This is my current understanding: Ocean acidification is the result of atmospheric $\ce{CO2}$ dissolving in the ocean's water. When this occurs the $\mathrm{pH}$ of the ocean decreases (from the increase in $\ce{H3O+}$ ions produced from the dissociation of $\ce{H2CO3}$). When there is an increase in temperature, the solubility of carbon dioxide decreases which results in a lower concentration of carbonic acid (the formation of carbonic acid is from the reaction of $\ce{CO2}$ with $\ce{H2O}$ which is exothermic, so the reverse reaction is favoured). So since the concentration of carbonic acid is lower, the concentration of $\ce{H3O+}$ ions decreases (lower concentration of acid dissociates in the water). Therefore, the $\mathrm{pH}$ of the ocean increases as there are fewer $\ce{H3O+}$ ions present in the water.
Is my understanding correct, or have I made a mistake in my explanation? If you can help me out I would be very grateful :)