The first of the skeptical viewpoints mentioned in the Prelude denied that there was such a thing as climate change – I referred to this as NCS. I said that this was not on the face of it, a defensible position, which suggests that we should perhaps just dismiss it straight away and move on to address less implausible views. However, it is worth seeing what someone who adopts NCS is committed to and how her position could be defended. What she is committed to depends on precisely that she is denying, and given what we have said about climate change and how it is defined, it turns out that there are three possibilities. One of these directly challenges irrefutable scientific evidence, another simply dodges the issue by refusing to allow any definition of climate change, but the third is more difficult to dispose of.

 

On way to deny climate change is to reject the suggested definition of climate change given in the second of these posts, namely:

 

Climate Change (CC): Climate change occurs when there is a persistent change in the weather which is caused by corresponding (unidirectional) change in the underlying determinants of the weather, such as temperature.

 

Thus NCS denies that climate change is a persistent change in the weather driven by changing (normally, increasing) global temperature. It is possible for NCS to come up with her own definition of climate change, but unless this makes reference to persistent change in the weather, due various underlying physical parameters, it will not be worth taking seriously. It seems unlikely that any such definition will be too much at odds with CC, but I leave this possibility for later discussion. So unless NCS can up with a reasonable view about what climate change is, then denying it exists become a matter of fiat: whatever climate change is, it is not happening.

 

This is not a reason for denying climate change. To deny that something is true, in any meaningful way which allows debate and discussion, what is being denied must be described or specified in some way. To say “I deny X, whatever X is” is not to make any kind of an informative statement which can form a basis for further discussion. This is not therefore a response to the question that we should take seriously. Suppose NCS accepts CC but still denies that there is actually climate change. This might appear to be contradictory: by accepting CC, is NCS not committed to accepting climate change? No, because CC is a (proposed) definition of climate change and not an assertion to the effect that climate change is actually happening. However, CC together with an assertion that the average global temperature is increasing does imply that the climate change is taking place.

 

The first and most obvious way that NCS could accept CC and deny that there is any actual climate change is therefore to claim that the Earth’s temperature average temperature has not risen, above, say, pre-industrial levels. But scientists are (all but) unanimous that it has, and hence NCS is committed to skepticism about a claim that the overwhelming majority of scientists accept. We need to examine this issue is a bit more closely. The average global temperature is determined by measuring the temperature values at multiple locations on the Earth’s surface, and then taking the average. Clearly, the more locations that are included and the more reliable the measurement techniques, the more accurate the global temperature estimate. I will not go into any great detail about how this is done. But in the case of easily accessible terrestrial locations, temperature can be measured by using one of a number of standard techniques, such as a mercury thermometer, at points in the centre of the cells of a  grid covering the Earth’s surface. At sea this could be (and sometimes still is) done by hauling up buckets of water and measuring their temperature.  All in all, a difficult and time-consuming process, which would inevitably entail some extrapolations. Nowadays, the readings are done by satellite – by techniques I will not go into – while the older methods are used as a basis of comparison, and the agreement has turned out to be very good.

 

To deny that the average global temperature has risen since pre-industrial time is to deny that some or all of these techniques work. But all such techniques are ‘guaranteed’ to work by scientific theories and principles – the techniques are ‘embedded’ in theory. For instance there is a principle of the science of thermodynamics which states that all liquids expand when heated. This is the basis of all thermometer temperature measurements. To dispute that temperatures measuring with a mercury or alcohol thermometer are wrong is thus to call into question the theory of thermodynamics. Thermodynamics is a very reliable theory, and moreover one that underlies other practical matters besides temperature measurement, and to be committed to a position which entails that it is not reliable is thus not one that we can take seriously. And of course we could challenge NCS to tell us how she would measure temperature.

 

NCS could admit that there has been an increase in the underlying  temperature, but deny that this has had any effect on the weather. This is not to deny the possibility of global climate change because we are assuming NCS accepts CC and hence that temperature is the driver of climate change. Accepting CC as the definition of climate change, accepting that the global temperature has increased since pre-industrial times but denying that there has been any climate change, together imply that this increase in temperature has not been enough to cause “persistent change in the weather”. In other words, NCS can simply deny that there is, or has been, climate change, while leaving open the possibility that there could be (if only the temperature rose sufficiently). In this case, NCS must dismiss all the apparent instances of changes in the weather as being due to ‘natural’ variations.

 

This is a standard tactic for a whole range of climate sceptics. For example, at the time of writing, terrible bushfires are consuming great tracts of our native forests in Australia, bushfires that are far worse that at any time in the past. The immediate cause of any fire is what ignites it, be it lighting strikes, fallen power lines or people. For a fire to burn, there has to be fuel and there is a great deal of it in Australia because of a very prolonged drought. Climate change deniers have focused on these two issues, some even blaming arsonists, and have denied climate change is the cause of the fires. However, the drought itself has a cause, namely changes in the Indian Ocean dipole and the ENSO, as we have seen. And finally, these changes in ocean temperature themselves do not occur spontaneously  - they too have a cause.

 

I will come back to ideas about causes, proximate causes, background conditions, and so forth later: they need to be disentangled and clarified, otherwise they can be the object of deliberate obfuscation. However, this third response by NCS  represents a challenge for climate scientists, namely to show just how rising global temperature gives rise to the manifest changes in the weather that we are experiencing, such as the crippling drought in Australia, the greater prevalence of category five hurricanes in the Atlantic, and so on. These are complex problems.

 

So to conclude, I have considered three ways in which NCS can deny that the climate has changed. The first way, one that simply closes off any debate or discussion, is to refuse to accept CC or any other definition of climate change. The second is to deny that the global temperature has changed. Both of these responses should not be taken seriously. But the third should be: it is that despite apparent evidence to the contrary, increasing global temperatures have not caused climate change. We will need to come back to this question.