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9 May 2014, Mariehamn, Östersjöfonden
Förutsättningar, trender
och effekter av
klimatförändringar –
sammanfattning av
BACC II slutsatser
Hans von Storch
Helmholtz Zentrum Geesthacht
IPCC: Global temperature development
during “instrumental times”
Consensus among climate scientists
Bray, 2010
b)
Climate scientists agree more and more that
a) the world is warming („manifestation“)
and that this warming can not be explained without referring to
increased GHG levels („attribution“)
BACC as „regional IPCC“
BALTEX Assessment of Climate Change for the
Baltic Sea basin - BACC
An effort to establish which scientifically
legitimized knowledge about climate change
and its impacts is available for the Baltic Sea
catchment.
Approximately 80 scientists from 12 countries
have documented and assessed the published
knowledge in 2008 in BACC 1;
in 2014 BACC-2 comes out, with about 130
contributing authors.
The assessment has been
accepted by the intergovernmental HELCOM
commission as a basis
for its judgment and
recommendations.
Östersjöfonden, Mariehamn, 9 Maj 2014-
Principles
→ The assessment is a synthesis of material drawn
comprehensively from the available scientifically legitimate
literature (e.g. peer reviewed literature, conference
proceedings, reports of scientific institutes).
→ Influence or funding from groups with a political,
economical or ideological agenda is not allowed;
however, questions from such groups are welcome.
→ If a consensus view cannot be found in the above defined
literature, this is clearly stated and the differing views are
documented. The assessment thus encompasses the
knowledge about what scientists agree on but also identify
cases of disagreement or knowledge gaps.
→ The assessment is evaluated by independent scientific
reviewers.
Printed at
Östersjöfonden, Mariehamn, 9 Maj 2014-
BACC (2008) results – in short
→ Presently a warming is going on in the Baltic Sea region,
and will continue throughout the 21st century.
→ BACC considers it plausible that this warming is at least
partly related to anthropogenic factors.
→ So far, and in the next few decades, the signal
is limited to temperature and directly related variables,
such as ice conditions.
→ Later, changes in the water cycle are expected to become
obvious.
→ This regional warming will have a variety of effects on
terrestrial and marine ecosystems – some predictable such
as the changes in the phenology others so far hardly
predictable.
Printed at
Mariehamn, 9 Maj 2014Overall Östersjöfonden,
Summary
of BACC-2 (2013)
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New assessment finds results of BACC I valid
Significant detail and additional material has been found and assessed.
Some contested issues have been reconciled (e.g. sea surface temperature
trends)
Ability to run multi-model ensembles seems a major addition; first signs of
detection studies, but attribution still weak
Regional climate models still suffer from partly severe biases; the effect of
certain drivers (aerosols, land use change) on regional climate statistics
cannot be described by these models.
Data homogeneity is still a problem and sometimes not taken seriously
enough
The issue of multiple drivers on ecosystems and socio-economy is
recognized, but more efforts to deal with are needed
In many cases, the relative importance of different drivers, not only
climate change, needs to be evaluated.
Printed at
Mariehamn, 9 Maj 2014Overall Östersjöfonden,
Summary
of BACC-2 (2013)
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Estimates of future deposition and fluxes of substances like sulphur and nitrogen
oxides, ammonium, ozone, carbondioxide depend on future emissions and climate
conditions. Atmospheric factors are relatively less important than emission changes.
In the narrow coastal zone, where climate change and land uplift act together plant
and animal communities had to adapt to changing environment conditions.
Climate change is a compounding factor to major drivers of freshwater
biogeochemistry, but evidence is still often based on small scale. The effect of climate
change cannot be quantified yet on a Baltic Basin wide-scale.
Scenario simulations suggest that most probably the Baltic Sea will become more acid
in the future.
Increased oxygen deficiency, increased temperature, changed salinity and increased
acidification will impact the marine ecosystem in several ways and may erode the
resilience of the ecosystem.
Increasing need for adaptive management strategies (forestry, agriculture, urban
complexes) in the Baltic Sea Basin that deal with both climate change but also
emissions of nutrients, aerosols, carbondioxide and other substances.
