Global average atmospheric CO2 concentrations are predicted to double before the end of this century. This increase has been predicted to raise global average temperatures, which in turn will increase atmospheric humidity. How plants will respond to these changes is an area of intense study. The variation within ecotypic responses of Arabidopsis thaliana to these environmental variables (C02, temperature and humidity) is explored in this thesis using a combination of morphological and novel environmental metabolomics techniques. This study utilises ecotypes of Arabidopsis thaliana originating from a range of altitudes and geographical locations to elucidate altitude-mediated variation In response to changes In environmental conditions. Morphological investigation shows that stomatal conductance is regulated by an interchangeable mechanism of stomatal density and stomatal aperture over a range of CO2 treatments and that elevated temperature or humidity can disrupt this mechanism. Furthermore, these characteristics of stomatal responses of Arabidopsis thaliana are shown to be independent of ecotypic altitude of origin. Environmental metabolomic analysis demonstrated clear separation between ecotypic rnetabolite fingerprints as well as showing correlations between ecotype altitude of origin and specific plant primary and secondary metabolites; providing novel elucidation of biochemical pathways involved in responses to environmental perturbation.