Download climate change: changing oceans

climate change
climate change: changing oceans
ICES (the International Council for the Exploration of the Sea),
coordinates, and promotes marine research in the North Atlantic
Ocean and adjacent seas, e.g. the Baltic Sea. ICES acts as a focal point
for a community of more than 1600 marine scientists from 20 Member
Countries. Besides filling gaps in the knowledge of marine ecosystems,
marine research is also developed into unbiased, non-political advice.
This advice is then used by the Member Countries to help them manage
human activities in the North Atlantic Ocean and adjacent seas.
H.C Andersens Boulevard 44–46
DK-1553 Copenhagen V
Denmark
telephone
+45 33 38 67 00
telefax
+45 33 93 42 15
email
[email protected]
website
www.ices.dk
ICES plans and coordinates marine research through a system of
committees, more than 100 working groups, science symposia, and an
Annual Science Conference. Research on climate change and variability
has been part of ICES work since it was established more than one
hundred years ago, but during the past two decades, there has been
a growing awareness of the importance of climate change among the
marine science community. This brochure provides a state-of-the-art
overview of ICES studies on climate change and variability.
There is great confidence within the scientific community that climate
change is a reality. Global atmospheric concentrations of the“greenhouse”
gases – carbon dioxide (CO2), methane, and nitrous oxide – have
increased as a result of fossil fuel use and changing systems of agriculture.
The increase in these gases has caused warming of the atmosphere and
ocean, rising sea levels, and changing wind patterns. As greenhouse-gas
emissions continue to rise, so will the global temperature, leading to
further melting of ice and rises in sea level.
Evidence of a changing climate from the IPCC
In the last 100 years, the average global temperature has increased by 0.74˚C. This temperature increase is widespread over the
globe and is greater at higher northern latitudes. However, temperature anomalies may be patchy and vary regionally.
Eleven of the 12 years from 1995 to 2006 rank among the 12 warmest years in the instrumental records of global surface
temperature, which began in 1850.
Global average sea level has risen since 1961 at an average rate of 1.8 mm year−1 and, since 1993, the rate has nearly doubled
to 3.1 mm year−1, as a result of thermal expansion and melting glaciers, ice caps, and polar ice sheets.
Observed decreases in snow and ice extent are also consistent with warming: satellite data since 1978 reveal that annual
average Arctic sea-ice extent has shrunk by 2.7% per decade.
According to the International Panel on Climate
Change (IPCC), atmospheric concentrations of
greenhouse gases have increased markedly since
1750, as a result of human activities, and now exceed
pre-industrial values, as measured from ice cores
spanning thousands of years. As a result of the
greenhouse effect, average global temperatures have
increased by ~0.6°C, and 11 of the 12 years from
1995 to 2006 rank among the 12 warmest years in the
instrumental records, which date from 1850. Over the
last century, as temperatures have increased, sea level
has risen by 0.17 m, and the IPCC has predicted that
sea level will have risen by a further 0.2–0.6 m by 2100
(Figure 1).
The sea is also predicted to become more acidic
over the next few centuries as a consequence of the
increasing level of CO2 in the ocean. One of the most
important implications of the changing acidity of
the oceans is the problems that it may cause for the
many marine photosynthetic organisms and animals,
e.g. corals, bivalves, and some plankton species that
make their shells and plates out of calcium carbonate
(CaCO3). The process of “calcification”, which for
some marine organisms is important to their biology
and survival, will be reduced as the water becomes
acidic (less alkaline). From the evidence available,
there is much uncertainty as to whether marine
species, communities, and ecosystems will be able to
acclimate or evolve in response to changes in ocean
chemistry. At this stage, research into the impacts of
high concentrations of CO2 in the oceans is still in
its infancy.
Another major concern is that the circulation system
of the Atlantic Ocean may change. The Atlantic
thermohaline circulation is the process by which
warm water moves northwards at the surface of
the Atlantic Ocean and cold, deep water moves
southwards. This process is driven by differences in
water temperature and salinity, and any variations
introduced by climate change (e.g. greater freshwater input from higher rainfall and melting ice) are
likely to have an impact. The thermohaline circulation
is unlikely to shut down, but some models predict a
reduction of the overturning circulation as a result of
climate change by 30%.
