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EN CLIME
Climate Change
in the Baltic Sea
2021 Fact Sheet
baltic.earth
Climate change BSEP n°180
EMBARGOED
For preview purposes only. Do not share.
helcom.fi baltic.earthClimate Change in the Baltic Sea Fact Sheet 2021
In memory of Christian Dieterich Introduction
EMBARGOED
For preview purposes only.
Published by: Do not share. Contents
Helsinki Commission – HELCOM
Katajanokanlaituri 6 B
00160 Helsinki, Finland
www.helcom.fi
This document is part of the flagship publication series of HELCOM, the Baltic Sea Environment Proceedings (BSEP) The Baltic: A sea of change 6 Indirect parameters: Ecosystem 36
that have been running since the entry into force of the first Helsinki Convention in 1980. Although this document has Baltic Sea Expert Network on Climate Change – EN CLIME 7 Oxygen 38
been approved for publication by the members of the Helsinki Commission, views expressed in this publication are Impact map 7 Microbial community and processes 39
the authors’ own and might vary from those of the Helsinki Commission or its members. Any maps that are featured Confidence assessment 7 Benthic habitats 40
in this publication are intended for illustration purposes only and do not necessarily designate the exact boundaries of Parameters covered 8 Coastal and migratory fish 41
sovereign states and entities. Peer review of key messages 8 Pelagic and demersal fish 42
Climate change & climate mitigation 8 Waterbirds 43
The development of this publication was steered by the Joint H
ELCOM/Baltic Earth Expert Network on Climate Change Connections between parameters 9 Marine mammals 44
(EN CLIME). Climate future of the Baltic Sea 10 Non-indigenous species 45
Projections under a medium climate scenario 10 Marine protected areas 46
For bibliographic purposes this document should be cited as: Nutrient concentrations and eutrophication 47
“Climate Change in the Baltic Sea. 2021 Fact Sheet. Baltic Sea Environment Proceedings n°180. H
ELCOM/Baltic Earth 2021.” Direct parameters (overview) 12 Ecosystem function 48
Indirect parameters: Ecosystem (overview) 14
© 2021 Baltic Marine Environment Protection Commission Indirect parameters: Human use (overview) 16 Indirect parameters: Human use 50
(Helsinki Commission – H
ELCOM) Offshore wind farms 52
Direct parameters 18 Coastal protection 53
All rights reserved. Information included in this publication or extracts thereof, with the exception of images and graphic Air temperature 20 Shipping 54
elements that are not H ELCOM's or Baltic Earth's own and identified as such, may be reproduced without prior consent Water temperature 21 Tourism 55
on the condition that the complete reference of the publication is given as stated above. Large scale atmospheric circulation 22 Fisheries 56
Sea ice 23 Aquaculture 57
Contributors: Solar radiation 24 Blue Carbon storage capacity 58
Markus Ahola, Lena Bergström, Mats Blomqvist, Dieter Boedeker, Florian Börgel, Ida Carlén, Thomas Carlund, Jacob Salinity and saltwater inflows 25 Marine and coastal ecosystem services 59
Carstensen, Jesper Philip Aagaard Christensen, Martyn Futter, Elie Gaget, Matthias Gröger, Volker Dierschke, Christian Stratification 26
Dieterich, Morten Frederiksen, Anders Galatius, Bo Gustafsson, Claudia Frauen, Jannica Haldin, Antti Halkka, Christina Precipitation 27
Halling, Jürgen Holfort, Kari Hyytiäinen, Klaus Jürgens, Mart Jüssi, Laura Kaikkonen, Meri Kallasvuo, Markus Kankainen, River run-off 28
Martin Karlsson, Dorte Krause-Jensen, Anders Kiessling, Erik Kjellström, Antanas Kontautas, Karol Kuliński, Sanna Carbonate chemistry 29
Kuningas, Jukka Käyhkö, Petra Kääriä, Janika Laht, Ari Laine, Gesine Lange Antti Lappalainen, Terhi Laurila, Maiju Riverine nutrient loads and atmospheric deposition 30
Lehtiniemi, Knut-Olof Lerche, Urmas Lips, Georg Martin, Michelle McCrackin, H.E. Markus Meier, Noora Mustamäki, Bärbel Sea level 31
Müller-Karulis, Rahmat Naddafi, Lauri Niskanen, Antonia Nyström Sandman, Jens Olsson, Diego Pavón-Jordán, Jonas Wind 32 Glossary 62
Pålsson, Mika Rantanen, Artūras Razinkovas-Baziukas, Berit Recklebe, Gregor Rehder, Jan H. Reißman, Martin Reutgård, Waves 33 Policy linkages 65
Stuart Ross, Marta Ruiz, Anna Rutgersson, Jarkko Saarinen, Lauri Saks, Oleg Savchuk, Mikhail Sofiev, Katarzyna Spich, Sediment transportation 34 References 66
Jani Särkkä, Markku Viitasalo, Jouni Vilma, Joonas Virtasalo, Isa Wallin, Ralf Weisse, Johan Wikner, Wenyan Zhang,
Eduardo Zorita, Örjan Östman
Acknowledgements:
Maris Arro, Paweł Banaś, Imre Banyasz, Edyta Białowąs, Penina Blankett, Matthias Brenner,Laura Briekmane, Michele Casini,
Johan Dannewitz, Michael Dähne, Jacques Delsalle, Rune Dietz, Łukasz Dziemian, Anthony David Fox, Oksana Glibko,
Magnus Huss, Norbert Häubner, Birgit Hünicke, Tamara Jadczyszyn, Eglė Jakubavičiūtė, Dominika Juszkowska, Magdalena
Kamińska, Agnes Karlsson, Marcin Kawka, Ilga Kokorite, Harri Kuosa, Joakim Lagner, Kristina Lehnert, Adam Lejk, Peter
Löwe, Katarina Magnusson, Sofia Malmsten, Piotr Margoński, Johanna Mattila, Iwona Pawliczka, Liisa Pietola, Maris Plikss,
Inese Pommere-Bramane, Konrad Prandecki, Marcus Reckermann, Daria Ryabchuk, Hanna Sjölund, Piotr Skowron, Miriam
Sollich, Henrik Svedäng, Agata Święcka, Morten Tange, Maciej Tomczak, Lasse Tor, Emma Undeman, Jacek Walczak,
Tamara, Zalewska, Sergey Zhuravlev, Marek Zieliński
We also thank the four anonymous and independent reviewers for their detailed and constructive comments that
considerably helped to improve the fact sheet.
