Mr Walter Attwood (Letters, 4 August) claims that atmospheric carbon dioxide is now acting as a pollutant or poison and threatens the future of the planet. This claim is based on the supposition that carbon dioxide is solely or mainly responsible for changes in climate temperature and that a continued increase will threaten life as we know it.
Actual measurement of atmospheric carbon dioxide only commenced in the 1960s and prior to that has relied on proxies. The ratio of carbon isotopes in seashells has been used as a proxy for very longterm estimation of atmospheric carbon dioxide concentrations. This proxy estimates that 200 million years ago, atmospheric carbon dioxide levels were 10-fold what they are today and 500 million years ago it was 25-fold. In both circumstances, we know from the fossil record, life burgeoned. Such observations do query the accuracy of model predictions of future climate temperature and planetary health based solely on carbon dioxide increase.
(Professor) Tony Trewavas FRS FRSE
Scientific Alliance Scotland
North St David Street