On a more regional scale, altered atmospheric
conditions may bring changes in storm tracks,
winds, rainfall, evaporation, sea ice, and river run-off.
Changing weather systems will affect ocean currents,
ocean fronts, and upwelling and downwelling, which,
in turn, will profoundly affect the distribution and
production of marine ecosystems at all levels, from
plankton to fish.
In addition to potentially altering the distribution
of productive areas, changing weather patterns are
also predicted to increase the formation of vertically
stratified water. Stratification is a natural process that
occurs, for example, when the sun heats up the sea
surface, creating a layer of warm water above the
layers of much colder water below; this may also
occur when river water enters the sea and forms
layers of low density over the denser seawater. The
major problem with stratification is that it restricts
access to nutrients, which become “locked” into the
stratified layers. This means, for example, that the
nutrients in the surface waters are gradually used up
by phytoplankton, but are not replenished from the
depths. More nutrients are only released when the
stratified water is mixed by wind action, and the more
stratified the water, the more wind energy is needed
to break it up. In the North Sea, for example, the
duration of a stable seasonal stratification is predicted
to increase as a result of climate change, because
higher rainfall will increase fresh-water inputs, via
rivers and the Baltic Sea, into the eastern North Sea.
However, stronger winds will contribute to increased
vertical mixing in the upper water layer.
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The marine climate of Europe is predicted to
continue to warm throughout the 21st century,
with a forecasted rise in sea surface temperature
of 0.2°C per decade. It is thought that warmer
sea temperatures have already caused significant
changes in zooplankton and phytoplankton
populations, including changes in their abundance
and distribution. In 2006, the ICES Working Group
on Zooplankton Ecology (WGZE) reported that, in
the North Sea in particular, the population of the
previously dominant zooplankton species (the cold-
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the trend in the north atlantic in the past
decade (1997-2007) has been of warming and
increasing salinity in the upper ocean.
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A changing ocean climate has led to a biogeographical
shift in certain crustacean plankton assemblages in
European shelf seas over the past 40 years. This socalled “regime shift”, first detected by British and
French scientists in the late 1990s, was reflected by
a northward extension of warm-water species and a
decrease in the numbers of colder water species. In
2005, this regime shift was confirmed for the North
Sea by the ICES Regional Ecosystem Study Group for
the North Sea (REGNS), which used a large variety of
biological and other parameters.
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Figure 2: Overview of upper ocean temperature anomalies in 2007 from the long-term average
across the North Atlantic. Dark red areas indicate warmer than average water. From ICES Report
on Ocean Climate 2007.
climate change is affecting
not only the food that fish
eat but also the distribution
of fish.
The study of a 70-year time-series of fish, plankton,
and intertidal animals in the English Channel revealed
that warm-water species increased in large numbers
during warm periods. The warm-water species moved
up to 67 km northwards in order to take advantage
of “new” habitat, then moved southwards during
cooler periods. Another study, on the distribution
of 20 fish species in the North Sea in the period
1977–2001, found that half of them demonstrated
northward shifts coinciding with recent warmer
conditions. One of the species most affected was the
bib or pouting (Trisopterus luscus), which increased
its northern range by more than 300 km. Analysis
of Scottish trawl data, taken from research vessels
and dating back to 1926, also found that catches of
warm-water species, i.e. anchovy (E. encrasicolus),
sardine (Sardina pilchardus), and striped red mullet
(Mullus surmuletus), all increased in the North Sea,
coinciding with increased temperatures after 1995. It
is noteworthy that a similar extension of anchovy and
sardine was observed in the 1950s.
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Coping with climate change
Climate change is affecting not only the food that
fish eat but also the distribution of fish. Fish are
known to seek out their preferred temperature range.
Therefore, if the sea temperature increases, fish at the
northern limit of their temperature range will have
new, more northerly areas to move into as formerly
cold water becomes more habitable. In contrast, fish
at the southern limit of their range will be forced to
move northwards to escape the rising temperatures.
