Ocean
Acidification
Summary for Policymakers

Third Symposium on the Ocean in a High-CO2 World

Scientific sponsors:
The International Geosphere-Biosphere Programme (IGBP) was launched in 1987 tocoordinate international research on global-scale and regional-scale interactions between
Earth’s biological, chemical and physical processes and their interactions with humansystems. IGBP’s international core projects Integrated Marine Biogeochemistry andEcosystem Research (IMBER), Surface Ocean–Lower Atmosphere Study (SOLAS), Past
Global Changes (PAGES) and Land–Ocean Interactions in the Coastal Zone (LOICZ) study
ocean acidification.
The Intergovernmental Oceanographic Commission (IOC-UNESCO) was established by
the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1960
to provide Member States of the United Nations with an essential mechanism for global
cooperation in the study of the ocean.
The Scientific Committee on Oceanic Research (SCOR) was established by theInternational Council for Science (ICSU) in 1957 and is a co-sponsor of the international
projects IMBER and SOLAS.

Citation:
IGBP, IOC, SCOR (2013). Ocean Acidification Summary for Policymakers – Third
Symposium on the Ocean in a High-CO2 World. International Geosphere-Biosphere
Programme, Stockholm, Sweden.

Editors:
Wendy Broadgate (IGBP), Owen Gaffney (IGBP), Kirsten Isensee (IOC-UNESCO), Ulf
Riebesell (GEOMAR), Ed Urban (SCOR) and Luis Valdés (IOC-UNESCO).

Authors:
Wendy Broadgate, IGBP; Ulf Riebesell, GEOMAR Helmholtz Centre for Ocean ResearchKiel, Germany; Claire Armstrong, University of Tromsø, Norway; Peter Brewer, Monterey
Bay Aquarium Research Institute, USA; Ken Denman, University of Victoria, Canada;
Richard Feely, Pacific Marine Environmental Laboratory, NOAA, USA; Kunshan
Gao, Xiamen University, China; Jean-Pierre Gattuso, CNRS-UPMC, Laboratoired’Océanographie, France; Kirsten Isensee, IOC-UNESCO; Joan Kleypas, National Center
for Atmospheric Research (Climate and Global Dynamics), USA; Dan Laffoley, International
Union for Conservation of Nature, Switzerland; James Orr, Laboratoire des Sciences du
Climat et l’Environnement, France; Hans-Otto Pörtner, Alfred Wegener Institute, Germany;
Carlos Eduardo de Rezende, Universidade Estadual do Norte Fluminese, Brazil; Daniela
Schmidt, University of Bristol, UK; Ed Urban, SCOR; Anya Waite, University of Western
Australia; Luis Valdés, IOC-UNESCO.
The authors thank the following people for their comments on the draft manuscript: Jim
Barry (MBARI), Richard Black (Global Ocean Commission), Luke Brander (VU University
Amsterdam and Hong Kong University of Science and Technology), Sam Dupont(Gothenburg University), Jonathan Wentworth (UK Parliamentary Office of Science andTechnology) and Wendy Watson-Wright (IOC-UNESCO).

Infographics:
Félix Pharand-Deschênes (Globaïa), Naomi Lubick (IGBP), Owen Gaffney (IGBP), Wendy
Broadgate (IGBP)

Graphic design and production:
Hilarie Cutler (IGBP), Naomi Lubick (IGBP)

Cover image:
Ocean pH in 2100. Model data from Tatiana Ilyina, Max Planck Institute for Meteorology;
map by Globaïa.

Ocean Acidification
Ocean acidification researchis growing rapidly. The Third
Symposium on the Ocean ina High-CO2 World (Monterey,
California, September 2012)
convened 540 experts from37 countries to discuss theresults of research into ocean
acidification, its impacts on
ecosystems, socio-economic
consequences and implications
for policy. More than twice as
many scientists participatedin the Monterey symposium
compared to the previous
symposium four years earlier.

Atmospheric carbon dioxide (CO2) levels are rising as a result of humanactivities, such as fossil fuel burning, and are increasing the acidity ofseawater. This process is known as ocean acidification. Historically, the ocean
has absorbed approximately 30% of all CO2 released into the atmosphereby humans since the start of the industrial revolution, resulting in a 26%
increase in the acidity of the ocean1.
Ocean acidification causes ecosystems and marine biodiversity to change.
It has the potential to affect food security and it limits the capacity of theocean to absorb CO2 from human emissions. The economic impact of ocean
acidification could be substantial.
Reducing CO2 emissions is the only way to minimise long-term,large-scale risks.

Here we present a summaryof the state of knowledge on
ocean acidification based on thelatest research presented at the
symposium and beyond.

What else can go here? or justsome photos

Katharina Fabricius

OCEAN ACIDIFICATION page 1

Summary of outcomes
During the last 20 years, it has
been established that the pH of
the world’s oceans is decreasing
as a result of anthropogenic CO2
emissions to the atmosphere.
The Third Symposium on the
Ocean in a High-CO2 World built
on this knowledge.

 The ocean continues to acidify at an unprecedented rate in Earth’s history.
Latest research indicates the rate of change may be faster than at any time inthe last 300 million years.
 As ocean acidity increases, its capacity to absorb CO2 from the atmospheredecreases. This decreases the ocean’s role in moderating climate change.
 Species-specific impacts of ocean acidification have been seen inlaboratory and field studies on organisms from the poles to the tropics.
Many organisms show adverse effects, such as reduced ability to form
and maintain shells and skeletons, as well as reduced survival, growth,abundance and larval development. Conversely, evidence indicates thatsome organisms tolerate ocean acidification and that others, such as someseagrasses, may even thrive.
 Within decades, large parts of the polar oceans will become corrosive to theunprotected shells of calcareous marine organisms.
 Changes in carbonate chemistry of the tropical ocean may hamper or
prevent coral reef growth within decades.
 The far-reaching effects of ocean acidification are predicted to impact foodwebs, biodiversity, aquaculture and hence societies.
 Species differ in their potential to adapt to new environments. Ocean
chemistry may be changing too rapidly for many species or populations toadapt through evolution.
 Multiple stressors – ocean acidification, warming, decreases in oceanic
oxygen concentrations (deoxygenation), increasing UV-B irradiance due tostratospheric ozone depletion, overfishing, pollution and eutrophication– and their interactions are creating significant challenges for ocean
ecosystems.
 We do not fully understand the biogeochemical feedbacks to the climate
system that may arise from ocean acidification.
 Predicting how whole ecosystems will change in response to rising CO2
levels remains challenging. While we know enough to expect changes inmarine ecosystems and biodiversity within our lifetimes, we are unable to
make reliable, quantitative predictions of socio-economic impacts.

Katharina Fabricius

OCEAN ACIDIFICATION page 2

 People who rely on the ocean’s ecosystem services are especially vulnerable
and may need to adapt or cope with ocean acidification impacts within
decades. Shellfish fisheries and aquaculture in some areas may be able tocope by adjusting their management practices to avoid ocean acidification
impacts. Tropical coral reef loss will affect tourism, food security andshoreline protection for many of the world’s poorest people.

Mitigation and adaptation
Policy considerations
Ocean acidification is not
explicitly governed byinternational treaties. United
Nations (UN) processes andinternational and regional
conventions are beginning
to note ocean acidification(London Convention/Protocol,
UN Convention on the Lawof the Sea, Convention on
Biological Diversity andothers). Negotiators to the UN
Framework Convention on
Climate Change (UNFCCC) havebegun to receive regular reports
from the scientific community
on ocean acidification, andthe issue is now covered in
the assessment reports of theIntergovernmental Panel on
Climate Change (IPCC).
In June 2012, the UN
Conference on Sustainable
Development (Rio+20)
recognised ocean acidification
as a threat to economicallyand ecologically important
ecosystems and humanwellbeing.
However, there are still nointernational mechanisms
or adequate funding to deal
specifically with mitigation
or adaptation to ocean
acidification.

