It is difficult for any of us to decide where the truth is most likely to lie when supposed experts disagree. This is especially the case where a high degree of scepticism is an essential component of the scientific method.
We could attempt to understand the basis of the arguments and then draw our own conclusions. In the case of global warming this is perfectly possible as the key indicators are easy enough to grasp.
However, in practice most of us have to rely on the consensus of the experts to help us decide — that, in fact, is the function of the International Panel on Climate Change (IPCC).
It looks at the peer reviewed scientific evidence across the whole spectrum of relevant scientific disciplines. It draws conclusions based on this evidence and sets limits to the degree of certainty to be given to those conclusions — in complete contrast to what journalists normally do.
The recent IPCC report states, with 90% certainty, that the increase in average global temperatures over the past half century is due to human induced releases of greenhouse gases, notably but not exclusively CO2. This is far from ‘science by consensus, hysterical or otherwise’ — there is in fact no such thing.
The climate sceptics quoted by Ryle Dwyer are playing games with the evidence. For instance, he quotes Piers Corbyn as arguing that “none of the major climate changes in the past thousands of years can be explained by CO2”.
Nobody claims they can be.
The consensus among the scientific experts is that the eight major ice ages (as shown by ice cores from the Greenland and Antarctic ice fields) over the past 800,000 years were driven by the 100,000-year variation in the shape of the earth’s orbit around the sun and by the 42,000-year variation in the tilt of the earth’s axis.
It may surprise people to know that during summer in the northern hemisphere, the earth is further from the sun and when the axial tilt is at its maximum, then the amount of sunshine reaching the earth at high latitudes is reduced. The snow does not melt in the summer and hence an ice age gets underway.
Ryle Dwyer quotes Ian Clark as saying “you can’t say that CO2 will drive climate — it never did in the past”.
Logically, this is nonsense. All the experts agree that CO2 was not the primary forcing agent in the three major ice ages of earth’s history, although most would argue that CO2 played a significant role in various feedback mechanisms.
The whole point is that the increase in CO2 concentrations since the industrial revolution is unprecedented — we know that during the eight interglacials over the past 800,000 years, CO2 levels never rose above 280 parts per million (ppm), but are now at 380 ppm with a change from 315 ppm over a 60-year period.
We know why they have risen — we have burned fossil fuels and made cement at record levels. We know that if the oceans had not absorbed more than 40% of the human induced CO2, the levels would be much higher.
We know that the sun’s energy output varies slightly but insignificantly over this timeframe. There is no evidence that sunspot activity, supposedly effecting cloud-making by way of condensation nuclei from cosmic rays, is significant. The evidence is that the average cosmic ray flux was constant over the past half century.
Ryle Dwyer says “scientists have detected that the polar (CO2) ice caps on Mars are receding”. We know those polar ice caps are seasonal, but we have only been able to study them for eight years — far too short a time to draw any firm conclusions. We know far too little about the Martian atmosphere yet.
Of course the sun drives climate — whether it drives climate change depends on the circumstances. The balance of evidence in present circumstances points to human induced change because the solar cycles and disposition of the continents that drove previous climate changes cannot apply over such short timescales in the absence of any evidence of significant variability in the sun’s energy output.
A final point on the science — Al Gore may have got it wrong on the CO2/temperature relationships from the ice core data (the jury is out on the issue and the conclusion is likely to be that the interaction is dynamic and cyclical), but again it is not relevant in the current situation.
The claim by Ryle Dwyer and his sources that the IPCC are liars, charlatans and lacking in integrity is a morally bankrupt conspiracy theory. They say you should be critical of what you read in the papers — the same applies to TV programmes, only more so.