First, the surface station record is unreliable because of the urban heat-island effect and appalling maintenance and placement of measuring stations as found by Anthony Watts, but even the data sets that include surface stations show no warming for a decade.

Second, satellites do measure the troposphere and I specifically used the troposphere data from UAH. The troposphere accounts for 75% of the atmosphere’s mass and 99% of its water vapour.

Matt then goes on to discuss “high risk” “plausible scenarios” that ” might happen” — in other words, he can point to no actual serious global warming but despite “substantial uncertainties” he asserts this will be “near apocalyptic … for contemporary civilization”.

Kieran Diment (yesterday, comments) says I ignore 80% of the data but makes no mention of what this 80% is.

Mark Byrne (yesterday, comments) asks if I “will only be convinced of dangerous global warming after it has occurred”? Well, yes Mark, because despite record human CO2 production no dangerous global warming has actually occurred and the Medieval and Roman warm periods were warmer than today anyway.

In the mean time I’ll again point out that the past 30 years has seen a trend increase in Earth’s atmospheric temperature of 0.38C, the past 10 years has seen about 0.1C of cooling and the Argos buoy program shows ocean cooling since 2003. Average temperatures for the past 15 years have been less than 0.2C higher than they reached in the 1940’s and the past 12 months has been around 0.4C warmer than the average since 1901.

This is not a crisis and I don’t think we need to abandon democracy and enslave ourselves to those who know the TRUTH of global warming when the data don’t support their claims of Armageddon.

Update: I responded with this in the 17 September edition:

Matt Andrews writes:
Tamas Calderwood (Letters, 16 September) demonstrates stereotypical behaviour from those who label themselves as “climate sceptics”: be uncritically accepting of any argument found on denialist blogs, assume these arguments are better grounded than real peer-reviewed research, and refuse point blank to learn about the big picture of climate science.

His latest letter (in between misquoting me five times) breathlessly repeats a string of endlessly recycled and long-debunked talking points direct from the “Watts Up With That” climate denial blog, infamous among climate scientists for the shallowness and ignorance of its commentary.

For example: “the surface station record is unreliable because of the urban heat-island effect and appalling maintenance and placement of measuring stations as found by Anthony Watts”… in reality, these issues have been long understood and adjusted for, and the real issue – temperature trends – is very strongly correlated across a huge range of surface data sources. For example, the warming trend is just as strong on windy nights as on still nights; if the urban heat island effect were significant, there would be slower warming observed when looking only at windy nights. Big picture: urban heat island and siting issues have a trivial effect on large-scale temperate trend data.

Or “the Medieval and Roman warm periods were warmer than today anyway”: false, false, false, false, false.

And so on and so on. What’s amazing to me is that people can be interested enough in this stuff to devote many hours to digesting wingnut blogs… and yet utterly fail to spend some time learning the basics about contemporary climate science.

Update: Tamas has responded in the comments, so the conversation is continuing here.

Earth: The Climate Wars

Just finished watching a nicely produced TV series called Earth: The Climate Wars. It was originally screened in 2008 on BBC2 in the UK, and as far as I know hasn’t yet been broadcast here in Australia. You can see it in three one-hour segments at or in eighteen ten-minute segments at YouTube.

Presented by Dr Iain Stewart, a Scottish geologist at the University of Plymouth, it gives a general audience a nice taste of the world of climate science. Stewart presents well: he’s engaging and personable. His comments on making the series, and the way his views on climate change have changed, are worth reading too.

The first episode mainly looks at the history of climate science up to around 1990. The second covers the “fight back” of arguments against anthropogenic climate change. It looks at what the main criticisms were, and how they were examined and debunked, mainly over the course of the 1990s. The third hour looks at the future: climate models, projections, and uncertainty.

Even though much of the material was familiar, it’s great to see the story retold in a visual, highly polished format. It’s good viewing – well worthwhile.

Of debates and doubt

In the print edition of The Canberra Times of Saturday 15 August 2009, this letter appeared:

Danielle Cronin in her article “Flawed logic used to oppose green Bill” (August 13, p5) stated that Will Steffen declined an invitation to make a presentation along with Professor Bob Carter before the Senate.