 The primary cause of ocean acidification is the release of atmospheric CO2from human activities. The only known realistic mitigation option on a
global scale is to limit future atmospheric CO2 levels.
 Appropriate management of land use and land-use change can enhance
uptake of atmospheric CO2 by vegetation and soils through activities suchas restoration of wetlands, planting new forests and reforestation.
 Geoengineering proposals that do not reduce atmospheric CO2 – for example,
methods that focus solely on temperature (such as aerosol backscatter or
reduction of greenhouse gases other than CO2) – will not prevent ocean
acidification. Adding alkaline minerals to the ocean would be effective andeconomically feasible only on a very small scale in coastal regions, and theunintended environmental consequences are largely unknown2.
 The impacts of other stressors on ocean ecosystems such as higher
temperatures and deoxygenation – also associated with increasing CO2 –will be reduced by limiting increases in CO2 levels.
 The shellfish aquaculture industry faces significant threats and may benefit
from a risk assessment and analysis of mitigation and adaptation strategies.
For example, seawater monitoring around shellfish hatcheries can identify
when to limit the intake of seawater with a lower pH, hatcheries can be
relocated, or managers can select larval stages or strains that are more
resilient to ocean acidification for breeding.
 At local levels, the effects of ocean acidification on ecosystem resilience
may be constrained by minimising other local stressors3,4,5 through thefollowing:• Developing sustainable fisheries management practices such as
regulating catches to reduce overfishing and creating long-term
bycatch reduction plans. If implemented and enforced, this type ofmanagement has been shown to sustain ecosystem resilience.
• Adopting sustainable management of habitats, increased coastal
protection, reduced sediment loading and application of marine spatialplanning.
• Establishing and maintaining Marine Protected Areas (MPAs) that
help manage endangered and highly vulnerable ecosystems to enhancetheir resilience against multiple environmental stressors6.
• Monitoring and regulating localised sources of acidification fromrunoff and pollutants such as fertilisers.
• Reducing sulphur dioxide and nitrous oxide emissions from coal-fired
power plants and ship exhausts7 that have significant acidifying effects
locally.

OCEAN ACIDIFICATION page 3

OCEAN ACIDIFICATIN

Ocean pH in 2100
High CO2 emissions scenario (RCP* 8.5)
The pH scale measures the acidity of water-based solutions.
A pH value below 7 indicates an acid; above 7
indicates an alkali. A pH decrease of one unittranslates to a 10-fold increase in acidity.
The average pH of ocean surface
waters has fallen by about 0.1
units, from 8.2 to 8.1, since
the beginning of theindustrial revolution1.
This corresponds
toa26%
increase inacidity.

ArcticArctic waters are acidifying
faster than the global
average because cold
water is richer in CO2 andmelting sea ice worsens the
problem.

CANARY
Upwelling

Benguela
Upwelling

Atmospheric CO2 and ocean pH

Observations of CO2 (parts per million) in the atmosphere and pH of
surface seawater from Mauna Loa and Hawaii Ocean Time-series (HOT)Station Aloha, Hawaii, North Pacific.
Credit: Adapted from Richard Feely (NOAA), Pieter Tans, NOAA/ESRL(www.esrl.noaa.gov/gmd/ccgg/trends) and Ralph Keeling, Scripps
Institution of Oceanography (scrippsco2.ucsd.edu)* Intergovernmental Panel on Climate Change emissions scenarios —Representative Concentration Pathways (reference 1).

Species shifts
Some species, likeseagrasses, may
thrive in more acidified
waters. Others may struggle
to adapt. Any resulting lossesof species could lead tolower biodiversity, a mark of
ecosystem health.

Observed CO2 emissions
and emissions scenarios to 2100

Global CO2 emissions (white dots, uncertainty in grey)
from fossil fuel use is following the high emissions
trajectory (red line, RCP* 8.5) predicted to lead to asignificantly warmer world. Large and sustained emissions
reductions (blue line, RCP* 2.6) are required to increase
the likelihood of remaining within the internationallyagreed policy target of 2°C.
Credit: Glen Peters and Robbie Andrew (CICERO) and
the Global Carbon Project, adapted from Peters et al.,2013 (reference 8). Historic data from Carbon Dioxide
Information Analysis Center.

Ocean acidification in numbers
increase in atmospheric carbon dioxide (CO ) levels since
40% Thethe start of the industrial revolution.
26% The increase in ocean acidity from preindustrial levels to today.
The projected increase in ocean acidity by 2100 compared with
about 170% preindustrial levels if high CO emissions continue (RCP* 8.5).
2

2

The current rate of acidification is over 10 times faster than any
time in the last 55 million years.

10 times
24 million The number of tonnes of CO the ocean absorbs every day.
2

2100

Ocean stress
Ocean acidification is one ofmany major changes happening
in the ocean. Others include
warming water, decreasing
oxygen concentration,
overfishing and eutrophication.
CALIFORNIA
Upwelling

CoralsIf high CO2 emissions
continue, changes incarbonate chemistry andwarming of the tropicalocean may hamper or
prevent coral reef growthwithin decades. Warmwater corals shown in blue.

Shellfish
Economically valuable molluscs
such as mussels and oysters
are highly sensitive to ocean
acidification. Already, someshellfisheries have had to adapt
to lower pH levels or relocate, as aresult of natural and human causes.

HUMBOLDT
Upwelling

Upwelling regions
Big changes are expectedin economically important
upwelling regions, which
already have lower natural
pH levels. Here, acidification,
warming and low oxygen
act together. (See orange
outlines.)

Ocean surface pH projections to 2100

1850

Modelled global sea-surface pH from 1870 to 2100. The
blue line reflects estimated pH change resulting from very
low CO2 emissions to the atmosphere (IPCC Representative
Concentration Pathway, RCP* 2.6). The red line reflects pHfrom high CO2 emissions (the current emissions trajectory,
RCP* 8.5).
Credit: Adapted from Bopp et al., 2013 (reference 9).
Ocean acidification maps: model projections are calculated by MPI-ESM-LR; data provided by Tatiana Ilyina from Ocean Biogeochemistry Group, Max Planck Institute for Meteorology.
Design: Félix Pharand-Deschênes, Globaïa.

OCEAN ACIDIFICATI

N

Aragonite saturation in 2100
High CO2 emissions scenario (RCP* 8.5)
ArcticParts of the Arctic are alreadycorrosive to shells of marineorganisms, and most surface
waters will be within decades.
This will affect ecosystems andpeople who depend on them.

CoralsVery high CO2 emissions will leadto unfavourable surface waterconditions for tropical coral reef
growth by 2100, according toestimates. Significant emissions
reductions could ensure 50% of
surface waters remain favourable
for coral reef growth***.

Saturation state
The “saturation state”, Omega (Ω), describes
the level of saturation of calcium carbonate inseawater. Shown here is the mineral form ofcalcium carbonate called aragonite.
If Ω is less than 1 (Ω<1), conditions are corrosive(undersaturated) for aragonite-based shells andskeletons.
When Ω>1, waters are supersaturated withrespect to calcium carbonate and conditions
are favourable for shell formation. Coral growth
benefits from Ω≥3.
By 2100, computer model projections show thatΩ will be less than 3 in surface waters aroundtropical reefs if CO2 emissions continue on thecurrent trajectory***.

Antarctic
If CO2 emissions continue on thecurrent trajectory (RCP* 8.5), 60%
of Southern Ocean surface waters(on annual average) are expected to
become corrosive to the aragoniteshelled organisms, for example
pteropods, which are part of themarine food web. Substantial
emissions reductions (RCP* 2.6)
could prevent most of the Southern
Ocean surface waters from becoming
corrosive to the shells of aragonitic
organisms**.

* Intergovernmental Panel on Climate Change emissions scenarios — Representative Concentration Pathways (reference 1).
** Personal communication: Joos & Steinacher, after Steinacher et al., 2013 (reference 10).
*** Ricke et al., 2013 (reference 11).
OCEAN ACIDIFICATION page 6

Shells and skeletons
The shells and skeletons of many marine organisms are made from either
calcite or aragonite; both are forms of calcium carbonate. Scientists are
particularly interested in aragonite, which is produced by many corals
and some molluscs, because it is more soluble than calcite.
Organisms grow shells and skeletons more easily when carbonate ions inwater are abundant – “supersaturated”. Unprotected shells and skeletonsdissolve when carbonate ions in water are scarce – “undersaturated”.

