I continue to find the artificial debates (SPATalks) of SPA more akin to a Punch and Judy display than to serious contribution to resolution of complex issues. 

The latest example is provided by the discussion of climate change and aviation (SPA March 2008). Would it not be more satisfactory for the combatants to agree upon a few fundamental features to illustrate the consequences of different approaches and to forego spread-shot point-scoring? In this particular example, one contestant starts from an assumption of extrapolation from current practices and demands – not a very realistic stance for a rapidly changing world – while the other restates attitudes without context. The prerogative of perpetual growth was confined to a privileged minority in a finite world, no longer our status for future planning.

For a start, we would need to agree the fundamental basis for measurement of CO2 emissions, which seems currently obscure. The only equitable and ‘transparent’ basis would be to establish the total release to atmosphere by ‘UK Ltd’, that is, that directly and indirectly attributable to the United Kingdom. What we import would be ‘charged’ for its CO2 emissions arising from production and transport. What we export would be likewise deemed a credit to UK.

This would provide a basis for passenger and freight movements by air and other means. Otherwise, it is all too easy to shift responsibility for our emissions on to others.

Several percentages were quoted without establishing their context. Looking towards the future, for example, a present day contribution of n per cent, where n is a fairly small figure, would correspond to 5n per cent when CO2 emissions overall had been reduced by 80 per cent.

(Sir) Alan Muir Wood Pangbourne Berks