Man-made factors are real

C Westwood comments on "those convinced that only greenhouse gases from man made activity are changing the environment".

I have never met any one who held that view or read any article on the subject putting forward that view. It is obvious from the temperature cycles the earth experienced, before man's activities could have had any effect, there must be other factors at work.

This does not mean that man's activities are not exacerbating these natural effects.

He says the fact that carbon dioxide is about half as heavy again as air explains its use as a fire extinguishing agent. There are several reasons why carbon dioxide is used in fire extinguishers but that isn't one of them.

As a by-product of some large scale chemical processes it is cheap. It can be liquefied at ambient temperature at moderate pressures; allowing relative large quantities to be stored in a small cylinder.When the Carbon dioxide discharges from the extinguisher it changes to a mixture of very cold solid and gaseous carbon dioxide.

A fire is extinguished if one side of the "Fire Triangle" is removed; the Carbon dioxide extinguisher removes two sides, the heat and the oxygen. Just blanketing a real fire with gaseous carbon dioxide would temporally put out the fire but it would most likely reignite when the carbon dioxide blanket dispersed and oxygen again had access to the hot embers.

He asks: "If man creates large quantities of carbon dioxide at, or near, ground level by what natural mechanism is this heavy gas lifted vast distances through much lighter air, into the upper atmosphere?

It is over 200 years since John Dalton demonstrated that heavy and light gases will, through Diffusion, become perfectly mixed. This occurs even if you start with the heavy gas in the lower half of the container.

An understanding of how this process works requires a study of the Kinetic Theory of Gases - not a subject for a letter to a newspaper.

Obviously in the atmosphere this mixing will be greatly accelerated by winds, convection, and circulation patterns so the composition of the atmosphere is virtually constant up to about 100km above the earth.

Personally, approaching my mid-seventies with no grand children, I have little interest in Global Warming.

Unless the present rate of Global Warming suddenly accelerates, through, for example, the sudden release of methane from the oceans, my genes should have disappeared from the gene pool before Armageddon.

This may appear cynical, but it allows me to continue running my car, enjoying the occasional foreign holiday, using the central heating and eating vegetables and fruit out of season, without feeling a hypocrite.

I refuse to join those with a lifestyle which leaves a carbon footprint bigger than a Yeti chimney sweep but then claim to be concerned about the environment.

Dr Dean Evans PhD, Pedmore