Rising atmospheric carbon dioxide (CO₂) concentration can change crop productivity directly by increasing photosynthesis, and indirectly by positive or negative modifications of growth responses to predicted global warming and changes in rainfall. The purpose of this experiment was to determine the effects of CO₂, temperature, soil type, and water table depth on growth of four cultivars of sugarcane, a C₄ photosynthetic pathway species (Saccharum officinarum L.). Studies were conducted in paired temperature-gradient greenhouses at ambient and enriched levels of CO₂ [≈ 360 and ≈ 710 μmol (CO₂) mol^-1 (air), respectively, or ppm, mole fraction basis] with four temperature zones along the length of each greenhouse: baseline, +1.5, +3.0, and +4.5°C. These 1.5°C steps were maintained by a combination of heat inputs (electric heaters and sunlight) and ventilation by computer-controlled fans. Other treatments were soil type (mineral vs. organic), water table depth (constant water table of 20 cm vs. ≈50 cm drained profile). The four cultivars were CP72-2086, CP73-1547, CP88-1508, and CP80-2086.  Of the first sampling in late June-early July of 1997, doubled CO₂ increased the following components of plant growth: leaf number, 7%; leaf area, 15%; leaf fresh weight, 13%; leaf dry weight, 8%; mainstem length, 32%; mainstem fresh weight, 31%; mainstem dry weight, 23%; juice volume, 40%; total fresh weight, 25%; juice dry weight, 36%; total dry weight, 21%. However, total fresh weight increase of that whole-crop harvest was somewhat less at 16%. Increasing temperatures caused a slight downward trend in sugarcane yield regardless of cultivar or CO₂ treatment. The order of cultivar yields for the first harvest was: CP73-1547 > CP80-1827 > CP88-1508 > CP72-2086.  Doubling CO₂ appeared to benefit sugarcane productivity more than the anticipated 10% increase for a C₄ species. The apparent increases in sugarcane dry weight, fresh weight, and juice volume indicate greater yields as global atmospheric CO₂ continues to rise. Particularly, the production of stem juice and sugar appeared to respond more to CO₂ enrichment than did the plant biomass. This important finding would mean that productivity of the C₄ sugarcane should be enhanced by future rises in atmospheric CO₂.