Evidence shows that this is already happening.
Alternatively, apparent shifts in distribution may be
the result of more successful recruitment in the few
individuals living at the edge of their temperature
preferences. For example, the increased abundance
of anchovy (Engraulis encrasicolus) in the southern
North Sea is caused by recruitment in this area rather
than movement from more southerly waters.
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Figure 1: Observed changes in (a) global average surface
temperature; (b) global average sea level from tidal gauge (blue)
and satellite (red) data and (c) Northern Hemisphere snow cover
for March-April. All differences are relative to corresponding
averages for the period 1961-1990. Smoothed curves represent
decadal averaged values while circles show yearly values.
The shaded areas are the uncertainty intervals estimated from
a comprehensive analysis of known uncertainties (a and b) and
from the time series (c). Source: IPCC 4th Assessment Report
(AR 4, 2007)
water crustacean Calanus finmarchicus) had decreased
in biomass by 70% between the 1960s and the post1990s. Warm-water species had moved northwards to
replace C. finmarchicus, but their biomass was not as
high. Farther south, other warm-water zooplankton
species, e.g. the crustacean Temora stylifera (Figure 4),
have been recorded moving northwards through the
Bay of Biscay. In some regions, changes in plankton
biomass and seasonal timing of blooms have already
been linked to the poor recruitment of young fish to
several stocks of commercial interest and to the low
breeding success of seabirds in recent years. This is
because the life cycles of many fish and seabirds are
timed to make optimum use of peaks of particular
prey species; if the timings are “out of sync”, because
of changes in the plankton blooms, less food will be
available for both fish and seabirds.
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Changes in temperature, sea level and Northern
Hemisphere snow cover
Figure 3. The trend in the North Atlantic in the past decade (1997–2007) has been one of
warming and of increasing salinity in the upper ocean. Warming is shown in a time-series of
temperature from 2150 stations in the central Greenland Sea for the period 1950–2007. Blue
indicates cold water, and green, yellow, and red indicate warm water. Source: ICES Data Centre.
Other research has highlighted the northward
movement of warm-water fish, e.g. the silvery john
dory (Zenopsis conchifera) and rosy dory (Cyttopsis
rosea), through Portuguese waters up to the southwest
coast of Ireland, since the 1960s.
The changing distribution of the striped red mullet in
the North Sea is shown in Figure 5. The small panels
show the distributions in the periods 1977–1989
(top left) and 2000–2005 (top right). The main panel
shows the changes in distribution between the two
periods. A change from blue to green indicates an
increase in density between the two periods, with
dark green to blue indicating the largest changes.
Yellow to red indicates a decrease in density, with red
indicating the largest changes. The graph (top centre)
shows the proportion of the total survey area where
an increase and decrease occurred, broken down by
the degree of increase or decrease (1–6). In the period
1983–1986, striped red mullet were rarely found by
research vessels. By early 2001–2004, they were found
as far north as Scotland.
Figure 4. Abundance of the warm-water copepod Temora
stylifera in transects off Vigo, Coruña, and Santander, and other
plankton surveys along the North Spanish coast. This crustacean
was absent before 1978 but has been recorded in increasing
quantities since the mid-1990s.
cod stocks at the colder extremes
such as those off eastern canada,
greenland, and in the barents
sea would benefit from increased
recruitment and faster growth as
the sea warmed.
During the 1920s and 1930s, the warming of the
air and ocean temperatures in the northern North
Atlantic and the high Arctic led to reduced ice cover
in the Arctic and Subarctic regions and to higher sea
temperatures. Atlantic cod (Gadus morhua) and halibut
(Hippoglossus hippoglossus) expanded northwards
along the west coast of Greenland in response to the
changes in the ocean climate. Other species were also
observed to have undergone significant abundance
and distributional changes. For example, cold-water
species such as the beluga whale (Delphinapterus
leucas) no longer migrated as far south in winter as
in previous cold years. This was a clear case of an
environmentally driven ecosystem response that
became of paramount interest for fishery researchers
at the time. This interest lead to the first scientific
meeting by ICES on climate change held in 1948
at Copenhagen entitled “Climate Changes in the
Arctic in Relation to Plants and Animals”. This was
followed up by a new meeting in 1952 on “Fisheries
Hydrography”.
