Science Blog

Response to new book: 'Nine Facts about Climate Change'
Associate Professor Kevin Walsh - University of Melbourne
1 March 2007

Kevin Walsh is an Associate Professor in the field of Climate Change at the University of Melbourne's School of Earth Sciences. Below, Kevin responds to seven of the nine main points raised in the book: “Nine Facts About Climate Change” by Ray Evans.

1. 'Climate change is a constant. The Vostok Ice Cores show five brief interglacial periods from 415,000 years ago to the present. The Greenland Ice Cores reveal a Minoan Warm Period 1450–1300 BC, a Roman Warm Period 250–0 BC, the Mediaeval Warm Period 800–1100AD, the Little Ice Age and the late 20th Century Warm Period 1900–2010 AD.'
 
Agreed. The real question is not whether climate change occurs, but what is causing it. In his supporting argument to this statement, Mr. Evans believes that there is a natural “upper bound” to Earth’s temperature over the past million years. This may be true but is hardly relevant when we are faced with increases in greenhouse gases in the 21st century to levels that are well beyond anything experienced in the past several hundred thousand years.
 
2. 'Carbon dioxide is necessary for all life on earth and increasing atmospheric concentrations are beneficial to plant growth, particularly in arid conditions. Because the radiation properties of carbon dioxide in the atmosphere are already saturated, increasing atmospheric concentrations beyond current levels will have no discernible effect on global temperatures.'
 
There is no scientific justification for the second statement whatsoever. Carbon dioxide concentrations during the Cretaceous period were several times what they are now, and global temperatures were higher also. Venus has a very thick carbon dioxide atmosphere, and so surface temperatures are hot enough to melt lead. Also, his supporting argument to this statement totally ignores the significant contribution of climate feedbacks towards amplifying the radiation effect of carbon dioxide concentration increases.
 
3. 'The twentieth century was almost as warm as the centuries of the Mediaeval Warm Period, an era of great achievement in European civilisation. The recent warm period, 1976–2000, appears to have come to an end and astro-physicists who study sunspot behaviour predict that the next 25–50 years could be a cool period similar to the Dalton Minimum of the 1790s-1820s.'

Maybe – but only if the increase in CO2 over the next 20-50 years has no impact, and in any event his supporting arguments provide no estimates of the size of the projected solar cycle change impacts on surface temperatures. In contrast, the IPCC actually did estimate what the size of the solar radiation changes were in the 20th century and what there effects on surface temperatures might have been, and concluded that they were only a small portion of the observed twentieth century warming.
 
4. 'The evidence linking anthropogenic (man-made) carbon dioxide emissions and current warming is limited to a correlation which holds only for the period 1976 to 2000. Attempts to construct an holistic theory in which atmospheric carbon dioxide controls the radiation balance of the earth, and thus determines average global temperatures, have failed.'

Again, this is basically the argument put forward in question 3. Evans shows a graph which indicates that temperature change and fossil fuel use over the period since 1860 are both trending upwards, but because the temperature curve varies more than the fossil fuel curve, he claims that therefore they are unrelated! The climate system is variable; we know that and scientists have good arguments to account for much of this variability: there is some internal variability like El Nino, some solar variations, and some effects by man-made soot and dust particles.
 
5. 'The anthropogenists claim that the overwhelming majority of scientists are agreed on the anthropogenic carbon dioxide theory of climate control; that the science is settled and the debate is over; and that scientific sceptics are in the pay of the fossil fuel industries and their arguments are thus fatally compromised. These claims are an expression of hope, not of reality.'
 
This is a value judgement that I will not comment on, except to say that the arguments in favour of global warming being caused by CO2 are pretty compelling, and nothing in Evans’s document has changed my mind on that. Still, we ought to be wary of stifling scientific debate on this issue – I mean, climate scientists certainly do not know everything there is to know about the climate of the Earth.
 
6. 'Anthropogenists such as former US Vice President Al Gore blame anthropogenic emissions of CO2 for high temperatures, droughts, melting polar ice caps, rising sea levels and retreating glaciers, and a decline in the polar bear population. They also blame anthropogenic CO2 for blizzards, unseasonable snow, freezing weather generally and for hurricanes, cyclones and other extreme weather events. There is no evidence at all to justify these assertions.'
 
He has a point here. It’s not scientific to blame every blizzard or drought on global warming, and there have been unsubstantiated claims regarding this.  But sea level rise is a really poor choice in this list, because every method that has realistically measured global sea level has concluded that it is rising. In his supporting argument for this statement, Evans claims that the main cause given for sea level rise by the “anthropogenists” is the melting of the polar ice caps. Last time I checked, it was the thermal expansion of the ocean caused by its warming, with the melting of land-based ice, not the Arctic polar cap, an important secondary cause and particularly important recently.
 
7. 'Increasing atmospheric concentrations of carbon dioxide will have negligible impact on the earth’s radiation balance and will promote plant growth everywhere. There is no need to sequester CO2 in the ground or to subsidise nuclear or other non-carbon based methods of energy production.'
 
I wish I believed that, because it would make things a lot simpler. But there’s too much evidence otherwise.

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