Further acknowledgements go to the FutureMARES EU project (https://www.futuremares.eu/)
Editors: Jannica Haldin, Petra Kääriä, H.E. Markus Meier, Jonas Pålsson
Layout: Dominik Littfass
ISSN: 0357-2994
3Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Introduction Introduction
Climate change effects on the
Baltic Sea environment are manifold. It is for example
expected that water temperature and sea level will rise,
and sea ice cover will decrease. This will affect ecosys-
tems and biota; for example, range shifts are expected
for a number of marine species, benthic productivity
will decrease, and breeding success of ringed seals will
be reduced. The impacts will hence affect the overall
ecosystem function and also extend to human uses of
the sea; trawling will follow the fish towards southern
areas, aquaculture will likely face a shift towards spe-
cies diversification, and the value of most ecosystem
services is expected to change — to name a few.
This Climate Change Fact Sheet provides the latest
scientific knowledge on how climate change is cur-
rently affecting the Baltic Sea and how it is expected to
develop in the foreseeable future. It is aimed at guiding
policy makers to take climate change into account, but
also to the general public. Updated Baltic Sea Climate
Change Fact Sheets are expected to be published
approximately every seven years.
4 5Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Introduction Introduction
also important information on the other param-
Baltic Sea Expert Network on Climate
The Baltic:
eters, there was a need to reduce the total 34 pa-
Change - EN CLIME rameters to the presented parameters to make
the map more legible. The presented parameters
A sea of change In 2018, the Baltic Sea Environment Protection
Commission (HELCOM) and Baltic Earth formed
a joint Expert Network on Climate Change in
have 1) direct societal relevance/experience and/
or relevance for other parameters, 2) medium to
high confidence of the changes relative to the
the Baltic Sea region (EN CLIME). This Expert noise and model/expert judgement uncertain-
Introduction Net-work involves more than 110 scientists ty under the RCP4.5 scenario, and 3) a hotspot
from around the Baltic Sea. The purpose of the sub-region in the Baltic with medium to high
network is to function as a coordinating frame- confidence of patterns of the regional changes.
work and a platform to harness the expertise
of leading scientists on both direct and indirect
Climate change impacts are evident This Fact Sheet provides the latest scientific effects of climate change on the Baltic Sea envi-
in the Baltic Sea: water temperature knowledge on how climate change is affect- ronment and ecosystems and make this exper- Confidence assessment
is rising, ice extent is decreasing, and ing the Baltic Sea in a concise format. It is the tise available to and open up for closer dialogue
annual mean precipitation is increasing over the first of a series of successive Baltic Sea Climate with policy makers. The level of confidence of statements is shown
northern part of the region. All these changes Change Fact Sheets aiming to track advances in with confidence assessments using the scale
affect the nature of the sea, its ecosystems, and the understanding of how climate change im- low-medium-high (Figure 1). The authors were
ecosystem services, as well as the human activ- pacts the state of marine systems, drawing on asked to consider both the level of consensus
ities depending on the sea. For example, many the best available science for the region. Impact map and the amount of evidence when defining an
wintering birds have shifted their wintering range How climate change already has and is ex- overall confidence of a statement and to select
northwards, the numbers of warm water fish pected to impact the Baltic Sea is described The impact map (pages 10-11) depicts projected the overall confidence by using the precaution-
species (such as sticklebacks) are increasing, the through 34 parameters that have been iden- regional changes for some of the most relevant ary principle (e.g., in case the level of consensus
risk of infection of human-pathogenic Vibrio spp. tified by EN CLIME as being of relevance for parameters in a particular subbasin of the Baltic is low and the amount of evidence medium, the
has increased through surface water warming, science and management. These parameters Sea under the RCP4.5 scenario. While there is overall confidence is low).
and trawl fishing now begins earlier in the year. constitute physiochemical parameters that are
The Baltic Sea is facing a complex system of ef- directly affected by climate change, referred to
fects and feedbacks between climatic and non-cli- as direct parameters (page 18), as well as eco-
matic factors. Multiple environmental pressures system and human use parameters that are
affect the ecosystem, and climate change adds indirectly affected, referred to as indirect pa-
further cumulative pressures to the existing an- rameters (page 36). The full list of parameters is Overall
thropogenic ones. These various climate change shown in Table 1 (page 8). Confidence assessment confidence
effects are not straightforward to understand and The first part of this report provides summary
are difficult to distinguish from certain human information of climate change impacts on each
pressures. Climate and other human-induced parameter (pages 12-17), as well as an impact
high
pressures vary significantly between different map showing the projected regional changes High agreement High agreement High agreement High
regions in the Baltic Sea, making it impossible to for a selected suite of parameters under the Limited evidence Medium evidence Robust evidence confidence
Agreement, consensus
find simple management solutions that can work RCP4.5 climate scenario across the Baltic Sea.
everywhere. In order to mitigate these negative The second part of the report (pages 18-59)
medium
effects, policymakers need to be aware of these gives a more detailed, yet concise, overview of
differences and utilise an adaptive management climate change impacts on each parameter - de- Medium agreement Medium agreement Medium agreement Medium
approach based on the best available science. scribed as key messages. Limited evidence Medium evidence Robust evidence confidence
low
Low agreement Low agreement Low agreement Low
Limited evidence Medium evidence Robust evidence confidence
low medium robust
Evidence (type, amount, quality, consistency)
Not available/
applicable
Figure 1. The overall confidence is resulting from the confidence assessment of the agreement/consensus on and
evidence of the assessed data.
6 7Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Introduction Introduction
Parameters covered Peer review of key messages Connections between parameters Categories
The 34 parameters have been categorized into six The key messages have been peer reviewed and Links between the different parameters have Energy cycle
different categories: Energy cycle, Water cycle, Car- improved in a two-step process. The first review been shown in Figure 2, depicting complex in- Water cycle
bon and Nutrient cycles, Sea level and wind, Biota round was carried out by six external scientists terconnections between the different abiotic, Carbon and nutrient cycle
and ecosystems, Human activities, and Services. and the second round was carried out by the Co- ecosystem, and human dimension parameters. Sea level and wind
The following parameters were considered as chairs and HELCOM Secretariat. The colour of each arrow comes from the pa- Biota and ecosystems
important to include, but due to the lack of lead rameter it originates from. Human activities
authors, they were not included in this version of Services
the fact sheet: Climate change & climate mitigation
Marine a services
ecosyste
re
Air temperature
n
mperatu
latio
circu
— Pelagic habitats (incl. phytoplankton and The global climate is changing, and this is due to
stor
nd coas
m
Water te
zooplankton community structure, spring human influence in the form of greenhouse gas
Blue apacity
atm e-scale
age
eric
blooms, functional traits etc.) emissions (GHG) from fossil fuel use and land
osph
c
carb
tal
Larg
— Harmful algal blooms (HABs) use change. The current changes in the climate
Aqu
on
acu
— Pollution and hazardous substances systems have already had widespread impacts
ice
ltu
din tion
Sea
— Ecotoxicology on human and natural systems.
