Transcript Scenario building in climate science

Scenario building
in climate science
Hans von Storch
Institute for Coastal Research
GKSS Research Center
U Lüneburg, 1.6.2006
Küstenforschung
GKSS, Geesthacht
• Beschreibung und Bewertung von gegenwärtigem
Kima und Kimawandel im Küstenraum.
• Ableitung von Szenarien des möglichen
zukünftigen Klimawandels im Küstenraum.
• Besonderes Augenmerk: Windbezogene Aspekte,
also Windkraft, Sturmfluten und Seegang.
• Vor allem: Nord- und Ostsee.
• Rekonstruktion vergangener und
gegenwärtiger Zustände und deren
Änderung
• PKMnP Zukünfte = plausible, konsistente,
mögliche aber nicht notwendigerweise
wahrscheinliche Zukünfte = Szenarios.
Outline
• What is a scenario?
• Scenarios of what? – anthropogenic climate
change
• Critical assumption for building scenarios –
emission of radiatively active substances into the
atmosphere
• Tools to construct climate change scenarios:
quasi-realistic climate models
• Tools for considering adaptation options:
regional models, impact models
What is a scenario?
• A scenario is a consistent, plausible description
of a possible not necessarily probable future.
• It often takes the form of a conditional prediction,
i.e., a prediction which utilizes assumptions
about a few critical, often intrinsically
unpredictable developments.
• When all conditional predictions agree, it is an
unconditional prediction (i.e., there will be a
warming)
What is a scenario good for?
• Scenarios allow for the exploration of the
availability of options and the usefulness of
actions.
• Scenarios help to identify developments which
should be avoided or aimed at.
• Ideally, a series of different, partially inconsistent
scenarios is constructed so that the full space of
options can be explored.
• Scenario open minds for unexpected
developments (which sometimes scare people).
Scenarios of what?
• Climate = the statistics of weather,
usually described by probability density
functions, in particular by
- their moments (e.g., mean, std deviation,
covariances),
- percentiles and return values,
- spatial characteristics (e.g., EOFs),
- temporal characteritsics (autocovariacne
function, spectra)
Scenario building
• Construction of scenarios of emissions.
• Construction of scenarios of
concentrations of radiatively active
substances in the atmosphere.
• (Ok – not quite exact; aerosols …)
• Simulation of climate as constrained by
presence of radiatively active substances
in the atmosphere (“prediction” of
conditional statistics).
Scenario building
1. Simulation with global models, which describe
several compartments of the global earth
system – relatively coarse spatial grid
resolution (e.g., 200 km)
2. Simulation with regional models, often with
only one or a few compartments (mostly
atmosphere) – relatively high spatial grid
resolution (e.g., 50 km)
3. Simulation with impact models – a large varitey
of different systems, e.g., storm surges or
ocean waves.
“SRES” Scenarios
SRES = IPCC Special Report on
Emissions Scenarios
A1
A world of rapid economic growth and rapid
introduction of new and more efficient technology.
A2
A very heterogeneous world with an emphasis on
family values and local traditions.
B1
A world of “dematerialization” and introduction of
clean technologies.
B2
A world with an emphasis on local solutions to
economic and environmental sustainability.
“ business as usual ” scenario (1992).
IPCC, 2001
IS92a
SRES scenarios
4CO2
3CO2
2CO2
Components of the climate system. (Hasselmann, 1995)
Quasi-realistic climate models …
… are dynamical models, featuring discretized equations of the type
dΨ k
  Pi ,k (k )
dt 20 proxies
Are
i enough to reconstruct the global mean temperature?
with state variables Ψk and processes Pi,k.
The state variables are typically temperature of the air or the ocean, salinity
and humidity,
wind and
Do temperature
andcurrent.
precipitation proxies yield the same NAO reconstruction?
… because of the limited resolution, the equations are not closed but must be
closed by “parameterizations”, which represent educated estimates of the
expected effect of non-described processes on the resolved dynamics,
conditioned by the resolved state.
atmosphere
ocean
Global scenarios of the
air temperature change
(in K) at the end of the
21st century, as
determined with a global
climate model forced
with A2 and B2
emissions. Courtesy:
Danmarks
Meteorologiske Institut.
Typical different
atmospheric
model grid
resolutions with
corresponding
land masks. T42
used in global
models.
(courtesy: Ole
BøssingChristensen)
temperature
Agreement among 7 out of a total of 9 simulations
Giorgi et al., 2001
TAR (2001) „regional development“
scenarios A2 and B2.
precipitation
Agreement among 7 out of a total of 9 simulations
Giorgi et al., 2001
TAR (2001) „regional development“
scenarios A2 and B2.
Regional atmospheric modelling: nesting into a global state
Typical
different
atmospheric
model grid
resolutions
with
corresponding
land masks.
50 km grid
used in
regional
models
(courtesy: Ole
BøssingChristensen)
Temperature change (in K) for winter (DJF) between the periods 1961-1990 and
2071-2100 according to the SRES A2 scenario.
A2 - CTL: changes in 99 %-iles of wind speed (6 hourly, DJF): west wind
sector selected (247.5 to 292.5 deg)
HIRHAM
RCAO
REMO5
Woth, pers.comm.
CLM
Estimated changes according to IPCC cenario A2 in 20702100 relative to 1960-1990; CLM model
(Rockel, per. comm.)
GCM (CTL: 1961 - 1990)
(A2:
2071 - 2100)
series of RCM runs
Run of the TRIM surge-model
with a series of RCM forcing
SLP & wind
components
dynamical downscaling of water
level / North European shelf sea
Woth, pers.comm.
Projections for the future / surge
meteorological forcing: HIRHAM / RCA
Differences in inter-annual
percentiles of surge / A2 - CTL:
HIRHAM
Woth, pers.comm.
Differences in inter-annual
percentiles of surge / A2 - CTL:
RCA
“Localisation”: From the coast
into the estuary
St Pauli
2030
2085
Empirical transferfunction:
German Bight
> St Pauli
Grid box “Cuxhaven”
SREs emission scenarios: Impact on global sea level
IPCC, 2001
PRUDENCE
regional scenario
Nur Effekt von Klimaveränderungen,
nicht von Veränderungen der
Morphologie der Tideelbe.
Scenarios
2030, 2085
Flood risk in Hamburg
Press release
30 October 2005
"The Calm before the Storm Storm surges in the North Sea could become more
dangerous from the middle of the century.
Scientists from the Institute for Coastal Research of the
GKSS Research Centre Geesthacht in Germany have
analysed the past history of storms and storm floods in the
North Sea region, and used models to investigate future
changes. Their result: human-induced climate changes will
lead to higher storm surges along the German, Dutch and
Danish North Sea coasts but current storm surges are not
influenced by human-induced climate change."
So far, we had …
• This was an example of scenarios form
the global to the local – which result in
unconditional forecasts of elevated future
storm surge heights related to elevated
concentrations of greenhouse gases in the
atmosphere.
• But is this the complete story for people
living in Hamburg and their concern for
storm surges?
Hamburg – Storm surges
Difference St. Pauli - Cuxhaven
Hamburg – Storm surges