2100

Phytoplankton
The hard shells of
coccolithophores – tiny floating
marine organisms – produce alarge fraction of marine calcium
carbonate. When they die, theysink and carry carbon to thedepths of the ocean. They are
an important food source forother marine life, as well as beinga major source of the climatecooling gas dimethylsulphide(DMS).
How coccolithophores respond toocean acidification is an area ofintense investigation. While somespecies appear to be tolerant
to ocean acidification, others
show decreased calcification andgrowth rates in acidified waters.

1850

Ocean acidification maps: model projections are calculated by MPI-ESM-LR; data provided by Tatiana Ilyina from Ocean Biogeochemistry Group, Max Planck Institute for Meteorology.
Design: Félix Pharand-Deschênes, Globaïa.

OCEAN ACIDIFICATION page 7

International research coordination
 Research to decrease uncertainties is urgently needed. A coordinatedglobal network of marine experimental, observation and modelling
research is critical. Priority areas of research are responses of key species
and entire ecosystems, particularly over longer time periods; the potential
for organisms to adapt; socio-economic impacts; and the biogeochemical
feedbacks on the climate system.
 In June 2012 at the UN’s Rio+20 summit, the Ocean Acidification
International Coordination Centre was announced. The centre, basedat the International Atomic Energy Agency’s Marine Environmental
Laboratories in Monaco, will facilitate, communicate and promoteinternational activities in ocean acidification research and observation andlink science with policy.
 A Global Ocean Acidification Observing Network12 was established inJune 2012, working closely with the International Coordination Centre.
Globally, relatively few sites have multi-decadal measurements and remoteregions are poorly covered. The network will measure chemical andecosystem variables needed to provide a baseline for the timely assessmentof ocean acidification impacts. It will ensure data quality and comparability,
and it will synthesise information for societal benefit.
 Significant investment to monitor ecosystem impacts will be a key aspect of
future international research coordination activities.

Ulf Riebesell; GEOMAR Future Earth, the new 10-year international research initiative on global
sustainability, will provide a mechanism for developing an internationally
coordinated research agenda that will include issues like ocean
acidification.

Stakeholder engagement
Effective knowledge exchange among science, policy and industry sectors
is essential for effective adaptation and mitigation. A forum for dialogue
between the research community and stakeholders – the Ocean Acidificationinternational Reference User Group – has been established, building on aprevious European initiative. It will draw together a wide range of end users
and leading scientists to facilitate rapid transfer of knowledge.
In addition, Future Earth (see above) aims to provide a platform forsolutions-focused dialogue on global issues including ocean acidification.

OCEAN ACIDIFICATION page 8

Commercially and ecologicallyimportant organisms
Scientific research shows the vulnerability and sensitivity of commercially and ecologically important marine species toocean acidification at elevated levels of CO2 (adapted from Turley and Boot, 201113, and Wittmann and Pörtner, 201314).

Molluscs

Echinoderms

Clams, scallops,
mussels, oysters,
pteropods, abalone,conchs and cephalopods(squid, cuttlefish andoctopuses)

Crustaceans

FinfishCoralsSea urchins, sea
cucumbers, starfish

Shrimps, prawns, crabs,
lobsters, copepods(zooplankton), etc.

Small (herrings,
sardines, anchovies),
large (tuna, bonitos,
billfishes), demersal(flounders, halibut, cod,haddock), etc.

Warm and cold water
coral

Keystone species anda food source for fish.
Starfish are important
predators.

Zooplankton suchas copepods play acentral role in foodwebs, connecting
phytoplankton (which
they eat) to predators(fish and mammals).

Major role in thebalance of ecosystems
as top predators or inconnecting important
trophic levels.

Important ecosystemengineers, providing
habitat for a wide rangeof marine species, manyof which are specialised
to living in coral reefs.

Ecosystem role
Mussels and pteropods
are an important foodsource for fish, including
salmon (pteropods).
Mussels and oysters
provide habitats forother organisms.

Current estimated global commercial value♦$24 billion
Locally important. Direct
protein source in someisland states.

$0.7 billion
Locally important.
“Luxury” food item; sea
cucumbers are used
extensively in Chinese
traditional medicine.

$37 billion$65 billion
Significant proportionof human food, fish-oil
manufacture and fishmeal. Locally important:dependence for foodand income in someareas.

$30–375 billion◊
These hotspots ofmarine biodiversity
provide coastal
protection, attract
tourists and support
fisheries.

Few species studied.
Vulnerability in early life
stages. Some species
may become locallyextinct.

Less affected thanother groups. Thermal
tolerance of somecrabs is reduced withacidification.

Indirect effects due tochanges in prey andloss of habitats such ascorals likely. Possibly
some direct effects on
behaviour, fitness andlarval survival.

Reduced calcification,
increased bio-erosion,synergistic effectsof warming andacidification.

Vulnerability
Adults and juveniles
have shown reduced
calcification, growthand survival rates. Some
species may become
locally extinct.

Sensitivity (percent of species affected)∆
100

Species (%)

80
60
40
20
0

♦

Commercial value for fisheries represents the sum of capture fisheries and aquaculture in 2010 in US dollars15.

◊

Today’s estimated value of global goods and services provided by coral reefs, such as coastline protection,
tourism, biodiversity and food16,17.

∆

Adapted from Wittmann and Pörtner, 201314. These data are for business-as-usual trajectories of CO2 levels.

OCEAN ACIDIFICATION page 9

Images: © iStockphoto.com

GROUPSSocieties and economies
Societies depend on
the ocean for various
ecosystem services: provisioning services, suchas food; regulating services, such ascarbon absorption from theatmosphere; cultural services, such asrecreation; and supporting services, such as
nutrient cycling.
While much is known about theeffects of ocean acidification
on individual organisms,
the potential responses ofwhole ecosystems are largely
unknown. Thus, although
deleterious consequences are
expected for shellfish and warm
water corals (high confidence)and fisheries (low confidence),
it is difficult to quantify how
the ecosystems and fisheries
will change and how societies
will adapt to and manage thechanges.

Confidence levels
In this document, we use these
confidence levels (right). For
further information on how theselevels are determined, see thescientific background.

V

VERY HIGH CONFIDENCE

H

HIGH CONFIDENCE

M

MEDIUM CONFIDENCEL

LOW CONFIDENCE

V The capacity of the ocean to act as a carbon sinkdecreases as it acidifies [VERY HIGH CONFIDENCE]

The ocean provides a vast sink for anthropogenic CO2 emissions. Around
one quarter of annual CO2 emissions from human activities currently end
up in the ocean18. This service cannot be relied on in the future. Atmospheric
CO2 is rising faster than the ocean can respond. The capacity of the ocean toabsorb CO2 decreases as ocean pH decreases; that is, the buffering capacityof seawater decreases19. This reduced capacity is a concern for stabilising
CO2 emissions and implies that larger emissions cuts will be needed to meettargets to mitigate climate change.

M Declines in shellfisheries will lead to economic

losses [MEDIUM CONFIDENCE], but the extent of the losses
is uncertain

By 2100, estimated global annual economic losses due to declines in mollusc
production from ocean acidification could be more than $130 billion (US dollars,
at 2010 price levels) for a business-as-usual CO2 emissions trend, according
to one estimate20 [LOW CONFIDENCE]. For the United States, a 13% reduction
in revenue is estimated by 2060 from declines in mollusc harvests due toacidification21 [LOW CONFIDENCE]. Economically important shellfish species may
respond in different ways to ocean acidification (see table on p. 9), but we do notknow enough to make quantitative economic predictions for all fisheries yet.
Molluscs appear to be one of the most sensitive groups of organisms studied
under ocean acidification regimes. Indeed, oyster larvae in hatcheries in thenortheast Pacific Ocean region are very sensitive to ocean acidification and are
already affected by low pH waters22,23.

