This presentation introduces two of the main threats that climate change poses to the survival of coral reefs: ocean acidification and bleaching events due to global warming.

1. Coral reefs:
how they are impacted by climate change,
and why it matters.

2. What are coral reefs ?
Coral reefs are underwater calcium carbonate formations
secreted by corals.
Corals are quite remarkable. They are
constituted of colonies of genetically
identical invertebrates, with an
exoskeleton. “Most corals obtain the
majority of their energy and nutrients from
photosynthetic unicellular algae that live
within the coral's tissue
called zooxanthella” (Source: Wikipedia).
A coral reef thus associates animal,
vegetal and mineral elements.
Florida Keys National Marine
Sanctuary (CC – NOAA - Commander
William Harrigan, NOAA Corps (ret.))

3. CO2 emissions and ocean acidification
Oceans absorb a large quantity of human activity related CO2
emissions. This causes the formation of carbonic acid, which
increases the level of acidity of oceans.
Oceans have absorbed about 30 % of CO2 through direct
chemical exchange.
“Since 1750, the pH of the ocean’s surface has dropped by 0.1,
a 30 percent change in acidity.”
(Source: NASA -http://earthobservatory.nasa.gov/Features/
CarbonCycle/page5.php)

4. Ocean acidification: a serious threat to corals
Because the exoskeleton of coral polyps are based of calcium
carbonates, it is very sensitive to level of acidity levels.
The 2012 World Bank report “Turn Down the Heat: Why a 4°C
Warmer World Must Be Avoided” states:
“If atmospheric CO2 reaches 450 ppm, coral reef growth around
the world is expected to slow down considerably and at 550 ppm
reefs are expected to start to dissolve. (…) A CO2 level of below
350 ppm appears to be required for the long-term survival of coral
reefs (…).”
The currently level of acidity is about 390 ppm.
Source: World Bank. 2012. Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided. Washington,
DC. © World Bank, pp. 24-26 https://openknowledge.worldbank.org/handle/10986/11860

5. Possible impact of acidification on corals
Most CO2 emissions projections imply that increasingly threaten
the survival of coral reefs.
Diagram from:
World Bank. 2012. Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided. Washington, DC. ©
World Bank., p. 26 (Based on Hare et al. 2011; Rogelj et al. 2010; Schaeffer et al. 2012.)

6. What is coral reefs bleaching?
To learn more about the phenomenon of coral bleaching, we
invite you to watch a short Youtube video from the
ClimateXchange network: http://youtu.be/60jof35WuAo

7. Increased risks of bleaching events
Climate change is likely to induce more frequent episode of
unusual temperature variations, which are the cause of
bleaching events.
“In fact, frequency of bleaching
events under global warming
in even a 2°C world has been
projected to exceed the ability
of coral reefs to recover.”
(Source: Turn Down the Heat: Why a
4°C Warmer World Must Be Avoided.
Washington, DC. © World Bank,p.52)

8. Scenarios
Current climate change
scenarios are a call for
action.
Even with global
warming limited to two
degrees Celsius, most
coral reefs are at risk of
definitive disappearance.
Detail of an infographic
by: World Bank/
CC BY-NC-ND license http://goo.gl/7JP6Tp

9. A world without corals?
“Why should we care about coral reefs anyway? Beyond their
clear aesthetic values, they are hotspots of biodiversity. But,
they actually support over 500 million people worldwide, and
about 30 million people depend entirely on coral reefs because
they actually live on them.”
Dr. Janice Lough - “Turn Down the Heat” week 3 lecture.
Photo: Margaret Wertheim.
CC Attribution 2.0 Generic License.

10. Losing corals reefs would be dramatic for
marine ecosystems and humans who
depend on it.
Yet, corals are already under threat and even limited global
warming of 2 degree Celsius could jeopardize most coral reefs
future.
We must act now, through our individual
action, consumption, communication or vote,
to rapidly reduce CO2 emissions!

11. Coral reef ecosystem at Palmyra Atoll National Wildlife Refuge
Creative Commons: Jim Maragos/U.S. Fish and Wildlife Service Source: Flickr

12. To learn more about coral reefs and
climate change:
US National Oceanic and Atmospheric Administration – Coral reef
conservation programme
http://coralreef.noaa.gov/
Center for Ocean Solutions
http://centerforoceansolutions.org/climate/impacts/
World Bank. 2012. Turn Down the Heat: Why a 4°C Warmer World Must Be
Avoided. Washington, DC. © World Bank.
https://openknowledge.worldbank.org/handle/10986/11860
The international Panel on Climate Change – Fifth Assessment Report
(AR5) – Work Group 1
https://www.ipcc.ch/report/ar5/