That is not surprising, as Al Gore wouldn’t appear and debate with climate sceptic Lord Monckton before the US Senate either.

Do you see a pattern developing here?

Is Steffen afraid that he won’t be able to hold up his end in a debate?

You can bet on that.

The alarmists have only computer climate models (fantasy computing) to use as evidence and that is no evidence at all.

Is there evidence of a vested interest in supporting this foolish theory?

John McKerral
Batemans Bay, NSW

My response:

John McKerral (Letters, August 15) tries to condemn modern climate science in general because Will Steffen, an eminent climate scientist with the ANU, declined to debate the discredited Bob Carter face to face in front of the Senate. I can’t speak for Steffen, but I can understand why he wouldn’t. It’s similar to the situation with creationists: they are utterly lacking in genuine scientific evidence for their position, but they can score points through the strange compressions and distortions of face to face debate, where verbal agility, cute anecdotes and one-liners win the day. Science doesn’t work that way: conclusions are carefully built up from a large body of thoroughly documented and widely-reviewed evidence. Debating whether the world is warming, and whether humans are mainly responsible, makes about as much sense as spending Senate time on a debate over whether smoking causes cancer.

McKerral also asserts that climate science has nothing more than computer models as evidence. This is not just incorrect; it’s the diametric opposite of reality. The observational evidence supporting the conclusion that the world is warming, and that human activities are the primary cause, has moved beyond being a mountain; it is now better described as a mountain range. On the other hand, the evidence of any substance against it is, to a first approximation, non-existent. That’s the scientific picture, and it bears little resemblance to what passes for analysis in many a dingy corner of media commentary and politics.

Matt Andrews, Aranda

CO2 muddleheadedness

A long thread of letters in The Canberra Times print edition, centring on curious claims by Tim Curtin.
First this letter appeared on Friday 31 July 2009:

The article “No time to lose as climate change turns to the worse” by Will Steffen, director of ANU’s Climate Change Institute (July 27, p9) contains some questionable statements as “fact”.

Steffen asserts “the climate system is now moving faster than we had thought likely a decade ago… the rate of accumulation of carbon dioxide in the atmosphere has increased since 2000 because of the growth in the global economy and the relative weakening of the natural processes that absorb carbon dioxide from the atmosphere”.

These statements are incorrect. The rate of growth of annual net increases in the atmospheric concentration of carbon dioxide was 7.44 per cent a year from 1960 to 1969, 10.01 per cent from 1970 to 1979, 7.16 per cent from 1980 to 1989, 4.55 per cent from 1990 to 1999, and just 2.8 per cent from 2000-2009 (the rates are for the years ending in June). Thus growth of net increases in atmospheric CO2 has been much slower than at any other time since records began at Mauna Loa in Hawaii in 1958.

It follows that while Steffen is right about rapid growth of the world economy from 2000 until 2008, he is wrong to say that “relative weakening of the natural processes…” explains his assertion that “climate change is turning for the worse”. The evidence is for strengthening those natural processes, namely the annual increase in photosynthesis that has accounted for more than half of all anthropogenic emissions of CO2 since 1959 – and explains the decline in the growth of those net emissions to Steffen’s “atmospheric accumulation”.

Tim Curtin, associate, RMAP, ANU

This was followed by assorted replies (including one from RMAP saying that Curtin was not in fact an associate of RMAP at all!).

Curtin then responded on 7 August with this:

Nick Ware (Letter, August 4) challenges my demonstration (Letters, July 31) that growth rates in atmospheric concentration of carbon dioxide have declined from 1960 to 2009.

He suggests I was using the “third derivative” – I wish I knew what that is! I simply derived the semi-logarithmic growth rates for each decade, those being the first derivative, like a normal compound interest growth rate over the period in question. The second derivatives (ie, the rate of change of the rate of change) also decline if you can be bothered to calculate them (unlike Will Steffen).

More seriously, Steffen in his article in The Canberra Times (“No time to lose as climate change turns to the worse”, July 27, p9) and in his piece (co-signed by 15 other worthies) in The Sydney Morning Herald (August 1) relies on James Hansen’s temperature data (NASA-GISS) which relies almost exclusively on temperatures measured at airports with ever-increasing planes, people and parked cars.