Social consequences
The examples illustrated here
highlight the potential for
substantial revenue declines, lossof employment and livelihoods,
and indirect economic costs that
may occur if ocean acidification
damages marine habitats, alters
marine resource availability, anddisrupts other ecosystem services.
© iStockphoto.com

OCEAN ACIDIFICATION page 10

The current estimates of economic
impacts are largely restricted tocommercially marketed ecosystemservices such as fisheries andtourism. A full assessment musttake into account ecosystem services
beyond those that are directly
market-based, such as cultural
services, regulating services (suchThresholds
M Negative socio-economic impacts of coral reef
degradation are expected [MEDIUM CONFIDENCE],
but the size of the costs is uncertain

Substantial economic losses are likely to occur due to the loss of tropical coral
reef extent from ocean acidification (by 2100, the scarcity of corals will pushthe value of their losses over $1 trillion per year, in US dollars at 2010 pricelevels, according to one estimate24) [LOW CONFIDENCE]. A large proportionof these losses will occur in vulnerable societies and small island statesthat economically rely on coral reefs. Coral reef losses will negatively affecttourism, food security, shoreline protection and biodiversity. But ocean
acidification is not the only stressor. Reefs are already under pressure fromwarmer temperatures (which cause coral bleaching), habitat destruction,
overfishing, sedimentation and pollution.
Actions that slow the rate of ocean acidification will reduce impacts andmaximise the potential for coral reefs to recover, and even adapt, to otherstressors. Thus, additional human stressors, such as destructive fishingpractices, pollution and sedimentation, will not only have immediate
ecological effects, they will also reduce the potential of coral reefs to adapt towarmer, more acidified conditions.
In addition to global climate policy, local reef management strategies– implemented using tools such as Marine Protected Areas, fisheries
management, and marine spatial planning – also increase the potential ofcoral reefs to cope with ocean acidification4,25.

L Impacts of ocean acidification on ecosystems may
affect top predators and fisheries [LOW CONFIDENCE]

It is uncertain how changes in phytoplankton and zooplankton abundanceand distribution will propagate through marine ecosystems to affect fish
and fisheries, on which many societies depend. Also, very little is known
about the direct effects of ocean acidification on fish that are the target ofcommercial and subsistence fishing, which results in high uncertainties in
predicting changes in fisheries in the future. However, this area is key for
research, as fisheries support the livelihoods of about 540 million people, or
8% of the world’s population26.

as coastal protection) and a broader
set of provisioning services (such as
marine-derived pharmaceuticals).
To a large extent, societiesthat are highly vulnerable toocean acidification are locatedin developing countries or small
island states27. Their inhabitants
rely on fish and other marine

resources as their primarysource of protein. In addition,indigenous peoples and culturesin the Arctic – where the ocean
is acidifying more rapidly thanin other locations – are also
dependent on natural resources,
and therefore these societies
are potentially vulnerable.

Can scientists define a “safe”
or “tolerable” level of ocean
acidification that must not be
exceeded?
Some decision makers are asking
scientists if it is possible to begin
defining thresholds beyond whichecosystems will not recover.
This is a complex challenge. The
combined effects of changing
ocean physics, chemistry andbiology vary from ecosystem
to ecosystem. Impacts are also
dependent on geographic locationand variable local characteristics.
Ecosystem impacts depend on
policy decisions made now inrelation to future carbon dioxide
emissions and policies relating toother marine issues. Moreover,there are complex ethical andeconomic considerations on issues
relating to “safe” or “tolerable”
levels of ocean acidification.
Science cannot answer thesequestions but can provide
some information on possible
consequences of policy options.
A dialogue between scientists,
policymakers and stakeholders
is necessary to explore whatquestions require answers andwhat options are available.
A first step towards identifying
thresholds and indicators will
be a concerted global research
effort. This should combine
experiments, models andobservations to attempt tountangle the complexity of the
response of marine ecosystems
to ocean acidification and otherstressors and will be led by the
newly established International
Coordination Centre.

OCEAN ACIDIFICATION page 11

© iStockphoto.com

OCEAN ACIDIFICATION page 12

Scientific background
Ocean acidification research is relatively new. The numbers ofscientists involved and research papers published are increasing
rapidly. New discoveries are frequent and our understanding isbeing continually refined.

Defining confidence levels
Confidence levels are expressed in this document with the qualifiers “low”,“medium”, “high” and “very high”. These qualifiers synthesise the authors’
judgments about the validity of findings as determined through evaluationof evidence and agreement. The analysis builds on statements of confidence
derived from peer-reviewed synthesis such as the European Project on
Ocean Acidification synthesis book28 and the Intergovernmental Panel on
Climate Change (IPCC) Fifth Assessment Report. The most recent metaanalyses, of 228 ocean acidification studies on marine organisms29 and 167
studies on marine animals14, provided further evidence to aid the authorsin analysing and summarising the outcomes of the experimental evidence.
Increasing levels of evidence and degrees of agreement are correlated withincreasing confidence (see figure), as outlined in the IPCC’s guidance note on
the treatment of uncertainties30 in the Fifth Assessment Report.

High agreement

High agreement

High agreement

Limited evidence

Medium evidence

Robust evidence

Agreement

Medium agreement Medium agreement Medium agreement
Limited evidence

Medium evidence

Robust evidence

Low agreement

Low agreement

Low agreement

Limited evidence

Medium evidence

Robust evidence

Evidence (type, amount, quantity, consistency)

V

VERY HIGH CONFIDENCE

H

HIGH CONFIDENCE

M MEDIUM CONFIDENCEL

LOW CONFIDENCE

Confidence scale

OCEAN ACIDIFICATION page 13

The ocean is acidifying rapidly and at an
unprecedented rate in Earth’s history
The chemistry of ocean
acidification is well understood,and scientists have wellconstrained models that can
predict changes in the surface
ocean chemistry as CO2
increases in the atmosphere.
When CO2 gas dissolves inseawater, carbonic acid isformed, changing the chemicalcomposition of the ocean:
ocean acidification.

V Ocean acidification is caused by CO2 emissions fromhuman activity to the atmosphere that end up in theocean [VERY HIGH CONFIDENCE]

The ocean currently absorbs approximately a quarter of the CO2 added to theatmosphere from human activities each year18, greatly reducing the impact of
this greenhouse gas on climate.

V Anthropogenic ocean acidification is currently inprogress and is measurable [VERY HIGH CONFIDENCE]

Anthropogenic CO2 emissions are causing chemical changes in the ocean thatare observable now and are highly predictable at a global scale into the future.
The acidity of surface ocean waters has increased about 26% since thebeginning of the industrial revolution1. With increasing dissolved CO2,
calcifying organisms will find it more difficult to build their shells.

H The ocean is acidifying more rapidly than it has inmillions of years [HIGH CONFIDENCE]

Today’s human-induced acidification is a unique event in the geologicalhistory of our planet due to its rapid rate of change.
An analysis of ocean acidification over the last 300 million years highlights
the unprecedented rate of change of the current acidification31. The mostcomparable event 55 million years ago was linked to mass extinctions ofcalcareous deep-sea organisms and significant changes to the surface ocean
ecosystem31. At that time, though the rate of change of ocean pH was rapid, it
may have been 10 times slower than current change32.

V The legacy of historical fossil fuel emissions on ocean

acidification will be felt for centuries [VERY HIGH CONFIDENCE]

The increase in atmospheric CO2 is occurring too quickly to be stabilised bynatural feedbacks such as the dissolution of deep-sea carbonates, which acts
on time-scales of thousands of years, or the weathering of terrestrial carbonate
and silicate rocks, which operates on time-scales of tens to hundreds ofthousands of years.
Global-scale projections of the changing chemistry of seawater can bemade with high accuracy from scenarios of atmospheric CO2 levels. Even if
anthropogenic CO2 emissions stopped today, the ocean’s pH would not recover
to its preindustrial level for centuries33.

OCEAN ACIDIFICATION page 14

V Reducing CO2 emissions will slow the progress ofocean acidification [VERY HIGH CONFIDENCE]

The concentration of atmospheric CO2 is approximately 395 parts per million(ppm; global average, as of 2013), which is more than 40% higher than thepreindustrial level of 280 ppm. Half of this increase has occurred in the last 33
years34. If CO2 emissions are reduced, less CO2 will enter the ocean, limiting
the extent of ocean acidification impacts33.
Reducing CO2 emissions is possible with existing or developing technology.
Currently, there are agreements to stabilise CO2 emissions to limit the global
mean temperature increase to 2°C above preindustrial levels. These levels may
still jeopardise the stability of some marine ecosystems. Current emissions aretracking a much higher global temperature increase (see box).