s
re
es
lou ia
d c rad
— Human health According to the Intergovernmental Panel on
Fis
an lar
he
— Pathogens Climate Change (IPCC)1, human activities are es-
So
rie
s
s
timated to have caused approximately 1.1°C of nd ow
Tou ty a r infl
global warming above pre-industrial levels and ris
i
lin te
m Sa ltwa
Table 1. Full list of EN CLIME parameters. The asterisk (*) indicates those global warming will continue during the coming sa
parameters that include information on extreme events. decades. The pace and magnitude of warm- and
ation tion
ing will depend on how global greenhouse gas Ship tific ula
Direct parameters Categorization emissions evolve.
pin
g Stra an circ
oce
Air temperature* Energy cycle In order to reduce the impacts of rising tem-
Water temperature* Energy cycle perature on Earth, all global policy actions Coast
al pro n
Large scale atmospheric circulation Energy cycle aiming at the mitigation of greenhouse gas tectio itatio
n Precip
Sea ice* Energy cycle emissions are highly relevant. With the help of
Solar radiation Energy cycle climate models and various emission scenarios,
Salinity and saltwater inflows* Water cycle projections of global and regional climates have
Offshore wind fa
Stratification Water cycle been performed to support policymaking such rms River run-off
Precipitation* Water cycle as the Paris Agreement.
River run-off* Water cycle Different Representative Concentration Path-
Carbonate chemistry Carbon and nutrient cycles ways (RCPs) are used to describe different cli-
tion Carbonate chem
Riverine nutrient loads and atmospheric deposition Carbon and nutrient cycles mate futures depending on the greenhouse Ecosystem func istry
Sea level* Sea level and wind gas emissions in the coming years. The RCPs
Wind* Sea level and wind indicate a possible range of radiative forcing
(difference between solar energy absorbed by ns River
Waves* Sea level and wind ntratio in
and a e nutrien
the Earth and radiated back to space) in the year nt conce hication tmos t
Sediment transportation* Sea level and wind rie
Nut d eutro p ph. d loads
2100. The RCPs include a “mitigation” scenario an ep.
which aims to keep global warming below 2°C
Indirect parameters Categorization above pre-industrial temperatures (RCP2.6) and cted Oxy
prote reas gen
Oxygen Carbon and nutrient cycles a high emissions “worst case” scenario (RCP8.5), ine a
Mar
Microbial community and processes Biota and ecosystems that corresponds to a future without climate
Benthic habitats mitigation. One intermediate scenario is the us Se
Biota and ecosystems no s al
dige ecie ev
el
Coastal and migratory fish Biota and ecosystems RCP4.5 which is used in the impact map of this in sp
n-
Pelagic and demersal fish Biota and ecosystems Fact Sheet and likely results in global mean tem- No
perature rise between 2-3°C by 2100.
Wi
ls
Waterbirds Biota and ecosystems
ma
nd
am
Marine mammals Biota and ecosystems When the IPCC Assessments have been re-
em
ferred to in this Climate Change Fact Sheet, the
Wa
Non-indigenous species
ds
Biota and ecosystems
rin
bir
ves
Ma
Marine protected areas (MPAs) Biota and ecosystems information is based on the IPCC Assessment Re-
ter
Sedi sportati
d
tran
l fish
dem lagic an
Wa
Nutrient concentrations and eutrophication Biota and ecosystems port 5 (2013)2, the Special Report on the Ocean
migrato l and
Microbia ssess
men
ry fish
and pro
and Cryosphere in Changing Climate (2019)3
Benthic habitats
ersa
Ecosystem function Biota and ecosystems
t
Coasta
Pe
Offshore wind farms Human activities
and earlier publications, as the most recent As-
ce
l commu
on
Coastal protection
sessment Report 6 had not yet been published
Human activities
by the time this Fact Sheet was produced. Infor-
Shipping Human activities
mation about regional climate change is based
nity
Tourism Human activities
upon the BACC Reports (BALTEX and Baltic Earth
Fisheries Human activities
Assessments of Climate Change for the Bal-
Aquaculture Human activities tic Sea Basin, BACC Author Team, 20084; BACC Figure 2. Linkages between the different parameters that were used in the assessment of
Blue carbon storage capacity Services II Author Team, 20155; see www.baltic.earth). the effects of climate change in the Baltic Sea.
Marine and coastal ecosystem services Services
8 9Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Introduction Introduction
Bothnian Bay
Air temperature is projected to rise, most
pronounced in the northern Baltic Sea
region during winter. Sea surface tem-
perature would rise and sea ice thickness
and the length of the ice season would Gulf of Finland
decrease. Winter precipitation including Sea surface temperature would rise
Climate future of high-intensity extremes would increase.
Increased freshwater discharge would
and sea ice cover, ice thickness and the
length of the ice season would decrease,
affecting ringed seal breeding and prob-
the Baltic Sea
bring more dissolved organic carbon to
the sea, affecting benthic habitats by 1 ably causing a decline of the populations
decreasing pelagic primary production in the eastern Gulf of Finland. Likewise
and phytoplankton sedimentation. Land breeding and wintering areas of migra-
is rising faster than the projected sea tory water birds would be affected. Wave
level and the mean sea level would sink heights would increase and the potential
Projections under a medium Bothnian Sea relative to land. for shipping would increase if the ice
climate scenario (such as RCP4.5) Sea surface temperature would rise cover is reduced, but shipping intensity
is more dependent on market develop-
everywhere in the Baltic and in all
seasons. Most pronounced would be ment than climate change. In the eastern
The impact map depicts projected regional Gulf of Finland, mean sea level would
changes for some of the most relevant summer warming in the Bothnian Bay
and Bothnian Sea. Winter precipitation rise relative to the land, and higher storm
parameters in a particular subbasin of the surges would occur.