In the invitation to the first meeting, the conveners wrote, “Thus it is
clear that some of the largest fisheries in the northern hemisphere,
e.g. some cod fisheries, during the coming years will be completely
dependent on the course of the present mild period in the northern
waters”. This document shows that the ICES science community was
concerned about the climate change impacts on the marine ecosystem
for a very long time.
Since 1992, the ICES/GLOBEC (Global Ocean Ecosystems Dynamics)
“Cod and Climate Change” programme has focused on cod. This has
yielded some key results on cod biology and ecology that have helped
scientists to estimate the future impact of warmer temperatures. The
results are a mixture of good and bad news. Climate models estimate
that, by 2100, the temperature will increase by 2°C in most areas
occupied by cod. Cod stocks are not found in waters with annual mean
bottom temperatures greater than 12°C. It has been estimated that, if
there is a sustained rise in sea temperature of just 1°C, several of the
southern cod stocks will become stressed; for example, stocks in the
Celtic Sea and English Channel will eventually disappear, while stocks
in the Irish Sea, the southern North Sea, and Georges Bank will decline
owing to decreasing recruitment. On the other hand, cod stocks at the
colder extremes, e.g. those off eastern Canada, Greenland, and in the
Barents Sea, will benefit from increased recruitment and faster growth
as temperature increases.
Temora stylifera, a planktonic crustacean species floating freely
in the water column. Drawing by Giesbrecht, 1892.
What Is Climate Change and Climate Variability?
Any change in climate over time either is caused by natural variability or is a result of human activity. Following
the IPCC, global climate change refers to changes caused by the accumulation of greenhouse gases in the
lower atmosphere. The global concentration of these gases is increasing, caused mainly by human activities.
In general, global climate change includes those changes that are attributed directly or indirectly to human
activity through altering the composition of the global atmosphere and ocean, and that are in addition to
natural climate variability over comparable time periods. The term climate variability is used when referring to
variations not related to anthropogenic influences. Climate variability occurs over different time-scales such
as seasonal, annual, decadal, and multidecadal and is caused by differences in solar input, volcanic eruptions,
internal dynamics of the atmosphere, etc. These natural variations may act to either oppose or enhance those
changes due to global climate change, e.g. they may impede or accelerate the warming due to anthropogenic
effects.
Climate change – a greater impact in semi-enclosed seas?
Baltic Sea – predictions suggest decreases in salinity ranging from 8% to
50% and an increase in sea surface temperature of 2–4°C.
North Sea – predictions for salinity vary, from an expected increase in
some areas to an expected decrease in others. Sea surface temperature
is predicted to rise by about 1.6–3.0°C in the northern North Sea and by
3.0–3.9°C in the shallower southern North Sea.
Striped red mullet (Mullus surmuletus).
Courtesy of Robert A. Patzner, Salzburg University.
On the seabed, life generally moves at a slower
pace, but the effects of climate change and warmer
temperatures may also be felt there. The ICES Study
Group on the North Sea Benthos Project (NSPB
2000) compared records of marine animals living in
the sediment at the turn of the 20th century with
records from a similar survey in 1986. As with work
on fish species, it is difficult to separate the effects
of climate change on distribution and abundance
from the effects of fishing – e.g. bottom trawling –
but the NSPB did note that some species appear to
be responding to increased sea surface temperatures,
e.g. the brittlestar Acrocnida brachiata, which occurred
more frequently in the eastern North Sea, especially
in German Bight and on the Dogger Bank, in the
year 2000 than it did in 1986. The ICES Benthos
Ecology Working Group (BEWG) has also reported
on a general increase of warm-water species in the
southern North Sea, e.g. the amphipod crustacean
Megaluropus agilis on the Dogger Bank, whereas coldtemperate species, e.g. the polychaete worm Ophelia
borealis, have decreased in abundance.
