On carbon dioxide
Discussion on climate change gives the impression that carbon dioxide is a pollutant. It is not a pollutant. Nitrate assimilation was slower under elevated than ambient CO and this affect food production. The word pollutant refers only to substances which do not occur naturally in the atmosphere. There is a distinction between saying that CO will affect nitrogen assimilation and labelling CO as a pollutant. This distinction must be kept in mind while interpreting scientific results.