Baltic Sea under the RCP4.5 scenario. While including high-intensity extremes would
there is also important information on the increase. Increased freshwater discharge
would bring more dissolved organic car-
other parameters, there was a need to reduce
bon to the sea, affecting benthic habitats
2
the total 34 parameters to the presented
parameters to make the map more legible. by decreasing pelagic primary produc-
The presented parameters have 1) direct tion and phytoplankton sedimentation.
societal relevance/experience and/or relevance In the Bothnian Sea, Gulf of Finland and
for other parameters, 2) medium to high Gulf of Riga, the decline in sea ice cover
confidence of the changes relative to the noise would be largest. Waves would be higher Baltic Proper
and model/expert judgement uncertainty and shipping might increase if the ice Sea surface temperature would rise. If 3
under the RCP4.5 scenario, and 3) a hotspot cover is reduced. Food accessibility for BSAP measures on nutrient loads were to
sub-region in the Baltic with medium to high migratory water birds would improve be implemented, phosphorus concentra-
confidence of patterns of the regional changes. causing a northward shift of breeding tions and algal blooms would decrease
and wintering areas towards ice free and oxygen conditions of the deep water
coastal areas. In the Archipelago Sea, would improve. Without load reductions,
ringed seal populations might decrease. only minor changes in nutrient concentra-
tions are expected. The combined effects
of warming and planned nutrient reduc-
tions will eventually lead to less carbon
reaching the seafloor, reducing benthic
animal biomass. In shallow archipelago
waters, the fates of benthic animal and 4
plant populations depend on local vari-
ations in biogeochemistry and primary
productivity. In the southern Baltic, mean 5
sea level would rise relative to the land,
and higher storm surges would occur. Gulf of Riga
Sediment transports would change. Sea surface temperature would rise and
sea ice cover would decline, affecting
ringed seal populations in the northern
Baltic Sea entrance area Gulf of Riga. Likewise, breeding and
Sea surface temperature would rise. Mean wintering areas of migratory water birds
sea level is projected to rise relative to 6 would be affected. In the southern Gulf
the land, and higher storm surges would of Riga, mean sea level would rise rela-
occur. Higher atmospheric pCO2 would tive to the land, and higher storm surges
cause increased acidification. would occur.
Assessment sub-basins
1. Bothnian Bay (Bothnian Bay and the Quark)
2. Bothnian Sea (Bothnian Sea and Åland Sea)
3. Gulf of Finland
4. Gulf of Riga
5. Baltic Proper (Northern Baltic Proper, Western
Gotland Basin, Eastern Gotland Basin,
Bornholm basin and Gdansk Basin)
6. Entrance area (Kattegat, Great Belt, the Sound,
Kiel Bay, Bay of Mecklenburg and Arkona
Basin)
10 11Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Direct parameters Direct parameters
Categories
Energy cycle
Direct parameters Water cycle
Carbon and nutrient cycle
Sea level and wind
Physiochemical parameters directly affected by climate change Biota and ecosystems
Human activities
Services
Air temperature Water temperature Large scale atmospheric Sea ice Solar radiation Salinity and saltwater Stratification Precipitation
Air temperature shows the The marginal seas around the circulation Sea ice forms every winter, The solar radiation is the inflows Seawater is layered (stratified) Precipitation depends on
clearest response to in- globe have become warmer The climate of the Baltic the most important factor engine of the climate Salinity affects the dynamics of according to its density, the circulation, the amount
creased greenhouse gas emis- during the past 40 years. The Sea region is strongly being air temperature, but also system. The solar radiation ocean currents and ecosystem a property governed by of water vapor in the air, the
sions. A significant air tem- sea surface temperature of influenced by the large-scale wind, snow cover and ocean reaching the surface strongly functioning. Salinity decreases temperature and salinity. Over temperature and the land-
perature increase in the Baltic the Baltic Sea has warmed atmospheric circulation, in currents. Over the past 100 depends on cloudiness, and gradually from Kattegat to the the last 40 years, stratification sea contrast. Annual mean
Sea region has been observed more than the average for particular the North Atlantic years, the winters have become also on aerosols. There is Bothnian Bay. Inflows from in the Baltic Sea has become precipitation has significantly
during the last century, larger the global ocean and will Oscillation, atmospheric milder, the ice season shorter an indication of decline in the North Sea sporadically stronger. This trend may increased over the northern
than the global trend, and continue to warm. blocking patterns, and and the maximum ice extent cloudiness during the past renew the deep water with continue in the future and Baltic Sea lately while in the
this increase is expected to Atlantic Multidecadal decreased. This development decades. For the future, there saline, oxygen rich water. No cause harm to the marine south, changes are small – a
continue. In addition, warm Oscillation are dominant is expected to continue in a is very limited knowledge. statistically significant trends in ecosystem by decreasing the trend that may continue in
extremes are projected to patterns. As the response of changing climate. salinity have been found, and mixing between surface waters the future.
become more pronounced. these atmospheric circulation uncertainties of future projec- and deep waters.
patterns to climate change tions are high.
differs among models, future
projections are very uncertain.
River run-off Carbonate chemistry Riverine nutrient loads Sea level Wind Waves Sediment transportation
Runoff describes the amount The carbonate system regu- and atmospheric deposition Baltic Sea mean level The wind climate and storms The wave climate in the Near shore sediment transport
flowing water entering the lates seawater pH. The amount External nutrient inputs from responds to global sea level over the Baltic Sea are Baltic Sea strongly depends is triggered by waves and
sea. The total annual river of CO2 in the Baltic Sea surface land and atmosphere are the rise and regional land uplift determined by the large-scale on the wind field and shows wind and leads to erosion and
runoff has not changed water changes seasonally major long-term drivers of the and varies with season and atmospheric circulation. large long-term variability. accumulation of sediments.
over the last 500 years, but mostly due to biologically Baltic Sea eutrophication. Sub- climate. Baltic sea level is Storms are typically more Significant trends in the wave Sandy beaches along the
a significant increase in driven processes (photo- stantial reductions in nutrient rising and will continue to rise. frequent and stronger during height have not been detected. southern and eastern
winter river discharge and a synthesis and respiration), loads have occurred since the Storm surges are sensitive winter. The large natural For northern and eastern parts coastlines of the Baltic Sea
decrease in spring floods has which induces seawater pH 1980s, however, no large-scale to changes in atmospheric variability over the Baltic of the Baltic a slight increase is are especially vulnerable and
been observed lately. The oscillations. In the long term, effects on ecosystem status circulation and future changes Sea masks possible past and significant and extreme wave rising sea level will increase
total runoff to the Baltic Sea atmospheric CO2 increase will can be detected yet. In the are uncertain. future trends. height is projected. sediment transport.
may increase with warming raise seawater CO2 concentra- future, land-based nutrient
temperatures. tion and cause pH decrease. management will have greater
effect on loads than green-
house gases emissions.