Keeping an eye on climate change
Although the implications of climate change may
appear to be a fairly recent discovery, the potential
for humans to alter the world’s climate was foreseen
over a century ago (in 1896) by the Swedish scientist
Svante Arrhenius, who worked out that the burning of
fossil fuels could cause a greenhouse effect that would
warm up the climate. He made a series of simple
calculations which showed that the temperature in
the Arctic regions would rise by about 8–9°C if the
CO2 level were to increase to two or three times its
value at the start of the 20th century. His predictions
turned out to be correct, and now scientists all over
the world are trying to follow changes in the climate
and predict their future impacts.
In the North Atlantic Ocean, scientists working
through ICES are trying to understand the probable
future for marine ecosystems. ICES is the oldest
marine science organization in the world and, for
more than a century, has been coordinating and
promoting marine research with the help of scientists
from its 20 Member Countries. ICES acts as a catalyst,
bringing scientists together from all avenues of marine
research and helping them to pool their knowledge
and data, and then disseminate their findings. Rather
than working on a national scale, ICES gives scientists
a forum through which they can work on the larger,
international picture.
Figure 5. The change in distribution of striped red mullet
(Mullus surmuletus) between the periods 1977–1989 and
2000–2005 in the first quarter (Q1) of the North Sea. (See text
for explanation.)
The following is a small sample of the key groups in
the ICES community whose work has been focused
on understanding the impacts of climate change on
marine ecosystems.
ICES/GLOBEC Working Group on Cod and Climate Change
Role: The WGCCC has worked for over a decade running cooperative workshops
and theme sessions, and undertaking comparative studies – to bring researchers together
and to develop a better understanding of the cod and how it is likely to react to climate
change.
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Output: ICES Symposium Volume 198, entitled “Cod and Climate Change” (ICES
Symposium, 23–27 August 1993, Reykjavik), later in 2008 the publication of a book which
draws together the current state of knowledge of cod and its response to climate change,
newsletters, many papers, as well as ICES Cooperative Research Report No. 274 entitled
“Spawning and Life History Information for North Atlantic Cod Stocks”
(http://www.ices.dk/pubs/crr/crr274/crr274.pdf).
Weblink: http://www.ices.dk/iceswork/wgdetail.asp?wg=WGCCC
ICES Working Group on Zooplankton Ecology
Role: The WGZE provides expertise on zooplankton in the ICES area and focuses on monitoring the impacts of climate change
on plankton communities.
Output: ICES Zooplankton Status Report, issued since 1999. These reports give a North Atlantic scale and visual overview
of zooplankton distributions for the preceding years (in the form of time-series), with a brief interpretation of the ecological
significance of the results.
Weblink: http://www.ices.dk/iceswork/wgdetail.asp?wg=WGZE
ICES Working Group on Oceanic Hydrography
Role: The WGOH provides expertise on physical oceanography, particularly on climate and variability in the ICES region. It also
stimulates ICES involvement in international climate-monitoring programmes.
Output: ICES Report on Ocean Climate (formerly ICES Annual Ocean Climate Status Summary), issued annually since 1998. These
reports draw together oceanographic data from Member Countries into summary ocean “weather” reports (http://www.ices.dk/
marineworld/oceanclimate.asp).
Weblink: http://www.ices.dk/iceswork/wgdetail.asp?wg=WGOH
ICES/IOC Steering Group on the Global Oceanic Observing System
Role: The SGGOOS helps to organize the ICES contribution to the further development and implementation of GOOS in the
North Atlantic Ocean. The aim is to merge ICES existing monitoring studies into a global network of standardized observations on
climate and its effect on marine ecosystems. One aspect of ICES role in GOOS is the North Sea Pilot Project (NORSEPP), whose
aim is to promote the use of operational oceanography for biological applications, e.g. fish-stock assessments.
Output: NORSEPP currently produces quarterly reports on oceanography and fish stocks in the North Sea (www.ices.dk/
marineworld/norsepp.asp).
