I am pleased that my Gresham Lecture on the Mathematics of Climate Change has provoked such an active debate and I wanted to respond to some of the comments

The purpose of the lecture was to show how mathematical models are used to help explain past climate changes and to predict future climate changes.

“The climate has always changed – so the latest changes are not important”

A number of the comments have made the point that climate has always changed in the past, and a major driver of this is variations in the amount of solar energy reaching the Earth, caused in part by orbital changes of the Earth, the kind of things seen during the ice ages. That’s true, but unfortunately, such issues are already fully taken into account in all of the climate models that are used. In other words we can’t dismiss them on that basis.

In the shorter term, the changes we are currently seeing in the climate, are occurring much faster than the variations in solar activity caused by orbital variations. Furthermore the current solar activity shows a small decrease in recent years. On the other hand the effect of Carbon Dioxide on short term change is extremely important.

“The science about carbon dioxide driving global warming is not conclusive”

The relation of atmospheric Carbon Dioxide to temperature, caused by its transmission and absorption of long and short wave radiation, is well-documented. The science that underlies this effect has been established for over 100 years, and the evidence that Carbon Dioxide is driving the recent warming is conclusive. The simple model that I present towards the end of my lecture shows some of the scientific reasoning behind this and allows us to quantify the impact of the changes in Carbon Dioxide in the atmosphere. More complex models, such as those used by the many climate centres, give a more precise quantification of this, as well as estimating the uncertainty in the different predictions.

“The mathematical models are not accurate enough”

Contrary to various of the comments made, the current climate models based on sound physical principles, encoded as mathematical equations, do give reasonably good predictions of what is observed, and this can be seen in the many papers published in the scientific literature.  They really do give us the best way of understanding what the future impact of changes in, for example, the amount of Carbon Dioxide, will have on our future climate. As such they form an important part of the debate on climate change.