The truth is that at Mauna Loa where the atmospheric carbon dioxide level is measured, there is virtually no discernable trend in temperature since 1958, and none at all since 1978.

Finally, I must confess that when I signed my letter of 31 July I thought I was still an associate (unpaid) of RMAP at ANU. Sadly that is not the case, but even if I had been, I should not have used that designation.

Tim Curtin, Spence

My response:

Tim Curtin (Letters, 31 July and 7 August) makes a series of basic errors in his statements on climate change. The first is that it would make sense to measure the growth in carbon dioxide as if it were like compound interest. It doesn’t. Back to basics: CO2 increased by an average of 0.85 parts per million each year during 1960-69, by 1.27ppm for 1970-79, 1.60ppm for 1980-89, 1.50ppm for 1990-99, and by an average of 1.87ppm a year for this decade. There’s a clear long term trend here: the CO2 level is going up, and over time the amount it’s increasing by each year is growing. We’re already at around 390 parts per million: a higher level than humans have ever experienced, and already higher than the 350ppm that is increasingly regarded as the probable safe level for ecological and climatic stability.

Another error is the implication that the entire body of land surface temperature data – as used by NASA-GISS, Hadley, and many other climate science centres – is suspect, with the assertion that they rely “almost exclusively on temperatures measured at airports with ever-increasing planes, people and parked cars.” This is broadly known as the “urban heat island effect”, but it is well understood in meteorology and climate science, and temperature data is correlated and carefully adjusted to account for it. A series of studies published in Nature in 2004 compared temperature readings taken on calm nights with those taken on windy nights. The urban heat effect should be much stronger on calm nights, but the temperature trend was very strongly correlated. Overall the adjusted temperature data is sound, and is not undermined in any significant way by urban heat effects. The evidence for the warming trend is so strong that it’s essentially incontrovertible at present.

It’s amazing to me how armchair experts who clearly are not familiar with the science so often have the hubris to believe that they have some extraordinary insight that instantly overturns the entire scientific consensus. In reality, natural sciences don’t work that way. It’s all about the building up of many layers of evidence from a wide range of research teams, data sources, and physical systems, and arriving at conclusions based on the balance of probabilities. To date, there is no substantial evidence that constitutes a serious challenge to the mainstream science. The level of noise in the media from those who refuse to concede that humans are in the process of causing severe climate disruption is utterly out of proportion to their scientific strength of their arguments.

Matt Andrews, Aranda

Warming, accelerated

A letter appeared in The Canberra Times print edition of Saturday 1 August 2009:

Mark Diesendorf begins his article, “It’s power to the people on climate change action” (July 29, p11) with the cliche that all alarmists love, “Global climate change is accelerating”. I assume he means warming. That is simply not true. But as a scientist I cannot accuse him of lying because nothing in science is ever “settled”. But I am entitled to ask him on what evidence he bases his claim, and on behalf of CT readers I do so herewith.

Aert Driessen, McKellar

It refers to an earlier article by Mark Diesendorf (which is not online, due to The Canberra Times‘ ludicrously poor approach to online material: most opinion pieces and a lot of the print content is never made available online).

My response, published on 4 August:

Aert Driessen (Letters, August 1) asks for evidence that global warming is accelerating. Firstly, what does the word “climate” mean? It means the long-term average of the weather, generally defined to be over periods of 30 years or more. Temperatures have a lot of short term variability: they bounce up and down from year to year. The important aspect is the long term trend.

Taking the most commonly cited data for global temperature, from the Hadley Meteorological Centre in the UK, the picture is clear. Annual averages, dominated by short term variability (the “weather”), bounce up and down all the time, but 30-year averages, showing the underlying trend (the “climate”), have been rising since early in the 20th century, and especially since about 1975.

Specifically, the 30-year average shows a warming rate of 0.88 degrees per century in 1989, a rate of 1.10 degrees per century in 1999, and a warming rate of 1.52 degrees per century in 2009. Looks like acceleration to me.

