Oceans absorb the lion’s share of emitted carbons and associated heat. According to the linked article:
The world’s oceans are warming at a quickening rate, with the past 20 years accounting for half of the increase in ocean heat content that has occurred since pre-industrial times, a new study has found.
The study suggests that the heat increase along with a concomitant rise in ocean acidity threatens marine species, in particular coral.
Most alarming, I should think, is what happens when the oceans reach their absorption tipping point. The excess heat caused by fossil-fuel combustion has no other place to go than in the atmosphere. Temperatures would then rise at an even greater rate than present. And keep in mind that 2015 was the hottest year on record—since 2014.