From Chris Crowe
In applying Karl Popper’s philosophy of science, Roger James implies that only a falsifiable hypothesis is a scientific one, and that theories linking such things as greenhouse gas emissions to climate change are “outside science” (14 April, p 23). There are, however, other measures of a theory beyond Popper’s.
The science of epidemiology, for example, hypothesises links that cannot be tested in a Popperian framework.
It is well accepted that smoking causes lung cancer, despite instances of lung cancer in people who have never smoked, and smokers who never succumb to lung cancer.
Legal systems introduce burdens of proof. In British criminal law, conviction requires that defendants be guilty beyond any reasonable doubt; in civil law, issues are decided on the balance of probabilities.
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Where does climate change sit? Where does smoking sit?
There are expert witnesses on both sides, but the preponderance of scientists knowledgeable in these subjects have lined up to say that smoking causes cancer, and man-made greenhouse gas emissions are contributing to climate change.
I wouldn’t say that the climate change case is proven beyond a shadow of doubt, but surely it is proven on the balance of probabilities. This level of proof has been sufficient for governments to exert some control over tobacco companies, and it should now be sufficient for governments to institute controls on climate-affecting industries.
From Gregory Bradley
The test lies in the name of the phenomenon: “greenhouse effect”. All it would take to falsify it is an experiment conducted under controlled conditions that did not produce a temperature rise resulting from adding accepted greenhouse gases into the atmosphere.
In fact, all such experiments have shown a greenhouse effect.
In addition, we know humans are releasing large amounts of greenhouse gases; our measurements show levels of greenhouse gases in the atmosphere to be rising; and temperatures are also rising.
All these factors tally with the theory being true, so the onus of proof would seem to be on those proposing alternative explanations for the heating to explain why the additional greenhouse gases are not causing it.
Man-made greenhouse gas emissions are the simplest explanation for the observed phenomena.
Logan, Queensland, Australia
From Martin Parkinson
Climate scientists are proper scientists; they have heard of falsifiability; there is no growing body of evidence throwing doubt on man-made warming.
Bristol, UK
Perth, Western Australia
