It is expected that [CO] will reach 500–1000 ppm by 2100. 96% of the past 400,000 years experienced below 280 ppm CO. From this figure, it is highly probable that genotypes of today’s plants have diverged from their pre-industrial relatives.
The gene HIC (high carbon dioxide) encodes a negative regulator for the development of stomata in plants. Research into the HIC gene using Arabidopsis thaliana found no increase of stomatal development in the dominant allele, but in the ‘wild type’ recessive allele showed a large increase, both in response to rising CO levels in the atmosphere. These studies imply the plants response to changing CO levels is largely controlled by genetics.