Roy Turnbull (Letters, 13 January) makes some pertinent points about climate temperature but omits others. The IPCC gave a temperature range of 1.5-4.5C for CO2 doubling based on complex models. Which temperature is chosen by any individual reflects their assessment of likely future circumstances.
However, the models have known shortcomings, most obviously the failure to predict the current temperature stasis. A recent and very simple alternative has used direct satellite measurements of the excess heat absorbed by the Earth. When cumulatively assessed over a decade and with known CO2 changes in this period, the projected temperature increase from a doubling can be estimated. With four decades now individually assessed and reported in several scientific publications, the projected temperature increase is at the very low end of the IPCC temperature range, something which would agree with the apparent present stasis. Direct observation is always scientifically preferable to models.
(Prof) Tony Trewavas FRS FRSE
Scientific Alliance Scotland