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The biomass of plants for the purpose of phytoremediation is often small. Carbon dioxide (CO2) can enhance plant biomass and so, it is reasonable to draw such an assumption that CO2 can be used to help plants to phytoremediate heavy metal contaminated soils through enhancing the biomass of remediating plants. To identify this assumption, a micro-plot study in six separate growth chambers was conducted to investigate the effect of high CO2 levels (approximately 1000?±?50?µL?L?1) on Cu accumulation and the remediation potential of three rape varieties and another five crop and pasture species grown in soils contaminated with Cu (485?mg?Cu?kg?1, denoted as soil-L, and 1200?mg?Cu?kg?1, denoted as soil-H). The results showed that independently of the CO2 treatment, the shoot biomass and Cu concentration in the eight plants varied with the species and soil Cu levels. The plants grown in soil-L produced a higher aboveground biomass than those grown in the more heavily contaminated soil-H, but the Cu levels were high in all the plants grown in soil-H. Regardless of the CO2 treatment, the shoot biomass and Cu concentration in the plant parts also varied with the species and soil Cu levels. Overall, the exposure of all the plants to elevated CO2 resulted in a biomass increase of 6–136% and a significantly higher remediation capacity. The results indicate that the ever-increasing atmospheric CO2 may enhance the phytoremediation efficiency of Cu contaminated soils; however it also suggests a risk of food safety under the future scenario of elevated atmospheric CO2.