7. September 2015 - School of Earth and Environmental Sciences, Seoul National University
BACC: Assessing
knowledge of regional
climate change - the
example of the Baltic
Sea region
Hans von Storch
Helmholtz Zentrum Geesthacht
Overview
1. The global state of affairs, consolidated knowledge,
IPCC, beliefs
2. The Baltic Sea region state of affair – the BACC (II)
assessment.
3. Major scientifically open questions
4. Regionalization of BACC assessment
IPCC: Global temperature development
during “instrumental times”
Consensus among climate scientists
b)
Bray, 2013
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“)
IPCC presents and assesses the knowledge about
climate change and climate impact on the global and all
large regions (such as Europe).
BACC is a little cousin of IPCC doing something similar
but only for the Baltic Sea region.
The two concepts are broadly similar, but deviate in
some significant ways, in particular the non-involvement
of governments by BACC.
5
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 May 2015, BACC-2 came out, with
141 contributing authors.
The assessment has been
accepted by the intergovernmental HELCOM commission
as a basis for its judgment
and recommendations.
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
BACC–1 (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
Summary of BACC-2 (2015)
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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
Overall Summary of BACC-2 (2015)
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Estimates of future deposition and fluxes of substances like sulphur , nitrogen
oxides, and carbondioxide depend on future emissions. Atmospheric factors
are less important than emission changes.
In the narrow coastal zone plant and animal communities have to adapt to
changing climate and to land uplift.
Climate change is a compounding factor for freshwater biogeochemistry. 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.
summer
r
winter
r
Range of projected changes at the end of the 21st century: Temperatur
summer
r
winter
r
Range of projected changes at the end of the 21st century: precipitation amounts
summer
r
winter
r
Wind extremes 10yrv
Range of projected changes at the end of the 21st century: Maximum wind
Marine ecosysteme
Higher Temperature are expected to go along with






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.
Detection and Attribution
→ Detection of non-natural influence on regional warming. Can be explained
only if increased greenhouse gas concentrations contribute. 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
Climate science has provided sufficient
knowledge for societies to decide about limiting
climate change
Yes,
- Climate is changing,
- We can not explain this change in terms of temperature without
referring to elevated greenhouse gases
- When looking at change in general, global climate change is one
factor; 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
- studying jointly ongoing and possible future change.
- separating the different causes for observed change.
Climate science needs to deal more with options of adaptation for
preparing 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, because of reduced vulnerability.
The regional scientific community is asked to generate the needed
knowledge. Again, the eventual decisions are a matter of
policymaking, of values, of societal choices.
Knowledge gaps
1. The issue of multiple climate change drivers (aerosols, landuse incl. urbanization)
2. The issue of multiple pressures on ecosystems and economy
(eutrophication and related algae blooms, climate change,
pollution, but also shipping and off-shore wind power and
other off-shore activities, tourism, natural conservation and
agriculture, fisheries and pollution)
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.
Barkhordarian, pers. comm.
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.
Barkhordarian, pers. comm.
Perspectives
- Regionalization of BACC assessment
Have short version in national languages,
with specification of change in in different
countries (in prep. Germany, Poland,
Belarussia)
- Assessing knowledge about climate,
climate change and impacts in other
regions of the world:
• Metropolitan region of Hamburg
• North Sea region (NOSCCA)
• Yellow Sea region