12 13Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Indirect parameters Indirect parameters
Categories
Energy cycle
Indirect parameters: Water cycle
Carbon and nutrient cycle
Sea level and wind
Ecosystem Biota and ecosystems
Human activities
Services
Ecosystem parameters indirectly affected by climate change
Oxygen Microbial community Benthic habitats Coastal and migratory fish Pelagic and demersal fish Waterbirds Marine mammals Non-indigenous species
Oxygen concentration and processes In the Baltic Sea, many Coastal and migratory fish Fish of marine origin Most obvious effects of climate Grey and particularly ringed While shipping is the
is controlled by physical Bacterially-mediated processes benthic species exist at the respond to changes in tem- mainly respond to changes change on Baltic waterbirds seal breeding success will main driver of new non-
transport and remineralization as well as the occurrence of edge of their distribution, perature, ice-cover, salinity and in temperature, salinity, are range shifts in winter be reduced by decreased indigenous species (NIS)
of organic matter. Bottom pathogenic Vibrios are expected and even small fluctuations river-discharge. Spring and water stratification and (migratory birds stay closer to sea ice quality and quantity. introductions, climate change
water oxygen deficiency to increase with current envi- in temperature and salinity summer-spawning species (e.g. circulation influencing breeding areas). Food supply Harbour and grey seal related changes in abiotic
observed in a vast area of the ronmental changes. However, can impact their abundance, perch, cyprinids, pike) will ben- oxygen conditions. Actions (fish, bivalves) and breeding southern Baltic distribution environment may support
Baltic Sea is a consequence only small changes in bacterial biomass, and spatial efit from increasing tempera- to reduce eutrophication, conditions are influenced in will be reduced by flooding their establishment and range
of water column stratification biomass and growth were de- distribution. In concurrence tures, whereas autumn-spawn- anoxic conditions, and fishing, various ways. of haul-outs. Changed expansion. Increasing water
and eutrophication. Thus, tected during the past decades. with trophic cascades and ing (e.g. salmonids) may be while considering food-web temperature, stratification, temperature may favour
future oxygen availability will The potential genetic adapta- eutrophication, climate disfavoured. Future actions interactions will be important. prey distribution, quality and species of warm water origin,
depend on nutrient loads, tion to climate change and lack change might lead to major must consider eutrophication, quantity will affect marine and potential salinity decrease
while projected warming may of proper models including bac- changes in biodiversity and fishing, food-web interactions mammals, but aggregate will benefit NIS of freshwater
reinforce eutrophication. terioplankton make predictions ecosystem functions of and habitat exploitation, for effects are unpredictable. origin, impacting likely
for the future uncertain. benthic habitats. migratory fish also in rivers. estuarine ecosystems.
Marine protected areas Nutrient concentrations Ecosystem function
Climate change may impact and eutrophication Baltic Sea ecosystems provide
Marine protected areas Nitrogen and phosphorus an array of functions related to
(MPAs) via changes in abiotic pools are controlled by loads nutrient- and carbon circula-
environment causing diverse from land and atmosphere tion, biomass production and
changes in ecosystem and influenced by oxygen-sen- regulation. Climate impacts
structure and functions, thus sitive biogeochemical pro- ecosystem functions via
altering MPAs' conservation cesses. Future load changes temperature, water circula-
values. Changes are expected will have a stronger influence tion, salinity, river-discharges,
first in seal and water bird on nutrients than climate and solar-radiation. In the
populations, followed by change, even though pro- future, increased productivity,
potential large-scale changes jected warming will increase stronger impact of nutrients
in benthic habitats if possible nutrient cycling and reduce and reduced influence of pred-
salinity decrease starts bottom water oxygenation. ators will influence Baltic Sea
affecting the distribution of ecosystem functioning.
key species.
14 15Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Indirect parameters Indirect parameters
Categories
Energy cycle
Indirect parameters: Water cycle
Carbon and nutrient cycle
Sea level and wind
Human use Biota and ecosystems
Human activities
Services
Human use parameters indirectly affected by climate change
Offshore wind farms Coastal protection Shipping Tourism Fisheries Aquaculture Blue carbon storage Marine and coastal
Wind farms are the most The shorelines of the Baltic Shipping is primarily affected Climate change shapes the Most notable impacts to Baltic Sea aquaculture is capacity ecosystem services
significant offshore structures Sea vary from bedrock-dom- by ice and extreme weather, spatial and temporal distri- fisheries will take place in the dominated by open-cage Blue Carbon (BC) refers to Ecosystem services in the north-
in the Baltic Sea. Declining ice inated stable coasts in the and the potential for shipping bution of tourism resources northern Baltic Sea. Trawl rainbow trout farms with low the carbon marine organ- most and coastal semi-enclosed
cover and rising sea level can north to soft, sandy shores in will increase if the ice cover is within and between regions. fishing season will be extend- climate impact. Cultivation of isms sequester in oceanic areas with lower salinities will
affect offshore wind farms. the south, where periods of reduced. However, shipping The future competitiveness ed, trawling areas shifted blue catch-crops, including carbon sinks. Climate change be affected first. Most ecosystem
Offshore wind farms affect storminess cause coastal ero- intensity is more dependent of coastal and maritime towards the south and shal- plants and invertebrates, is effects on BC habitats, such services are expected to decline,
many oceanographic pro- sion. Declining ice cover and on market development than tourism in the Baltic Sea lower areas, target species increasing. Warmer condi- as effects on carbon sink ca- while only the cultural services,
cesses and have a substantial rising sea level increase the climate change. Regulatory region will be conditional to compositions shifted towards tions will promote offshore pacity and changed amount connected to recreation, could
effect on the structural and potential for coastal erosion. measures to decarbonise the adaptive capacity of the species preferring warmer locations and species diversi- of macrophytes, are expected gain from the climatic changes
functional biodiversity of the shipping are increasing and sector to climate change, waters, and winter-time fication. Industrial scale, land- to increase in the future, with due to longer summers and
benthic system. They account driving important adapta- changing consumer values, coastal fishing decreased due based aquaculture farms are associated effects on climate higher air and water tempera-
for 10 % of European offshore tions across the industry. natural and human-made to diminishing ice-cover. unlikely in rural parts due to change mitigation. tures. Other anthropogenic pres-
wind energy and are crucial hazards, and economic and their external resource- and sures could both offset positive
for reaching new energy and political disturbances. infrastructure dependents. and strengthen negative trends
climate targets. in ecosystem services supply.