Future CO2 emissions: Representative Concentration Pathways
Representative Concentration
Pathways (RCPs) are future
emissions pathways used in
the Intergovernmental Panelon Climate Change’s Fifth
Assessment Report1. Many
scenarios could lead to aparticular pathway. The highest
RCP (8.5 Wm-2 radiative forcing)
represents high (business as
usual) emissions. It results inmean global warming by 2100
of about 4.3°C (likely range,
3.2°–5.4°C) above preindustrial
temperatures. The lowest RCP(2.6 Wm-2 radiative forcing)requires significant mitigation andemissions reductions resulting
in a global average temperaturerise of about 1.6°C (likely range,
0.9°–2.3°C) above preindustrial
levels.

Global marine consequences

By 2100, business-as-usual
emissions (RCP 8.5) would resultin ocean acidification leading
to the loss of 100% of tropicalsurface waters with conditions
favourable for coral reef growth.
Significant reductions (RCP 2.6)
would result in less than half of
this loss (personal communication,
Joos and Steinacher10,11).

By 2100, 60% of the Southern
Ocean surface waters (onaverage) could become corrosiveto the shells of aragonitic
organisms, a part of the marine
food chain, if emissions continue
along a business-as-usual
trajectory (RCP 8.5). With strong
mitigation (RCP 2.6), corrosive
conditions in most of theSouthern Ocean can be avoided(personal communication, Joosand Steinacher10).

Global CO2 emissions (white dots,
uncertainty in grey) from fossil fueluse are following the high emissions
trajectory (red line, RCP 8.5) predicted
to lead to a significantly warmer
world. Large and sustained emissions
reductions (blue line, RCP 2.6) are
required to increase the likelihood ofremaining within the internationallyagreed policy target of 2ºC.
Source: Glen Peters and Robbie
Andrew (CICERO) and the Global
Carbon Project, adapted fromPeters et al., 20138. Historic data from
Carbon Dioxide Information Analysis
Center.

OCEAN ACIDIFICATION page 15

How will marine organisms respond?
Most of what is known aboutorganismal responses to ocean
acidification has been obtained
from relatively short-termlaboratory experiments on single
species. Such experiments
use simplified versions of thenatural environment, but give an
indication of potential responses
in the ocean28.
In a growing number of laboratory
and field experiments multiple
organisms are studied together,for example, in gradientsof pH in naturally acidified
ecosystems and in mesocosms
with natural communities
including numerous species.
Results from a broad range ofmarine organisms show various
responses, including decreased
survival, calcification, growth,development and abundance.
There is considerable variationin the sensitivity and toleranceof marine organisms to ocean
acidification, sometimes even
within a single species. Other
organisms show a positive
response to the increased
availability of CO2. More active
organisms, such as mobile
crustaceans and fish, seemto be less sensitive to ocean
acidification. Fleshy algae,
some phytoplankton and someseagrasses may benefit from anincrease in carbon availability.
The impacts on individual species– whether they decline or benefit
from ocean acidification – maycause cascading disturbances inother parts of the food web.

OCEAN ACIDIFICATION page 16

M Anthropogenic ocean acidification will adversely

affect many calcifying organisms [MEDIUM CONFIDENCE]

Most studies demonstrate that calcification – the ability for some organisms
to produce shells or skeletons – decreases with ocean acidification29. These
include planktonic calcifiers (such as foraminifera, coccolithophorids andpteropods), corals and molluscs, as well as echinoderms (e.g., urchins) and lessso crustaceans (e.g., crabs).
An analysis of ocean acidification studies shows that many calcifying
organisms also show a decrease in survival, growth, development andabundance29. In many calcifying groups, early life stages are most sensitive toCO2-induced changes in seawater chemistry. Crustaceans are less affected thancorals, molluscs or echinoderms14.

H Molluscs (such as mussels, oysters and pteropods) are

one of the groups most sensitive to ocean acidification[HIGH CONFIDENCE]

Early life stages of many molluscs (larvae and juveniles) as well as adults haveshown reduced calcification, growth and survival. This makes molluscs one of
the groups most sensitive to ocean acidification14.

M Pteropod (marine snail) shells are already dissolving[MEDIUM CONFIDENCE]

The high-latitude oceans are already becoming corrosive to some species.
The shells of pteropods, small marine snails that are key species in the foodweb, are already dissolving in parts of the Southern Ocean, which surrounds
Antarctica35. They have special importance in the food web in polar regions,for example forming a key food source for pink salmon36.

H If CO2 emissions continue on the current trajectory,
coral reef erosion is likely to outpace reef building
sometime this century [HIGH CONFIDENCE]

Ocean acidification alone is likely to cause reef building to cease by the end of
the 21st century on the current CO2 emissions trajectory37. If coral bleaching
due to ocean warming is also taken into account, then the rates of erosion
on most reefs could outpace the overall reef building by corals and otherorganisms once CO2 levels reach 560 ppm (by mid-century under the current
emissions trajectory)38. If this happens, the degradation and loss of coral reefs
will affect whole ecosystems dependent on reefs as habitat, with consequences
for biodiversity, fisheries and coastal protection. Very aggressive reductions
in CO2 emissions are required to maintain a majority of tropical coral reefs inwaters favourable for growth11.

H Cold-water coral communities are at risk [HIGH CONFIDENCE],
and may become unsustainable

By 2100, it is estimated that 70% of cold-water corals will be exposed tocorrosive waters, although some will experience undersaturated waters as
early as 202039. Undersaturated conditions will increase the dissolution rate ofthe dead skeletons (the base of these deep-water coral communities), which
will lead to a disintegration of the cold-water coral ecosystems40,41. Their loss
would have consequences for food webs42, as they provide habitat, feeding
grounds and nursery areas for many deep-water organisms.

Ocean
cean chemistry for shell and skeleton formation
In an acidifying ocean, skeletaland shell growth generally slows
down significantly as the saturation
state decreases. For example, coral
growth benefits from high aragonite
saturation states, larger than 3(¯ ≥ 3)44.

Conditions in the deep

Deep waters naturally contain more
CO2 and have a lower pH comparedwith the surface ocean. Furthermore,calcite and aragonite saturation
decreases with increasing pressure.
The boundary between these deeper
undersaturated waters and theshallower saturated waters is known as
the “saturation horizon”.
Increasingly, the aragonite
saturation horizon is becoming
shallower and thus corrosive
conditions for shell-forming
organisms are moving
closer to the surface.

This process is well understoodand well documented at a global
scale. The saturation horizon willreach the ocean surface by the endof this century in the North Pacific,
the Arctic seas and Southern Ocean,under RCP 8.5 (see p. 15).
In upwelling areas such as in thenortheast Pacific Ocean and along
the western coasts of South Americaand Africa, naturally more acidic
deep waters upwell onto continental
shelves. The ocean uptake ofanthropogenic CO2 has increased
the extent of the areas affected bymore acidic waters45, which include
important fisheries grounds.

Christina Kellogg; USGSIn the ocean, CO2 reacts withwater and carbonate ions tocreate carbonic acid. Elevated CO2
levels reduce the concentrationof carbonate ions. Shells of many
marine organisms are made ofcalcium carbonate, which has two
main forms: calcite and aragonite.
Both minerals dissolve at low
carbonate ion concentrations– known as “undersaturated
conditions” – unless the calcifying
organisms have evolved
mechanisms to prevent dissolution,such as protective layers or othermeans to isolate their carbonate
structures from exposure tocorrosive water43. Aragonite, which
is formed by corals, by the firstlarval stages of many molluscs, andby some adult molluscs (including
pteropods), is more soluble thancalcite, which is produced bycoccolithophores, foraminifera,echinoderms and crustaceans.
The scale for describing the levelof saturation of calcium carbonate
in seawater is the “saturation state”,
Omega (¯), where ¯ < 1 indicates
undersaturated (corrosive) and¯ > 1, supersaturated waters.

