Climatide

flickr/Cybersam

This year’s record-high temps have come record-high energy use for air-conditioning. But at least we have a way to cool off. Not so for the world’s coral reefs. And for all that they live in the tropics, corals don’t take kindly to overheating.
Corals hold millions of tiny algal cells within their bodies. They give corals their brilliant colors, but also generate the sugars corals need to survive. When high temperatures stress corals, they eject their colorful algal chefs in a phenomenon known as bleaching. The New York Times reports today that we are in the midst of the second global coral bleaching event ever (the first was in 1998, the year that ties this year for record-high air and sea temperatures).

From Thailand to Texas, corals are reacting to the heat stress by bleaching, or shedding their color and going into survival mode. Many have already died, and more are expected to do so in coming months. Computer forecasts of water temperature suggest that corals in the Caribbean may undergo drastic bleaching in the next few weeks.

What is unfolding this year is only the second known global bleaching of coral reefs. Scientists are holding out hope that this year will not be as bad, over all, as 1998, the hottest year in the historical record, when an estimated 16 percent of the world’s shallow-water reefs died. But in some places, including Thailand, the situation is looking worse than in 1998.

Scientists say the trouble with the reefs is linked to climate change. For years they have warned that corals, highly sensitive to excess heat, would serve as an early indicator of the ecological distress on the planet caused by the buildup of greenhouse gases.

Rising temperatures aren’t the only way greenhouse gases threaten corals. As carbon dioxide builds up in the atmosphere, likewise in the ocean. Carbon dioxide plus seawater forms carbonic acid and the pH balance of the ocean moves toward the acid end of the scale. It’s a process known as ocean acidification and some experts call it climate change’s evil twin.

I recently sat down with Susan Avery, Director of Woods Hole Oceanographic Institution, for a long conversation about the challenges facing the ocean today. She says it’s a toss-up whether rising ocean temperatures or ocean acidification will get to corals first.

Corals will respond to temperature increases, and we’ve seen that before … But they seem to recover from that. It’s not clear that they will recover from ocean acidification.