Humans are pumping more and more greenhouse gases into the atmosphere. That’s trapping excess heat and causing the surface of the planet to warm. However, surface warming accounts for only about 7% of the excess heat our planet is taking on. The other 93% goes into the oceans, setting the stage for more extreme storms, rising sea levels, melting sea ice, and a host of other impacts.
One of the most visible impacts of higher ocean temperatures is coral bleaching. Coral reefs are ecosystems that serve several important societal purposes — protecting coastlines, supporting fisheries, and drawing tourism dollars globally. When ocean temperatures get too high, the symbiotic relationship between corals and their algae becomes disrupted. During a bleaching event, the coral expels the algae, depriving the coral of both color and nourishment. The starving coral then turns white and is more susceptible to disease, and ultimately, death.
We are currently experiencing the third — and by far the longest — global coral bleaching event the world has ever seen. The 1998 El Niño sparked the first event, the second came during the 2010 El Niño, and the current bleaching, which began in 2014, will likely continue into 2017. The latest surveys show that 93% of the Great Barrier Reef has suffered from bleaching, and 35% of corals have been killed. In addition, recent research found that climate change made this bleaching event 175 times more likely.
In addition to taking up heat, the oceans also play a key role in absorbing carbon dioxide from the atmosphere. About one quarter of all excess carbon dioxide emitted to the atmosphere is taken up by the world’s oceans (and half of that absorption happens in the Southern Ocean). As it dissolves, it reacts with water and produces carbonic acid. The process depletes the ocean of carbonate ions, which many organisms, including corals, use to build shells and reef structures. Too few carbonate ions means too little food for other sea life and a lack of material to build coral reefs.