OCEAN ACIDIFICATION page 17

M Ocean acidification may have some direct effects onfish physiology, behaviour and fitness [MEDIUM CONFIDENCE]

Accumulation of CO2 in animal bodies may disturb life processes, leading
to overall changes in their fitness and physiology46,47. In general, fish appear
to be less sensitive to ocean acidification than less mobile organisms. Ocean
acidification has led to a decrease in growth rates of fish larvae48.
There is some evidence that clown fish (which live in coral reefs) are altering
their behaviour (smell, hearing, visual risk, etc.), decreasing their ability
to detect predators and prey49. The long-term impacts are unclear, as thegeological record does not indicate fish are sensitive to ocean acidification, as it
does for some other organisms.
Overall, the changes in the food supply of fish are likely to have moresignificant effects on their abundance than the direct physiological effects.

H Some seagrass and phytoplankton species may
benefit from ocean acidification [HIGH CONFIDENCE]

Elevated levels of CO2 appear to stimulate photosynthesis and growth in somegroups of organisms. These include some seagrasses, fleshy algae and some
phytoplankton groups (e.g., cyanobacteria and picoeukaryotes)50. Observationsin ocean areas with naturally high CO2 venting (e.g., the island of Ischia, Italy)
show that marine plants prosper in the acidified waters51.

H The combination of ocean acidification and increased
temperatures negatively affects many organisms[HIGH CONFIDENCE]
Ocean acidification appears to narrow the thermal tolerance of someorganisms56, and others are more vulnerable to ocean acidification in warmer
waters. The response to both changes together is often larger than the
response to those changes taken separately52. Studies show a trend towards
lower survival, growth and development when elevated temperatures andocean acidification occur together. The combination of ocean acidification andwarming may result in shifts in species diversity and ecosystem compositionby the reduction of habitat range.

Jason Hall-Spencer

OCEAN ACIDIFICATION page 18

Warm-water corals are also susceptible to bleaching during periods ofunusual warmth. Several mass coral bleaching events have occurred since
1979, resulting in warm-water coral mortality worldwide53. Tropical coral reefs
are particularly at threat from the combined effects of warming and ocean
acidification.

How will marine ecosystems respond?
H The varied responses of species to ocean

acidification and other stressors are likely to lead tochanges in marine ecosystems [HIGH CONFIDENCE], but theextent of the impact is difficult to predict

We know that some organisms, such as seagrasses and some phytoplankton,
seem to thrive under acidified conditions, while others, such as corals andshellfish, are harmed. These sensitivities – combined with other related
stressors such as global warming – are likely to lead to changes in species
composition, thus changing food sources for predators. There are many
uncertainties in our ability to predict these changes and their consequences,
but there is high agreement among scientists that changes are likely to besignificant54.
Knowledge gaps that have to be filled are as follows: What will replace
species that disappear? Will the role in the ecosystem of the replacement
species be the same? What will be the consequences for ecosystems? How will
this affect the biogeochemical cycles on which life depends? Will some species
be able to adapt in time? (See adaptation box.) Are there carry-over effects fromgeneration to generation?

Despite rapid advances inocean acidification research,
we are still unable to makereliable projections of the
impacts on marine ecosystems
and fisheries. How wholeecosystems respond to ocean
acidification is thus a priority
area of research. Laboratory
studies and single-organism
studies cannot simply be
extrapolated to the wholeecosystem. However, there
is enough evidence to allow
scientists to draw somepreliminary conclusions withvarious levels of confidence.

Adaptation
Acclimation is the ability of an individual organism to adjust toenvironmental change. Acclimation can occur at various time-scales within
the lifetime of the organism. The responses, which are generally reversible,
allow the organism to perform across a range of environmental conditions.
Adaptation is the evolutionary response of a population – over multiple
generations – to a modified environment. The potential for evolutionary
adaptation is highest in species with short generation times and large
population sizes.

Short-term experimental studies of a species’ response to environmental
change do not generally account for adaptive processes. The observed
responses may therefore overestimate the long-term sensitivity of natural
populations to environmental change. However, mass extinctions seenin the geological record, in time periods when the rate of ocean change
was much slower than it is today, suggest that evolutionary rates ofsome species may not be fast enough for them to adapt to the multiple
environmental changes projected for the future ocean [HIGH CONFIDENCE].

Photo by NEON ja; coloured by Richard Bartz

There is experimental evidence for evolutionary adaptation to ocean
acidification in some short-lived microorganisms, including calcareous
microalgae (coccolithophores)55. Members of this group have a high genetic
diversity, short generation times of a day or less, and huge population sizesof up to a million cells per litre of seawater. In contrast, organisms withlonger generation times, such as corals, may struggle to adapt with themagnitude and rate of ocean acidification that will occur in this century.

OCEAN ACIDIFICATION page 19

H Multiple stressors compound the effects of ocean
acidification [HIGH CONFIDENCE]

The problems organisms face with ocean acidification are often compoundedby other stressors, such as rising temperature56, loss of oxygen (deoxygenation),
ocean stratification9,57, overexploitation, pollution, extreme events, increasing
UV-B irradiance (due to stratospheric ozone depletion)58 and changes
in salinity. Some of these stressors are also caused by excess CO2 in theatmosphere.
At a global level, increased stratification causes decreased productivity at
low latitudes – towards the equator – where nutrients are limited. Additionally,large parts of the low-latitude ocean are vulnerable to deoxygenationas temperatures rise. The combined impact of ocean acidification anddeoxygenation could result in far-reaching consequences on ocean
biogeochemistry, such as the creation of large “dead zones” and increased
marine denitrification and anaerobic ammonium oxidation, affecting themarine nitrogen cycle9,57. Changes in the deep ocean as a result of ocean
acidification are poorly studied.

L Ocean acidification will alter biogeochemical cycles at
a global scale [LOW CONFIDENCE]

Changing ecosystem composition and the oceans’ carbonate chemistry affects
biogeochemical cycles in complex ways. Some organisms will thrive under
ocean acidification and others will struggle. The changes to phytoplankton
and zooplankton will in turn affect predators that rely on these organisms
for food. Ocean acidification may also affect production of nitrous oxide, apotent greenhouse gas, and DMS, a climate-cooling compound. We need tounderstand ecosystem responses to the effects of ocean acidification on thecycling of key nutrients, in order to improve how global models simulate andpredict biogeochemical changes59.

M Nitrogen fixation in some cyanobacteria may be

stimulated by ocean acidification [MEDIUM CONFIDENCE]

NASA’s Goddard Space Flight Center/USGSOCEAN ACIDIFICATION page 20

There is some evidence that nitrogen fixation in some cyanobacteria will be
stimulated by ocean acidification54. This process converts nitrogen gas to abiologically available form, providing a major input of nutrients into the ocean.
This could have consequences for the nitrogen cycle and the productivity ofthe oceans, as large parts of the ocean are nitrogen-limited.

References
1. IPCC, 2013. Working Group I Contribution
to the IPCC Fifth Assessment Report,
Climate Change 2013: The Physical Science
Basis, Summary for Policymakers, www.
climatechange2013.org/images/uploads/
WGIAR5-SPM_Approved27Sep2013.pdf
2. The Royal Society, 2005. Ocean
Acidification Due to Increasing Atmospheric
Carbon Dioxide. The Royal Society, London.
3. Billé, R., Kelly, R., Biastoch, A., HarrouldKolieb, E., Herr, D., Joos, F., Kroeker,
K., Laffoley, D., Oschlies, A., Gattuso,
J.-P., 2013. Taking action against ocean
acidification: a review of management andpolicy options. Environmental Management
52:761–779, doi:10.1007/s00267-013-0132-7.
4. Pandolfi, J.M., Connolly, S.R., Marshall,
D.J., Cohen, A.L., 2011. Projecting coral reef
futures under global warming and ocean
acidification. Science 333(6041):418–422,
doi:10.1126/science.1204794.
5. Rau, G.H., McLeod, E.L., Hoegh-Guldberg,O., 2012. The need for new ocean
conservation strategies in a high-carbon
dioxide world. Nature Climate Change
2:720–724, doi:10.1038/nclimate1555.
6. US National Research Council, 2001.
Marine Protected Areas: Tools for Sustaining
Ocean Ecosystem. The National Academies
Press, Washington, D.C.
7. Hassellöv, I.-M., Turner, D.R., Lauer, A.,
Corbett, J.J., 2013. Shipping contributes toocean acidification. Geophysical Research
Letters 40:2731–2736, doi:10.1002/grl.50521.
8. Peters, G.P., Andrew, R.M., Boden, T.,
Canadell, J.G., Ciais, P., Le Quéré, C.,
Marland, G., Raupach, M.R., Wilson,
C., 2013. The challenge to keep global
warming below 2 °C. Nature Climate
Change 3:4–6, doi:10.1038/nclimate1783.
9. Bopp, L., Resplandy, L., Orr, J.C., Doney,
S.C., Dunne, J.P., Gehlen, M., Halloran,
P., Heinze, C., Ilyina, T., Seferian, R.,
Tjiputra, J., Vichi, M., 2013. Multiple
stressors of ocean ecosystems in the 21st
century: projections with CMIP5 models.
Biogeosciences 10:6225–6245.
10. Steinacher, M., Joos, F., Stocker, T.F., 2013.
Allowable carbon emissions loweredby multiple climate targets. Nature
499(7457):197–201, doi:10.1038/nature12269.
11. Ricke, K.L., Orr, J.C., Schneider, K.,
Caldeira, K., 2013. Risks to coral reefs
from ocean carbonate chemistry changes
in recent earth system model projections.
Environmental Research Letters 8:034003,
doi:10.1088/1748-9326/8/3/034003.

