Climate change packs a one-two punch for coral reefs

A guest blog by Marah J. Hardt

We’ve been blogging recently about our work in Jamaica, studying the effects of climate change on tropical sponges.  In this entry, we’re taking a step back to talk about how climate change is threatening coral reefs in general, and what you can do to help turn the tide.

When delegates gather from around the world next week in Copenhagen, the fate of entire nations and ecosystems, especially coral reefs, literally rests at their fingertips.  The United Nations Convention on Climate Change (COP15) is the only platform upon which an international treaty strong enough to tackle this global problem can be drafted and signed.   The good news is that diverse countries, including many small island states and the Commonwealth nations (representing over one third of the world’s population), are joining together to call for strong action.  The problem is, some of the most important (read: biggest polluting) countries, including the USA, are pushing for the COP15 to be simply a planning session.  Such posturing is pretty disturbing; climate change is accelerating along the “worst-case” scenario predicted by scientists and countries already have had over 5 years to “plan” for this meeting.  What the planet needs now, and coral reefs depend on, is strong commitment to immediate and drastic cuts in carbon dioxide (CO2) emissions.

Carbon dioxide is the culprit behind the two greatest impacts climate change delivers to coral reefs: warmer temperatures and changing ocean chemistry.  More carbon dioxide in the atmosphere—the result of people burning too many fossil fuels (coal, gas, and oil)— traps more heat from the sun, enhancing the greenhouse effect and warming the planet.  And a warmer planet means warmer seas.  Like all animals, corals have certain preferred temperature ranges where they live. But unlike many animals, corals live right up against their maximum temperature limit—raise the heat by 1 or 2°C and they stress.  The result—mass bleaching, followed often by mass mortality.

Bleached coral, Agaricia sp.

But it’s not just the heat corals need fear from CO2.  More CO2 in the sky means more CO2 absorbed by the ocean, which in turn causes a chemical chain reaction in the water.  The result is an ocean with a lower pH (ocean acidification) and lower supplies of carbonate, a critical building block for coral skeletons (and shells of other animals like pteropods and clams).  Less carbonate means it’s harder for corals to build new skeletons and maintain their old ones.  Scientists predict that if carbon dioxide reaches 450 parts per million(we’re at about 390 ppm now), coral reefs will start to dissolve.

Close up of coral, Meandrina meandrites, showing skeletal structure and living tentacles.


To save corals, we’ve got to bring carbon dioxide back down to 350 parts per million (ppm)—the concentration scientists deem safe not just for corals, but for the planet.


The COP15 meeting is the title fight for the future of low-lying nations and coral reefs that are running out of time.  We’ve entered the ring and climate change is advancing upon coral reefs with a swift and fierce one-two punch. The time for talking strategy is over. We’ve created this beast, so it’s up to us to reverse the momentum.  The good news is that while President Obama and other major world leaders may not be lacing boots up yet, thousands of citizens and organizations around the world are entering the fight, including religious leaders like Ecumenical Patriach Bartholomew and international organizations such as the World Association of Zoos and Aquariums.  And you can help.  Check out to see how to join in a vigil midway through the CO15 talks. Put pressure on our leaders to responsibly and effectively address climate change. Let your voice be one of the ones that helps turn the tide in favor of coral reefs and all the life and livelihoods they support.

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