16 17Direct parameters
Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Direct parameters Direct parameters
Authors Authors
Anna Rutgersson, Uppsala University, Sweden Christian Dieterich, Swedish Meteorological and Hydrological Institute (SMHI), Sweden
H.E. Markus Meier, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany,
Energy cycle and Swedish Meteorological and Hydrological Institute (SMHI), Sweden
Air temperature Water temperature
Energy cycle
Links to main policies:
HELCOM Baltic Sea Action Plan
UN Sustainable Development Goals 13 and 14
UN Convention on Biological Diversity
EU Green Deal
EU Marine Strategy Framework Directive (MSFD)
Linked parameters: Linked parameters: EU Water Framework Directive (WFD)
Water temperature, Large-scale atmospheric circulation, Sea ice, Solar Air temperature, Sea ice, Solar radiation, Stratification, Carbonate chemistry, Oxygen, Microbial community and processes, EU Maritime Spatial Planning Directive (MSP)
radiation, River runoff, Riverine nutrient loads and atmospheric deposition, Links to main policies: Benthic habitats, Coastal and migratory fish, Pelagic and demersal fish, Waterbirds, Non-indigenous species, Nutrient EU Habitats Directive
Waterbirds, Tourism UN Sustainable Development Goal 13 concentrations and eutrophication, Ecosystem function, Tourism, Aquaculture, Blue carbon storage capacity EU Strategy for the Baltic Sea Region (EUSBSR)
EU Biodiversity Strategy EU Biodiversity Strategy
Description What is already happening? What can be expected? Description What is already happening? What can be expected?
Since air temperature shows the clearest Mean change: An increase in air tem- Mean change: Air temperatures are As air temperature increases, also Mean change: Marginal seas around Mean change: Global ocean
response to the increased green-house perature is seen during the last century, projected to increase more in the Baltic water temperature rises1. Starting at the the globe have warmed faster than the temperatures are rising at accelerating
effect, the near-surface mean air with an accelerated increase during the Sea region than the global mean. Regional surface, the heat spreads downward global ocean2, and the Baltic Sea has rates7,8. Scenario simulations for the
temperature is often used as the main last decades1-3. Annual mean temperature scenarios project an annual mean near- through different processes and may warmed the most of all marginal seas2. Baltic Sea project a sea surface tempera-
indicator of a changing climate globally trends during 1876−2018 indicate that surface temperature increase over the warm up even the deep water of the Average surface-water temperature ture increase of 1.1°C (0.8-1.6°C, RCP2.6)
and regionally. Changes in temperature air temperature has increased more in Baltic Sea of 1.4°C (1.2-1.9°C, RCP2.6) to Baltic Sea. The ocean plays an important increased by +0.59°C/decade for 1990- to 3.2°C (2.5-4.1°C, RCP8.5)* by the end of
extremes may influence biological and the Baltic Sea region than globally. The 3.9°C (3.1-4.8°C, RCP8.5)* by the end this role for the climate because by far the 20183 and between +0.03 and +0.06°C/ this century compared to 1976-20059-12.
human activities much more than chang- increase is accompanied by large multi- century6, compared to 1976-2005. The largest amount of the heat from global decade for 1856-2005 in northeastern In all scenarios, sea surface temperature
es in average temperature. decadal variations, in particular during air temperature increase is larger in the warming is stored in the oceans. Due to and southwestern areas, respectively4. changes at the end of the century signifi-
winter, but the warming is seen for all North than in the South because of the their huge heat capacity, oceans respond cantly exceed natural variability.
seasons and is largest during spring. snow and sea-ice cover decline enhancing slowly, and moderate temperature Extremes: With reference to 2020,
absorption of sunlight by soil and water2. increases in the atmosphere. Oceans are the summer of 2018 was the warmest on Extremes: The RCP4.5 and RCP8.5
Extremes: During the recent decade, also important in providing moisture to instrumental record in Europe, and also scenarios project more tropical nights
record breaking heat waves have hit the Extremes: Larger warming is expect- the atmosphere, the more the warmer the warmest summer in the past 30 years over the Baltic Sea, increasing the risk of
region, with an increasing trend of warm ed for cold extremes than for the mean the water is. in the southern half of the Baltic Sea5, record-breaking water temperatures13.
spell duration4,5. A decrease is seen in winter temperature7. In summer, warm with surface-water temperatures 4-5°C
the length of the frost season and in the extremes are projected to become more above the 1990-2018 long-term mean.
number of frost days. pronounced. Warm extremes presently The heat wave has also been recorded in
with a 20-year return probability will bottom temperatures6.
occur around once every five years in
Scandinavia by 2071–21008.
Knowledge gaps Policy relevance Knowledge gaps Policy relevance
The variability in temperature and tem- Higher temperatures trigger marine For the projection of water temperatures Water temperature has profound effects
perature extremes are to a large extent heatwaves, and will have direct and in the Baltic Sea, regional climate models on the marine ecosystem. Climate
determined by the large-scale circulation indirect effects on habitats, species, and are needed. However, the effect of aero- change mitigation is the only way to
patterns. There is limited knowledge populations in terrestrial and aquatic sols in regional climate models has not counteract temperature increase. The
primarily concerning changes in large- ecosystems. Higher mean temperatures been investigated. More knowledge on best adaptation response available is to
scale atmospheric circulation patterns and increased number of heatwaves natural variability of Baltic Sea tempera- reduce environmental pressures to the
in a changing climate because of model will increase the risks of droughts and ture and its connection to large-scale Baltic Sea, thus building climate change
differences. forest fires. There is a need for better patterns of climate variability is needed. resilience. The protection of marine
urban planning, for example adapting The occurrence of marine heatwaves areas where the temperature increase is
building standards for warmer climate is projected to increase. However, their expected to be lower, so-called climate
and increasing urban green areas. Areas potential to affect the ecosystem in the refuges, focuses on areas where climate
such as Gotland have increased the Baltic Sea is not well known. change impacts are not contributing to
capacity of their desalination plants, to multiple stressors14,15. These could be-
ensure sufficient drinking water during come a last outpost for species affected
droughts. Further measures to better by climate change.
manage heat and drinking water need to
be implemented.
*) Changes in mean, 5th and 95th percentiles indicating *) Changes in mean, 5th and 95th percentiles indicating
the spread in an ensemble of 9 climate models. the spread in an ensemble of 9 climate models.