Matt Andrews, Aranda

A note on the details of the above figures: I drew the annual global average temperature data from HadCRUT3 (combined land and marine surface temperatures), then calculated the 30-year averages (what I describe as the “climate” as opposed to the “weather” annual averages). The warming rates I cited are the average for the preceding 10 years in each case. So “0.88 degrees per century in 1989” means that the average annual rate of increase in “climate” temperatures over the ten years to 1989 was at a rate of 0.88 degrees per century. I should probably have made it clearer by rephrasing it like this:

The 30-year average shows a warming rate of 0.88 degrees per century during the 1980s, a rate of 1.10 degrees per century in the 90s, and during this decade we’ve seen a warming rate of 1.52 degrees per century.

The graph, the Senator, and the weather-watchers

Australian Senator Steve Fielding has attracted quite a bit of media attention with his series of stunts aimed at building doubt over the scientific basis for anthropogenic global warming.  The core of his campaign has been a carefully constructed graph which shows no clear rise in temperatures while CO2 continues to rise since 1995.  The implication is that the world is not warming and CO2 is not (directly) related to temperature.

Trouble is, he (apparently) thinks he’s looking at climate – but he’s not.  He’s looking at the weather.

Climate is defined as the long-term average weather, where “long term” is generally accepted to mean at least 30 years.   Anything on a shorter time scale is dominated by short term variability: weather.

The graph Fielding cites shows year-by-year data: annual average global surface temperatures.  So each data point is the average of a one-year period.  That’s a nice picture of the weather; but why don’t we take a look at the climate?

Here’s a graph from the same data set (Hadley CRUT3) showing the annual average temperature (the brown spiky line, jumping up and down all the time) and the 30-year average temperature (the smooth yellow line).

Annual temperature vs. 30-year average temperature

Brown = weather.  Yellow = climate.


unwarranted authority

A surprising letter in The Canberra Times print edition of Saturday 4 July:

I thank Matt Andrews, of Aranda, for sharing with the people of Canberra his great wealth of knowledge concerning climate change.

It is clear to readers of his authoritative letters that he is a detached academic with many letters after his name, unlike those who simply regurgitate read material or merely express an opinion.

Along with Crispin Hull I feel for him on his nightly agonising about those exploiting scientific illiterates who disapprove of current climate science.

Bob Edwards, Kambah

Well, my thanks go out to Bob Edwards for this unexpected praise.

However, I should point out that I’m neither an academic nor do I have any letters after my name… I’m just an interested bystander.  I’d dearly like to devote my time to the study and practice of climate science, but for now I’m merely a humble web developer with an occasional bee in the bonnet.

An amusing follow-up letter arrived in the Tuesday 7 July print edition:

Bob Edwards (Letters, July 4) condemns himself and proves a point that climate scientists (the sceptical ones) keep trying to make.  When he pours adulation on to Matt Andrews (and Crispin Hull) for their alarmist views on climate change and then uses derogatory language to belittle and ridicule those with another view, he is not contributing to the debate but defending religious dogma.

Aert Driessen, McKellar

Fairly standard denier tactics: try to frame the mainstream science as “alarmist” (or “religion”) and to give the impression that there are two substantial sides to the scientific debate.  Sadly this perception is a long, long way from where the science actually is.

Given the strength of the evidence for anthropogenic global warming in general, this is now essentially the same as a tobacco lobbyist describing the suggestion that cigarettes cause cancer as “alarmist”, or an anti-vaccination crusader damning the conclusion that vaccination can be effective against disease as “religious dogma”.

In search of instrumental errors

A letter from John McKerral in The Canberra Times print edition of Thursday 25 June 2009:

Crispin Hull (“Problem’s not in the climate science, it’s all in the mind”, Forum, June 20, p15) has fallen into the typical alarmist’s behaviour: attacking the character of any organisation or person who has a different opinion on the subject to his own.

Science does not operate that way.

The theories and observations supporting them are what counts, not the character of the person putting them forward.

But it is so easy to attack someone’s character.

As he is so fond of science, he should consider that the alarmist scientists have destroyed their own theory.