Printed at
Air temperature
The warming of the low level atmosphere
is larger in the Baltic Sea regions than the
global mean for the corresponding period.
Warming continued for the last decade
 Not in winter
 Largest in spring
 Largest for northern areas
No recent ”stagnation” except for winter.
Data sets
Year
Winter
Spring
Summer
Autumn
Northern area
0.11
0.10
0.15
0.08
0.10
Southern area
0.08
0.10
0.10
0.04
0.07
1 Linear surface air temperature trends (K per decade) for the period 1871-2011 for the Baltic Sea
Basin. Northern area is latitude > 60°N. Bold numbers are significant at the 0.05 level.
Data updated for BACCII from the CRUTEM3v dataset (Brohan et al. 2006)
Same for
1871-2004
(BACC I):
Annual and seasonal mean surface air temperature
anomalies for the Baltic Sea Basin 1871-2011, Blue colour
comprises the Baltic Sea basin to the north of 60°N, and red
colour to the south of that latitude.
Climate science has done its homework for most of the global issues
Range of projected change of: Temperature – at the end of the century
Range of projected change of: precipitation amount – at the end of the century
Wind extremes 10yrv
4. Future climate change
Maximum wind
Marine ecosysteme
Higher Temperature are expected to go along with

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Stronger growth
Earlier plankton blooms
Modification of species composition
Possibly advantages for blue algae
Invading of foreign species
Threatening of ringed seals (loss of ice cover)
and lower salinity
 Changing species composition; immigration of new species
 Reduced oxygen supply in deeper waters, which may be associated with problems for fisheries
(cod)
 Changed distribution and composition of zooplankton (food for small fish and fish larvae) and
bottom-dwelling organisms.
Östersjöfonden, Mariehamn, 9 Maj 2014-
Detection and Attribution
→ Detection of non-natural influence on regional warming. Can be explained
only by increased greenhouse gas concentrations. Present trend consistent
with model scenarios.
→ Detection of non-natural component in trends of precipitation amounts;
present trends much larger than what is anticipated by models; thus no
consistent explanation for the time being.
→ Lack of studies on detection of changes in other variables
(e.g. snow cover, runoff, sea ice)
→ Lack of studies of the effect of other drivers (reduction of industrial aerosols,
land use change)
Printed at
Regional attribution
Observed CRU, EOBS (1982-2011)
Projected GS signal, A1B scenario
10 simulations (ENSEMBLES)
Observed and projected
temperature
trends (1982-2011)
The observed (grey) trends are
mostly consistent with what
the regional climate models
(green) suggest as response to
elevated GHG levels.
However, the observed
warming was in all seasons
larger than what the models
suggested.
Regional attribution
Observed 1972-2011 (CRU, EOBS)
Projected GS signal (ENSEMBLES)
Observed (grey) and projected
(green) precipitation trends
(1972-2011)
The observed changes are in all
seasons, except for fall (SON),
larger than those suggested by the
regional climate models.
The observed changes in winter
(DJF) , summer (JJA) und fall (SON)
are inconsistent with the models’
suggestion.
In fall (SON) observation and
projection even contradict each
other.
Climate science has provided suficient
knowledge for societies to decide about limiting
climate change
Yes,
- Climate is changing,
- We can not explain this change in terms of temperature not
without referring to elevated greenhouse gases
- When looking at change in general, global climate change is one
factors; others may be at work as well, sometimes dominantly so.
- Climate change represents a challenge for human societies and
ecosystems
- Climate change can be limited by limiting the accumulation of
greenhouse gases in the atmosphere.
Whether societies agree on joining to actually limit climate change is
legitimately a matter of policymaking, of values, of societal choices.
Independently of mitigation, a need for
adaptation remains – this is a regional and local
issue
We have not done our homework
- to study ongoing and possible future change.
- to separate the different causes for observed change.
Climate science needs to deal more with options of adaptation to
prepare for societal decisions.
The more successful the climate change limitation policy is, the less
adaptation is needed – but adaptation is needed, and is useful in any
case, if vulnerability is reduced.
The regional scientific community is asked to generate the needed
knowledge. The eventual decisions needed are again a matter of
policymaking, of values, of societal choices.