Climate change and ocean acidification (OA) are large−scale threats for coral reefs, yet despite a growing literature on the effects of temperature and pCO2 on reef corals, few studies have attempted to forecast the effects at a population level. According to projections, seawater pH will decrease 0.3 to 0.4 by the end of the 21st Century, and temperature in tropical seas will be 3.2°C warmer. Using empirical analyses of the effects on respiration, survival, and calcification of early life stages of Pocillopora damicornis, we employed a demographic approach to forecast the consequences of climate change and OA on the population dynamics of this coral. Such approach can supply useful tools to forecast population dynamics under different environmental conditions. We constructed a size−based demographic model using life−history tables and transition probabilities for a population of P. damicornis in southern Taiwan and projected the population structure over 100 y under differing scenarios. The simulations incorporated a decline of larval survival due to increases in temperature and pCO2, with the results suggesting that an increase of pCO2 from 380 to 900 ppm could lead to a non−linear reduction in population density from 11.6 to 2.3 colonies m−2 in 150 y. In the first 130 y population density remains 10.6 colonies m−2, but thereafter declines quickly to 2.3 colonies m−2 by 2162. A temperature increase from 26.4°C to 29.6°C could further reduce density to 2.1 colonies m−2. The drastic decrease happens when larval survival reduce to 80%, suggesting early life stages can play an important role in the population dynamics of this species. Our model can be expanded to a metapopulation approach linking multiple populations using a connectivity matrix including empirical estimates of larval dispersal under future climate conditions