They and their models predict that if the warming that we have experienced is caused by greenhouse gases (GHG), there should be a hot spot about eight to 12 kilometres above the tropics.

That is to say the warming there should have been at a rate 1.5 to 3 times the rate of warming at the surface in that area.

50 years of weather balloon and thirty years of satellite data has not shown this to be so.

In fact it is the other way around, the near surface temperature increase has been between 1.2 and 1.4 times that of the supposed hot spot.

Also the Earth Radiation Budget Experiment Satellite has shown that the outgoing long wave radiation has diminished by only 1/7 of that predicted by the computer climate models and this fails to support the GHG theory.

That radiation is supposed be absorbed by the GHGs on its way to space thus diminishing the outward radiation.

It is not and that is another nail in the coffin of that theory.

Under normal circumstances that should have finished the GHG causes global warming/climate change theory. However this is zombie science, you can’t kill it.

Governments keep pouring money into it thereby keeping it going.  The climate has always changed without man’s help and will continue to do so.  So-called deniers do not disbelieve that the climate is changing.

What they do deny is that man has a major influence in the process.

It might be to Crispin’s benefit to do some research on the subject!

John McKerral, Batemans Bay, NSW

I sent this response to The Canberra Times, published in the 2 July print edition:

According to John McKerral (Letters, 25 June), the entire body of scientific evidence for human-caused global warming is invalid, and “alarmist scientists have destroyed their own theory”.  This bold claim is apparently proven by two rather lightweight quibbles over climate models.

The first, that the upper troposphere has warmed more slowly than the surface, was a favourite for several years among those trying to deny the scientific consensus, until it was shown in 2005 that the data involved included instrumental errors – such as sunlight warming instruments carried on balloons – that had not been properly accounted for.  While there are still some small discrepancies between climate model projections and warming over the tropics, they fall within the expected range of error and do not even remotely constitute a flaw in the mainstream science.

The second complaint, that the drop in outgoing long-wave radiation was not as much as predicted, was raised in late March by Richard Lindzen, a prominent denier (and recipient of funding from oil companies).  Unfortunately Lindzen neglected to mention that the graphs he was citing were out of date, containing data with significant instrumental errors (including the slow loss of altitude of the satellite’s orbit) which had not been properly corrected.  The updated graphs do not support his argument at all.

It’s disturbing that our society’s general level of scientific literacy is so low that these kinds of issues can be interpreted as constituting a disproof of current climate science. The big picture is that the evidence from a wide range of sources overwhelmingly supports the conclusion that human activities are the primary cause of  current global warming.    Our lack of scientific literacy is exploited by those who are actively seeking to delay or reduce action on global warming.  History will not judge them kindly.

Matt Andrews, Aranda

The bridge on the Titanic

A comment I made on a post by Ove Hoegh-Guldberg about a piece by Paul Krugman re the denialists in the US Congress trying to vote down the Waxman-Markey bill:

It’s very interesting to see how we are facing increasing tension, in some ways, between the desire for open discussion and tolerance of a diversity of views on the one hand, and the extreme urgency for effective action on the other.

The various darker forces in this field – the professional purveyors of disinformation, such as those that have guided Senator Fielding in his recent stunt – have managed to effectively create an impression in the minds of many that there is genuine scientific debate and doubt over the fundamental aspects of AGW: that the world is warming, that human activities are responsible. An impression that is entirely false, and in many cases an impression that is created with downright fraudulent claims. “Doubt is our product”, as they say.

We literally have the infamous tobacco lawyers, and those that have learned from them, being given a voice in the media to an extent that the tobacco lobby itself has not had for decades; and yet the evidence for anthropogenic global warming is, if anything, even more overwhelmingly strong than the evidence against tobacco.

It’s a measure of our deep scientific illiteracy as a society that AGW deniers are given this extraordinary level of airtime, print space, and influence. If journalists, politicians and commentators had learned enough about the natural sciences to get a perspective on the relative weight of evidence, the situation would be very different.

How close does the Titanic have to get to the iceberg before those who loudly claim there’s no need for action are ordered off the bridge?

CO2 lagging temperature

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.