12. www.pmel.noaa.gov/co2/story/Internatio
nal+OA+Observing+Network
13. Turley, C., Boot, K., 2011. The ocean
acidification challenges facing science andsociety. In Gattuso, J.-P., Hansson, L. (eds.),
Ocean Acidification. Oxford University
Press, 326 pp.
14. Wittmann, A.C., Pörtner, H.-O., 2013.
Sensitivities of extant animal taxa toocean acidification. Nature Climate Change
doi:10.1038/nclimate1982.
15. FAO, 2012. Fisheries and Aquaculture
Statistics 2010. Food and Agriculture
Organization of the United Nations,Rome.
16. Cesar, H.J.S., Burke, L., Pet-Soede, L.,2003. The Economics of Worldwide Coral
Reef Degradation. Cesar Environmental
Economics Consulting, Arnhem,and WWF-Netherlands, Zeist, The
Netherlands. 23 pp. Online at: http://
assets.panda. org/downloads/
cesardegradationreport100203.pdf.
17. Costanza, R., d’Arge, R., de Groot, R.,
Farber, S., Grasso, M., Hannon, B.,
Limburg, K., Naeem, S., O’Neil, R.V.,
Paruelo, J., Raskin, R.G., Sutton, P., vanden Belt, M., 1997. The value of the world’s
ecosystem services and natural capital.
Nature 387:253–260.
18. Le Quéré, C., Raupach, M.R., Canadell,J.G., Marland, G., Bopp, L., Ciais, P.,
Conway, T.J., Doney, S.C., Feely, R.A.,
Foster, P., Friedlingstein, P., Gurney, K.,
Houghton, R.A., House, J.I., Huntingford,
C., Levy, P.E., Lomas, M.R., Majkut,J., Metzl, N., Ometto, J.P., Peters, G.P.,
Prentice, I.C., Randerson, J.T., Running,
S.W., Sarmiento, J.L., Schuster, U., Sitch,
S., Takahashi, T., Viovy, N., van der Werf,
G.R., Woodward, F.I., 2009. Trends inthe sources and sinks of carbon dioxide.
Nature Geoscience 2:831–836, doi:10.1038/
ngeo689.
19. Sabine, C.L., Feely, R.A., Gruber, N., Key,
R.M., Lee, K., Bullister, J.L., Wanninkhof,
R., Wong, C.S., Wallace, D.W.R., Tilbrook,
B., Millero, F.J., Peng, T.-H., Kozyr, A., Ono,
T., Rios, A.F., 2004. The oceanic sink foranthropogenic CO2. Science 305(5682):367–
371, doi:10.1126/science.1097403.

21. Cooley, S.R., Doney, S.C., 2009.
Anticipating ocean acidification’s
economic consequences for commercial
fisheries. Environmental Resource Letters
4:024007, doi:10.1088/1748-9326/4/2/024007.
22. Barton, A., Hales, B., Waldbusser, G.G.,
Langdon, C., Feely, R.A., 2012. The Pacificoyster, Crassostrea gigas, shows negative
correlation to naturally elevated carbon
dioxide levels: Implications for near-term
ocean acidification effects. Limnology andOceanography 57(3):698–710, doi:10.4319/
lo.2012.57.3.0698.
23. Waldbusser, G.G., Brunner, E.L., Haley,
B.A., Hales, B., Langdon, C.J., Prahl, F.G.,
2013. A developmental and energetic
basis linking larval oyster shell formationto acidification sensitivity. GeophysicalResearch Letters 40:2171–2176, doi:10.1002/
grl.50449.
24. Brander, L.M., Rehdanz, K., Tol, R.S.J.,
Van Beukering, P.J.H., 2012. The
economic impact of ocean acidificationon coral reefs. Climate Change
Economics 3(1):1250002, doi:10.1142/
S2010007812500029.
25. Ateweberhan, M., Feary, D.A.,
Keshavmurthy, S., Chen, A.,
Schleyer, M.H., Sheppard, C.R., 2013.
Climate change impacts on coral
reefs: Synergies with local effects,
possibilities for acclimation, andmanagement implications. Marine
Pollution Bulletin 74:526–539, doi:10.1016/j.
marpolbul.2013.06.011.
26. FAO, 2010. State of World Fisheries andAquaculture, 2010. FAO Fisheries andAquaculture Department, Food andAgriculture Organization of the United
Nations, Rome.
27. Cooley, S.R., Lucey, N., Kite-Powell, H.,
Doney, S.C., 2012. Nutrition and income
from molluscs today imply vulnerability
to ocean acidification tomorrow. Fish andFisheries 13:182–215, doi:10.1111/j.14672979.2011.00424.x.

20. Narita, D., Rehdanz, R., Tol, R.S.J., 2012.
Economic costs of ocean acidification: alook into the impacts on global shellfish
production. Climatic Change 113:1049–1063,
doi: 10.1007/s10584-011-0383-3.

OCEAN ACIDIFICATION page 21

28. Gattuso, J.-P., Hansson, L. (eds.), 2011.
Ocean Acidification. Oxford University
Press, 326 pp.
29. Kroeker, K.J., Kordas, R.L., Crim, R.,
Hendriks, I.E., Ramajo, L., Singh,
G.S., Duarte, C.M., Gattuso, J.-P., 2013.
Impacts of ocean acidification on marineorganisms: quantifying sensitivities andinteraction with warming. Global Change
Biology 19:1884–1896, doi: 10.1111/gcb.12179.
30. Mastrandrea, M.D., Field, C.B., Stocker,
T.F., Edenhofer, O., Ebi, K.L., Frame,
D.J., Held, H., Kriegler, E., Mach, K.J.,
Matschoss, P.R., Plattner, G.-K., Yohe, G.W.,
Zwiers, F.W., 2010. Guidance Note for Lead
Authors of the IPCC Fifth Assessment Reporton Consistent Treatment of Uncertainties.
Intergovernmental Panel on Climate
Change (IPCC). Available at www.ipcc.ch.
31. Hönisch, B., Ridgwell, A., Schmidt, D.N.,
Thomas, E., Gibbs, S.J., Sluijs, A., Zeebe, R.,
Martindale, R.C., Greene, S.E., Kiessling,W., Ries, J., Zachos, J.C., Royer, D.L., Barker,
S., Marchitto Jr., T.M., Moyer, R., Pelejero,C., Ziveri, P., Foster, G.L., Williams, B.,
2012. The geological record of ocean
acidification. Science 335(6072):1058–1063,
doi:10.1126/science.1208277.
32. Ridgwell, A., Schmidt, D.N., 2010. Past
constraints on the vulnerability of marine
calcifiers to massive carbon dioxide
release. Nature Geoscience 3:196–200,
doi:10.1038/ngeo755.
33. Joos, F., Frölicher, T.L., Steinacher, M.,
Plattner, G.-K., 2011. Impact of climatechange on ocean acidification projections.
In Gattuso, J.-P., Hansson, L. (eds.), Ocean
Acidification. Oxford University Press,
326 pp.
34. GLOBALVIEW-CO2: Cooperative
Atmospheric Data Integration Project Carbon Dioxide. NOAA ESRL, Boulder,
Colorado [Available at www.esrl.noaa.gov/
gmd/ccgg/globalview/], 2012.
35. Bednarsek, N., Tarling, G.A., Bakker,
D.C.E., Fielding, S., Jones, E.M.,
Venables, H.J., Ward, P., Kuzirian, A.,
Leze, B., Feely, R.A., Murphy, E.J., 2012.
Extensive dissolution of live pteropods
in the Southern Ocean. Nature Geoscience5(12):881–885, doi:10.1038/ngeo1635.
36. Armstrong, J.L., Boldt, J.L., Cross,
A.D., Moss, J.H., Davis, N.D., Myers,
K.W., Walker, R.V., Beauchamp, D.A.,
Haldorson, L.J., 2005. Distribution, size,
and interannual, seasonal and diel food
habits of northern Gulf of Alaska juvenile
pink salmon, Oncorhynchus gorbuscha.
Deep-Sea Research (Part II, Topical Studies in
Oceanography) 52:247–265.