Weblink: http://www.ices.dk/iceswork/wgdetail.asp?wg=SGGOOS and http://www.ices.dk/iceswork/wgdetail.asp?wg=PGNSP
Closing the gaps
Although a lot of research has already been completed
on climate change by scientists within ICES, and
around the world, there is still a huge amount of
work to be done. It is important not only to continue
with the existing time-series but also to initiate
new research in key areas where more efforts are
needed into the impacts of climate change on marine
ecosystems. These key areas are highlighted below.
ICES Working Group on Operational Oceanographic Products
Role: The aims of the WGOOP, which is currently being set up, is to translate oceanographic data into the most useful format for
scientists working on other aspects of the marine ecosystem, e.g. fishery scientists.
Output: forecast – near-real-time status reports.
ICES/GLOBEC Working Group on Life Cycle and Ecology of Small Pelagic Fish
Role: The WGLESP will have an increased focus on the responses of fish to climate change, with the aim of helping fishery
scientists and other scientists working on aspects of the marine ecosystem.
Other recent work includes a workshop looking into the significance of changes of surface CO2 and ocean pH in ICES shelf sea
ecosystems as an upcoming issue.
The work of ICES working groups is used to deliver advice now on climate change issues. For example, ICES examined the
evidence for, and advised on the implications of, the effect of climate change on the distribution and abundance of marine species
in the OSPAR Maritime Area linked to changes in sea surface temperature.
Priceless data
ICES maintains a huge bank of oceanographic data for its Member Countries, with records dating from the
early 1900s. These data are now crucial because they allow scientists to monitor changes in the sea as a result of
climate change; they also provide a guide as to what is normal variability and what is out of the ordinary range.
Oceanographic data are now collected from a huge network of sampling stations and transects in all four
corners of the North Atlantic Ocean This is organized by ICES Member Countries and makes the region one of
the best monitored in the world. One of the key uses of these data is to create the flagship annual ICES Report
on Ocean Climate.
Another key data store is the records of fish and shellfish catches since 1903 and a database of trawling survey
records (DATRAS) for the last 35 years, both of which help scientists to follow changes in fish communities as
a result of climate change.
Improvement of circulation models
• Current global circulation models, driven by
climate scenarios, need to become more focused so
that they are more relevant at the regional scale. In
addition, more research is needed into the impact of
climate change on the behaviour of the thermohaline
circulation. Special emphasis also needs to be placed
on research into semi-enclosed areas, because these
are the areas that will be greatly affected by climatedriven changes.
Effects of climate change on marine life
• Further research is needed into the impact of
climate change on marine species (e.g. fish, benthic
animals) in the presence of non-climatic stressors,
e.g. fishing. There is also a need for more studies
on the impact of climate change at population and
community levels, because direct climatic effects on
individuals do not translate directly into changes in
distribution and abundance of the population as a
whole.
• More information is needed about the evolution
of fish in the marine environment and their genetic
adaptability to climate change. Furthermore, a better
understanding of the links between plankton and
larval fish in relation to future warming scenarios is
crucial. Likewise, more research into the movement
of species into European waters will lead to a
better understanding of their impact on marine
ecosystems.
Ocean acidification: a subtle but worrying
change
• Research is needed into the impacts of ocean
acidification on marine species and their physiology,
particularly cold-water corals, cephalopods, bivalves,
and echinoderms, and especially fish larvae. Process
studies, experimental work, and field studies should
be integrated into biogeochemical, circulation, and
climate models for the evaluation of the future
impacts of ocean acidification.
Managing marine ecosystems in a changing
climate
• Research is needed into the sustainable exploitation
and appropriate management of fish stocks – including
recovery strategies – in order to give fish the best
chance of adapting to environmental changes. The
ecosystem approach to fishery management requires
an insight into the infrastructure of fish stocks and
how they function. This requires detailed information
about the ecology of important marine species.
• Monitoring and evaluation of areas suitable for
spatial closure as Marine Protected Areas (MPAs) is
needed. In particular, MPA proposals will need to
take into account the potential impacts of climate
change on the distribution of target species.
• Further development of advanced ecosystem
models and multidisciplinary research is needed to
improve the detection, prediction, and forecasting of the
response of the marine ecosystem to climate change.