It is possible to argue that discussions of global warming have got out of control in recent months, not just in the media, but within the academic and political arenas, too. But, even if there are exaggerations and examples of hyperbole, there still has to be a baseline position from which a case for optimism can be made. How far can one go with scepticism about GW?

I have done a bit of the required reading – even as far as some of the mathematics – and it is reasonably clear to me that, when it comes to some of the alternative explanations for GW, the numbers really don’t add up; and this isn’t the models’ numbers, its the observed data. Whilst it is possible to argue attributions of warming, it is not really feasible to argue that there hasn’t been a warming trend over the last thirty-five years and, beyond that, over the last hundred. Even if the temperature measurements were all wrong, they are wrong in the same way and show the same trend. Apart from the coincidence that would imply, plus the underlying implication that scientists are incompetent, we’d then have to face the fact that other ‘symptoms’ of warming; ice loss, glacial melt, regional temperature changes, droughts, all show the same general trend. My argument then would be that we have to accept that it has warmed in modern times.

In addition, when I say that ‘it isn’t solar variation’ or ‘it isn’t volcanoes’, these observations are based on the known relationship between measured variations in such forcings and measured variations in temperatures. no models, no assumptions, simple fitting of data to data. If, on top of this, we then posit the hypothesis that at least some of the measurements of some of the variables tend to underestimate them systematically, which is at least a plausible argument, then one possible conclusion we can reach is that the measured forcing of CO2, calculated in relation to these other forcings, may be exaggerated. Because of the physics, I can’t see how it can be eliminated completely as a forcing, however.

Then there comes the issue of climate sensitivity. This is a heavily mathematical/statistical field of research and I simply don’t have the background to critique methods and formulae. I can, however, follow arguments and challenge conclusions. It is in areas like this where I tend to follow the lead of specialists, who not only can do what I cannot, but also offer what I judge, based on my knowledge of logic, to be reasoned and balanced judgements.
As things stand, these specialists have narrowed down the range of equilibrium climate sensitivity (response to a doubling of CO2) to 2-4.5C, very unlikely less than 1.5C, unlikely more than 5C. Most of the main players work with a figure between 2.5 and 3C. Even if their work is based on an exaggeration, it is still hard to reach a climate sensitivity figure below 1.5C.

So,  an individual who was cynical about many of the claims, and dubious about some of the figures offered, can reasonably argue that temperatures are as likely to rise by only 2C as they are by more, if CO2 levels are doubled. Pushed hard, a case might be made for only 1.5C.

But then comes the big political issue; under what circumstances are CO2 emissions limitable to 550ppm? (the doubling). How much CO2 are we going to pump into the system, and how quickly? These are not questions of climate science at all, but political matters, and depend on human actions and decisions, not on how the climate works.

Has it warmed? Is some of the warming human-induced? Is some of the warming able to be fitted into natural variations and forcings? Here, I suggest that the answer to all of these questions must be ‘Yes’. The challenge for the sceptic, if this is the case, is to demonstrate that the human component of climate change is less than has been suggested, and not sufficient to merit undue concern.