20 21Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Direct parameters Direct parameters
Authors Authors
Claudia Frauen, Leibniz Institute for Baltic Sea Research Warnemünde, (IOW), Germany Jürgen Holfort, Federal Maritime and Hydrographic Agency (BSH), Germany
Large scale
Anna Rutgersson, Uppsala University, Sweden
Florian Börgel, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany Energy cycle
H.E. Markus Meier, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany,
and Swedish Meteorological and Hydrological Institute (SMHI), Sweden
Sea ice
atmospheric circulation
Energy cycle
Links to main policies:
HELCOM Baltic Sea Action Plan
UN Sustainable Development Goals 13 and 14
UN Convention on Biological Diversity
EU Green Deal
Links to main policies: EU Marine Strategy Framework Directive (MSFD)
Linked parameters: HELCOM Baltic Sea Action Plan Linked parameters: EU Water Framework Directive (WFD)
Air temperature, Solar radiation, Precipitation, Wind UN Sustainable Development Goal 13 Air temperature, Water temperature, Solar radiation, Precipitation, Sea level, Wind, Waves, Sediment transportation, EU Maritime Spatial Planning Directive (MSP)
EU Strategy for the Baltic Sea Region (EUSBSR) Microbial community and processes, Benthic habitats, Pelagic and demersal fish, Coastal and migratory fish, Water- EU Habitats Directive
EU Green Deal birds, Marine Mammals, Coastal protection, Offshore wind farms, Ecosystem function, Shipping, Tourism, Fisheries, EU Strategy for the Baltic Sea Region (EUSBSR)
EU Biodiversity Strategy Aquaculture, Blue carbon storage capacity, Marine and coastal ecosystem services EU Biodiversity Strategy
Description What is already happening? What can be expected? Description What is already happening? What can be expected?
The climate of the Baltic Sea region is The NAO has high interannual variabil- In the future, the NAO is very likely In the northern regions of the Baltic Sea, Mean change: During the last 100+ Mean change: In the future, it is very
influenced by the large-scale atmospher- ity but shows no significant trend during to continue to exhibit large natural vari- ice is present every winter, while further years, ice winters have become milder, likely that the maximum sea-ice extent
ic circulation. The variability of the circu- the last century. After an increase from ations, similar to those observed in the south sea ice occurs only sporadically. As the ice season shorter (-18 days at Kemi/ will decrease (by between 6,400 (RCP4.5)
lation can be decomposed into various 1960 to 1990 (with more frequent wet and past. It is likely to become slightly more water effectively absorbs heat, whereas Bothnian Bay and -41 days at Loviisa/Gulf and 10,900 (RCP8.5) km2 per decade)4.
dedicated modes of variability: mild winters), the NAO index returned to positive (more frequent wet and mild sea ice mostly reflects it, the influence of Finland)1 and the maximum ice extent The thickness of level ice is also very
lower values and after 1990 the blocking winters) on average, as a response to of sea ice on the Baltic energy balance is has decreased by about 30% (6,700 km2 likely to decrease, but there are still
1. The North Atlantic Oscillation (NAO) pattern shifted eastwards16,17 and the global warming19. Trends in the inten- high. A sea-ice cover also limits the atmo- decade-1). Indices based on the total win- large uncertainties for the thickness of
describes the intensity of the west- duration increased, with more stationary sity and persistence of blocking remain sphere-ocean exchange and dampens ter ice volume show a decreasing trend ridged ice5. The number of days with ice
erly flow. A positive NAO is related circulation patters as a consequence18. uncertain23. Even under weak global surface waves. While air temperature has in the period 1985-2015 (more than 10%/ and length of the ice season are likely to
to mild, wet winters and increased However, there is low confidence in the warming the AMO is expected to respond the largest influence on the formation decade in many regions)2. decrease, but with considerable regional
storminess1-8. changes concerning blocking patterns19. very sensitively, that is, a shortening of and decay of sea ice, wind has a large differences in the magnitude6.
2. Atmospheric blocking occurs when The AMO warmed from the late 1970s time scale and weakening in amplitude24. influence on the spatial distribution and Extremes: The maximum ice extent
persistent high-pressure systems to 2014 as part of natural variability. deformation (ridging, rafting). in the Baltic Sea, including Kattegat, Extremes: Inter-annual ice variability
interrupt the normal westerly flow Recently, the AMO began transitioning to varies from year to year between 40,000 is likely to continue to be large, but the
over middle and high latitudes9,10. a negative phase again20. Paleoclimate and 420,000 km2. The probability of se- probability of severe to very severe
3. The Atlantic Multidecadal Oscilla- reconstructions and model simulations vere ice winters has decreased, an extent winters will likely decrease5.
tion (AMO) describes fluctuations in suggested that the AMO might change its larger than 300,000 km2 occurred in 16%
North Atlantic sea surface tempera- dominant frequency over time21,22. How- of the last 100 winters, compared to 3.3%
ture with a 50–90 year period11-15 ever, the impact of the AMO on Northern of the last 30.3
affecting the large-scale atmospheric European climate is independent of its
circulation15. frequency14,15.
Knowledge gaps Policy relevance Knowledge gaps Policy relevance
While climate models are able to The impact of anthropogenic greenhouse Sea ice as a brittle material is not well The importance of sea-ice change is high-
simulate the main features of the NAO, gas emissions might change the large- represented in numerical climate er in the northern part of the Baltic Sea,
its future changes may be sensitive to scale circulation that connects northern models7. The fact that ice dynamics, especially for ringed seals and shipping.
boundary processes, like e.g. strato- Europe with the North Atlantic region. like rafting and ridging, are not Shipping will be affected through less
sphere-troposphere interactions or Small changes in the flow would have well-represented also leads to large restrictions on routes and less need for
atmospheric response to Arctic sea ice large consequences for the climate in the uncertainties in sea-ice thickness icebreakers, but less ice cover on average
decline, which are not yet well represent- Baltic Sea region, i.e., more a maritime or and albedo (i.e., amount of sun light does not mean absence of severe ice win-
ed in many climate models19. Most global continental climate. reflected/absorbed). There is only limited ters nor of the presence of pack-ice/ridg-
climate models still underestimate the information about sea-ice thickness ing. Diminishing ice cover also increases
frequency of blocking over the Europe- and ice categories and long data sets for the risk and severity of coastal erosion
an-Atlantic sector19. these parameters are sparse. in vulnerable areas. A lack of ice cover
should have an influence on the planning
of coastal protection, and policies for this
may need to be adapted.
