Atmospheric p CO 2 is predicted to rise from 400 to 900 ppm by year 2100, causing seawater temperatures to increase by 1-4 °C and pH to decrease by 0.1-0.3. Sixty-day experiments were conducted to investigate the independent and combined impacts of acidification ( p CO 2 =425/915 ppm) and warming (T=28/32 °C) on calcification rate and skeletal morphology of the tropical scleractinian coral Siderastrea siderea. Coral calcification rate was negatively impacted by warming and acidification, with their combined effects yielding the most negative impact. Effects of warming and high-temperature acidification on calcification rate were apparent across both 30-day observational intervals of the experiment, while effects of low-temperature acidification were not apparent until the second observational interval. Corallite height and infilling were negatively impacted by acidification, but not significantly (p>0.05) impacted by warming. These results suggest that S. siderea will grow more slowly and accrete weaker skeletons in warmer, more acidic oceans predicted for the future.