SIR – Noel Shaw (Letters, January 13) is right to state that climate is primarily caused by the sun and that carbon trading is an opportunity for the market to make money rather than reduce the level of CO2.

However, the sun doesn’t wax and wane – it was relatively cool when the earth began more than four billion years ago and it has become steadily hotter. In due course it will consume itself and us. Despite this, there is some variation with it being very slightly hotter if there are more sun spots, and the number varies on an 11-year cycle.

At the moment such extra activity is at the lowest it has been since records began a number of centuries ago, so another mechanism is needed to explain why 2010 was the equal-hottest year in human experience. Man-made warming, through the introduction of fossil fuel C02, is the only scientific explanation that fits the observed data, and this is supported overwhelmingly by academics of the appropriate science.

The coal and oil industries are threatened by these findings and so support a small number of scientists and websites to query them and delay the action that will reduce their profits.

Keith Thomson, Heights Lane, Bradford