22 23Climate Change in the Baltic Sea Fact Sheet 2021 Climate Change in the Baltic Sea Fact Sheet 2021
Direct parameters Direct parameters
Authors Authors
Anna Rutgersson, Uppsala University, Sweden H.E. Markus Meier, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany
Salinity and
Thomas Carlund, Swedish Meteorological and Hydrological Institute (SMHI), Sweden and Swedish Meteorological and Hydrological Institute (SMHI), Sweden
Jan H. Reißman, Federal Maritime and Hydrographic Agency (BSH), Germany
Energy cycle
Solar radiation
Water cycle
Links to main policies:
saltwater inflows
HELCOM Baltic Sea Action Plan
UN Sustainable Development Goals 2 and 14 Links to main policies:
EU Green Deal HELCOM Baltic Sea Action Plan
Linked parameters: EU Water Framework Directive (WFD) Linked parameters: UN Sustainable Development Goal 14
Air temperature, Water temperature, Large-scale atmospheric circulation, Sea EU National Emissions Ceilings Directive (NECD) Stratification, Precipitation, River runoff, Carbonate chemistry, Sea level, Wind, UN Convention on Biological Diversity
ice, Stratification, Precipitation, Ecosystem function, Tourism EU Common Agricultural Policy (CAP) Oxygen, Microbial community and processes, Benthic habitats, Pelagic and EU Marine Strategy Framework Directive (MSFD)
EU Strategy for the Baltic Sea Region (EUSBSR) demersal fish, Coastal and migratory fish, Non-indigenous species, Ecosystem EU Strategy for the Baltic Sea Region (EUSBSR)
EU Biodiversity Strategy function, Aquaculture, Blue carbon storage capacity EU Biodiversity Strategy
Description What is already happening? What can be expected? Description What is already happening? What can be expected?
Solar radiation is the engine of the Multidecadal variations in solar radi- Future change is uncertain. Global Salinity is an important variable for Mean change: There are no statis- Mean change: An increase in river
climate system. Radiation emitted by the ation, called “dimming” and “brighten- climate models indicate an increase density, which controls the dynamics of tically significant trends in salinity, river runoff from the northern catchment
sun varies little. Hence, apart from the ing”, have been observed in Europe and in surface solar radiation, highest over currents in the ocean. Salinity also affects flow or MBIs on centennial timescales area will tend to decrease salinity, but a
variation with the time of the year and other parts of the world, especially in the southern Europe and decreasing towards Baltic Sea communities, for example since 1850, but pronounced multi- global sea level rise will tend to increase
day, radiation at the surface depends northern hemisphere1-3. Aerosol-induced north, but still showing a slight increase species distribution. Due to freshwater decadal variability, with a period of about salinity, because the water level above
largely on cloudiness. Total cloudiness multidecadal variations in surface solar over the Baltic Sea region. However, supply from the Baltic Sea catchment 30 years2-8. Model results suggest that the sills at the Baltic Sea entrance and
comprises clouds at all levels (low, radiation could be expected also over regional climate model runs could and the limited water exchange with the a decade of decreasing salinity, like the the saltwater imports from the Kattegat
medium, and high) and is related to the oceans4, but long-term measurements instead show a decrease in surface solar global ocean, surface salinity gradates 1983-1992 stagnation, appears approx- would be higher. A 0.5 m higher sea level
general atmospheric circulation as well are lacking. Satellite cloudiness trends radiation over the Baltic Sea region6. from > 20 g kg-1 in Kattegat to < 2 g kg-1 imately once per century due to natural would increase the average salinity by
as the water cycle. A cloud layer often since the 1980s differ for many areas but Unknown future aerosol emissions add in the Bothnian Bay. The dynamics of variability9. Baltic Sea salinity is also in- about 0.7 g kg-1 12. Due to the large un-
reflects 40% to 80% of incoming solar seem to agree on a decline over the Baltic to the uncertainty. the Baltic Sea are characterized by a fluenced by the Atlantic Multidecadal Os- certainty in projected freshwater supply
radiation. Atmospheric aerosols have a Sea region5. Records indicate weak but pronounced, perennial vertical gradient cillation with a 50–90-year period10. Since from the catchment area, wind and
smaller, but significant effect on solar significant negative trends (0.5–1.9% per in salinity. the 1980s, bottom salinity has increased, global sea level rise, salinity projections
radiation, both directly and indirectly, decade) for global as well as for northern Large, meteorologically driven saltwa- and surface salinity has decreased11. show a widespread trend, and no robust
through interaction with clouds. mid-latitude cloudiness. ter inflows, so-called Major Baltic Inflows changes have been identified13-16.
(MBIs), sporadically renew the deep Extremes: The frequency of MBIs
water with saline, oxygen rich water and shows no statistically significant trend Extremes: The frequency of MBIs is
this is the only process that effectively during instrumental (1886–2017) and projected to slightly increase17.
ventilates the deep water1,2. paleoclimate periods2,9.
Knowledge gaps Policy relevance Knowledge gaps Policy relevance
Multidecadal variations in surface solar Solar radiation influences biological ac- Due to the large natural variability and Salinity and the ventilation of the deep
radiation are generally not well captured tivity and ecosystems, through effects on uncertain changes in the regional water water with oxygen that is associated with
by current climate model simulations7,8. phytoplankton and algal blooms. Altered cycle, including precipitation over the MBIs, are important drivers of the Baltic
The extent, to which the observed solar radiation would either increase or Baltic Sea catchment area, in wind fields Sea ecosystem functioning and structure,
surface solar radiation variations are decrease biological activities (e.g., pho- and in global sea level, the confidence in including reproduction of commercially
caused by natural variation in cloudi- tosynthesis). Policy actions to reduce air future salinity projections is low14. Mod- important marine fish species, such as
ness induced by atmospheric dynamic pollution will impact solar radiation and elling data show that the north-south cod20,21. The distribution of freshwater
variability9,10, anthropogenic aerosol thus climate change, as reduced air pollu- gradient has changed with an increase and marine species and the overall
emissions2,8,11,12 or perhaps other causes, tion increases the solar radiation reaching in runoff in the North, and a decrease in biodiversity depends strongly on salinity
is not well understood. the surface. Reducing atmospheric aero- the South5. Not much is known about and oxygen concentrations20. Hence, the
sol particle concentrations is important changes in salinity composition and their salinity dynamics is a major factor for the
to improve air quality and public health. large decadal variability. Changes in total implementation of marine policies21.
Currently there is a lively debate related salt import have not been adequately
to geoengineering, including methods investigated. Changes in the large-scale
of increasing reflection of solar radiation circulation in the Baltic Sea are not well
back into space, to reduce its heating understood18,19.
effect on a global scale.
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