OCEAN ACIDIFICATION page 22

37. Fabricius, K.E., Langdon, C., Uthicke, S.,
Humphrey, C., Noonan, S., De’ath, G.,
Okazaki, R., Muehllehner, N., Glas, M.S.,
Lough, J.M., 2011. Losers and winners
in coral reefs acclimatized to elevatedcarbon dioxide concentrations. Nature
Climate Change 1(3):165–169, doi:10.1038/
nclimate1122.
38. Silverman, J., Lazar, B., Cao, L., Caldeira,K., Erez, J., 2009. Coral reefs may startdissolving when atmospheric CO2
doubles. Geophysical Research Letters
36:L05606, doi:10.1029/2008GL036282.
39. Guinotte, J.M., Orr, J., Cairns, S., Freiwald,A., Morgan, L., George R., 2006. Will
human-induced changes in seawaterchemistry alter the distribution of
deep-sea scleractinian corals? Frontiers in
Ecology and the Environment 4:141–146.
40. Form, A., Riebesell, U., 2012. Acclimation
to ocean acidification during long-term
CO2 exposure in the cold-water coral
Lophelia pertusa. Global Change Biology
18:843–853.
41. Lunden, J., Georgian, S.E., Cordes,
E.E., 2013. Aragonite saturation states
at coldwater coral reefs structured by
Lophelia pertusa in the northern Gulf
of Mexico. Limnology and Oceanography
58(1):354–362.

49. Munday, P.L., Dixsona, D.L., Donelson,
J.M., Jones, G.P., Pratchett, M.S.,
Devitsina, G.V., Døving, K.B., 2009.
Ocean acidification impairs olfactory
discrimination and homing ability of amarine fish. Proceedings of the National
Academy of Sciences 106(6):1848–1852.
50. Riebesell, U., Tortell, P.D., 2011. Effects ofocean acidification on pelagic organisms
and ecosystems. In Gattuso, J.-P., Hansson,
L. (eds.), Ocean Acidification. Oxford
University Press, pp. 99–121.
51. Hall-Spencer, J.M., Rodolfo-Metalpa, R.,
Martin, S., Ransome, E., Fine, M., Turner,
S.M., Rowley, S.J., Tedesco, D., Buia, M.-C.,
2008. Volcanic carbon dioxide vents show
ecosystem effects of ocean acidification.
Nature 454:96–99.
52. Harvey, B.P., Gwynn-Jones, D., Moore,
P.J., 2013. Meta-analysis reveals complex
marine biological responses to theinteractive effects of ocean acidification
and warming. Ecology and Evolution
3:1016–1030.
53. Hoegh-Guldberg, O., 1999: Climatechange, coral bleaching and the futureof the world’s coral reefs. Marine andFreshwater Research 50:839–866.

42. Roberts, J.M., Wheeler, A.J., Freiwald, A.,
2006. Reefs of the deep: The biology andgeology of cold-water coral ecosystems.
Science 213:543–547.

54. Gattuso, J.-P., Bijma, J., Gehlen, M.,
Riebesell, U., Turley, C., 2011. Ocean
acidification: knowns, unknowns andperspectives. In Gattuso, J.-P., Hansson,
L. (eds.), Ocean Acidification. Oxford
University Press, 326 pp.

43. McCulloch, M., Falter, J., Trotter, J.,
Montagna, P., 2012. Coral resilience toocean acidification and global warming
through pH up-regulation. Nature Climate
Change 2:623–627, doi:10.1038/nclimate1473.

55. Lohbeck, K.T., Riebesell, U., Reusch,
T.B.H., 2012. Adaptive evolution of a
key phytoplankton species to ocean
acidification. Nature Geoscience 5:346–351,
doi:10.1038/NGEO1441.aa.

44. Kleypas, J.A., McManus, J.W., Meñez,
L.A.B., 1999. Environmental limits to coral
reef development: where do we draw theline? American Zoologist 39(1):146-159.

56. Pörtner, H.O., Farrell, A.P., 2008.
Physiology and climate change. Science
322:690–692.

45. Feely, R.A., Sabine, C.L., Hernandez-Ayon,
J.M., Ianson, D., Hales, B., 2008. Evidence
for upwelling of corrosive “acidified”
water onto the Continental Shelf.
Science 320(5882):1490–1492, doi:10.1126/
science.1155676.
46. Fabry, V.J., Seibel, B.A., Feely, R.A., Orr,
J.C., 2008. Impacts of ocean acidification
on marine fauna and ecosystem processes.
ICES Journal of Marine Science 65:414–432.
47. Pörtner, H.-O., 2012. Integrating climaterelated stressor effects on marineorganisms: unifying principles linking
molecule to ecosystem-level changes.
Marine Ecology Progress Series 470:273–290.
48. Baumann, H., Talmage, S.C., Gobler, C.J.,
2012. Reduced early life growth andsurvival in a fish in direct response toincreased carbon dioxide. Nature Climate
Change 2(1):38–41.

57. Gruber, N., 2011. Warming up,
turning sour, losing breath: ocean
biogeochemistry under global change.
Philosophical Transactions of the Royal
Society A 369(1943):1980–1996, doi:10.1098/
rsta.2011.0003.
58. Gao, K., Helbling, E.W., Häder, D.-P.,
Hutchins, D.A., 2012. Response of marine
primary producers to interactions
between ocean acidification, solar
radiation and warming. Marine Ecology
Progress Series 470:167–189, doi:10.3354/
meps10043.
59. Riebesell, U., Gattuso, J.-P., Thingstad,
T.F., Middelburg, J.J., 2013. Arctic ocean
acidification: pelagic ecosystem andbiogeochemical responses during amesocosm study. Biogeosciences 10:5619–
5626.

We gratefully acknowledge the following organisations fortheir financial and in-kind support for the symposium.
US National Science Foundation
Prince Albert II of Monaco Foundation
Monterey Bay Aquarium Research InstituteMonterey Bay Aquarium
Monterey Bay Sanctuary Foundation
Naval Postgraduate School
International Union for Conservation of Nature
World Commission on Protected Areas
COMPASSUK Ocean Acidification Research Programme
Gordon and Betty Moore Foundation
US National Oceanic and Atmospheric Administration
US National Marine Sanctuaries
Blue Ocean Film Festival
GoogleX-Prize
Ulf Riebesell; GEOMAR

Symposium sponsors

Scientific Committee
on Oceanic ResearchIntergovernmental
Oceanographic
Commission of UNESCO

International GeosphereBiosphere ProgrammeThis extended version of the summary for policymakers
is available from www.ocean-acidification.net
and sponsor organisation websites.
For more information,email: comms@igbp.kva.se
Or telephone:+46 8 16 64 48

We acknowledge financial support by KIOST(Korea Institute for Ocean Science and Technology)
to print this Summary for Policymakers.
This document was produced with the financial assistance of the Prince Albert II of Monaco Foundation.
The contents of this document are the sole responsibility of IGBP, SCOR and IOC and can under nocircumstances be regarded as reflecting the position of the Prince Albert II of Monaco Foundation.