Transcript 1404_Klimamodeller_U..

Climate models and
climate scenarios
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Climate models
IPCC
Climate scenarios (SRES,RCP)
The future according to the scenarios
Bjørn H. Samset - Forsker, CICERO
[email protected] | kollokvium.no
Key questions:
• What is a climate model and how
can we use it?
• How do we design a climate
scenario and what can we learn
from it?
• What do the current scenarios
tell us?
Bjørn H. Samset | [email protected] | kollokvium.no
Bjørn H. Samset | [email protected] | kollokvium.no
Climate models and
scenarios
• Climate models simulate the processes and interactions
in the climate system.
• Many different types of models exist, with varying degree
of detail and complexity.
• When used in combination with emission scenarios such
models may also be used to predict the future climate.
Purpose of climate models
• Provide inputs to assessments of the current state of
climate science
• Explore the consequences of a current theory
• Test a hypothesis about the observational system
• Test a hypothesis about the calculational system
• Provide homogenized observational datasets
• Conduct thought experiments about different climates
Help us see if we understand the climate,
and help us decide what to do about climate change.
Model = physics + chemistry + geophysics + meteorology +
mathematics + observations + boundary conditions +
PhD students + intuition + …
Climate models
• A mathematical representation of the
climate system
– With different levels of physical complexity
– and resolution (spatial and temporal)
Increasing model complexity
Simple climate
model (SCM)
Global circulation
model (GCM)
Earth system
model
Regional climate
model (RCM)
Increasing
resolution
Simple one-layer atmosphere
http://www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model/
Energy balance model
Bjørn H. Samset | [email protected] | kollokvium.no
Climate models
• The simplest climate models are energy
balance models
– These models allow us to test the
temperature response to e.g. a change in CO2
concentrations
• If we want our climate models to be able
to:
– reproduce historical climate (last 100yrs or so)
– replicate natural variability of current
climate...
• …then more complex models are required
Global surface temperature evolution:
Trend (from CO2, methane, aerosols, …)
+ natural variability (ENSO, volcanoes, solar…)
Hansen, J., R. Ruedy, Mki. Sato, and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004
Bjørn H. Samset | [email protected] | kollokvium.no
General circulation model
(GCM)
General circulation model
(GCM)
From: http://www.climate.be/textbook/
Major natural and anthropogenic processes
and influences on the climate system
addressed in models
RH Moss et al. Nature 463, 747-756 (2010) doi:10.1038/nature08823
Examples:
Chaos!
GCMs let us probe the response of the atosphere to
some kind of kick
Case
Description
CO2
CO2 concentration increased 286 ppm  379 ppm
CO2x2
CO2 concentration doubled 286 ppm  572 ppm
Solar
Solar constant increased with 2 %
CH4
CH4 concentration increased 805 ppm  1774 ppm
CH4x2
CH4 concentration increased 805 ppm  2745 ppm
CH4x5
CH4 concentration increased 805 ppm  5650 ppm
SO4
SO4 concentration increased from preindustrial level to present level
SO4x5
SO4 concentration increased 5 times the change from preindustrial
present level
BC
Black carbon concentrations increased from preindustrial level to
present Level
BCx10
Black carbon concentration increased 10 times the change from
preindustrial level present level
BC@xxx
Total black carbon burden change inserted at 850mb, 750mb, 650mb
or 550mb respectively with 10 times the change from preindustrial
level to present level.
Kvalevåg, Samset and Myhre, GRL, 2013
Climate model setup example
• Download model from NCAR
• Set up and compile on abel supercomputer, 64 CPUs parallell
• Define a «case»:
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Resolution
Concentration of climate gases
Simulate ocean, atmosphere, ice, land, …? (On/off/prescribed/…)
Constant or changing with time?
Number of timesteps, how long to run
Compile and run. Our setup uses 24-48h per 10 simulated years
Move output (hundreds of GB) from abel to local analysis computer
Analyse, do science…
Typical usage: One «baseline» case where nothing changes, then
others where one or more parameters are changed. Look at the
difference.
Work in progress:
Climate impact of sea ice change
Climate modelling for other uses:
Nuclear war
Challenges
• The more complex the model, and the higher the resolution,
the more CPU and storage it requires
• Some components of the climate system are especially
difficult to model
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Clouds
Tropical storms
Land-surface processes
Winds, waves and currents
Other greenhouse gases (especially H2O and O3)
• What if the real climate is non-linear? I.e. if there are
sudden changes that our equations don’t capture?
All models are wrong – but some are more wrong than
others!
Model validation:
Do they reproduce observations?
IPCC = Intergovernmental
Panel on Climate Change
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Established in 1988 (after a process that more or less started in 1958)
Mandate: Report from the scientific literature
Participants: WMO + UNEP nations
Plenum = National delegates
3 working groups (climate system, impacts/adaptation, mitigation)
IPCC: Main reports
WG I
The Physical
WG II
Impacts, Adaptation
Science Basis
and Vulnerability
Hva skjer med klimaet
og hvorfor?
• Technical summary
• Summary for Policymakers
Hvordan merker
vi det?
WG III
Mitigation of
Climate Change
Hva kan vi gjøre for
å begrense det?
• Technical summary
• Summary for Policymakers
• Technical summary
• Summary for Policymakers
Synthesis Report
Synthesis Report: Summary for Policymakers (20 pages
negotiated text)
Bjørn H. Samset | [email protected] | kollokvium.no
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AR5: WG1 – Hva skjer+
Bjørn H. Samset | [email protected] | kollokvium.no
AR5: WG2 – Hvordan merker vi det?
Bjørn H. Samset | [email protected] | kollokvium.no
AR5: WG3 – Hva kan vi gjøre med det?
Bjørn H. Samset | [email protected] | kollokvium.no
Bjørn H. Samset | [email protected] | kollokvium.no
Scenarios
• According to the Forecasting Dictionary, a
scenario is “a story about what happened
in the future”
• Best guess projections?
• Internally consistent stories?
• Focus on economic and social
development, emissions, radiative forcing
or climate signal (e.g. temperature)?
Scenarios
• How do we strike a balance between
– prediction - believing that we can see past
uncertainties when in fact we can't…
– …and paralysis - letting the uncertainties
freeze us into inactivity
http://www. wired.com/wired/scenarios/build.html
Why scenarios?
• The purpose of scenario planning is not to
pinpoint future events, but to highlight
large-scale forces that push the future in
different directions.
• It's about making these forces visible, so
that if they do happen, the planner will at
least recognize them.
• It's about helping make better decisions
today.
Long fuse - big bang
• How do we decide what kind of career path to pursue
when it's not clear what industries will exist in 10 or 15
years? How do we plan our children's education when
we can't know what sort of society they'll live in?
Questions like these are known as "long fuse, big
bang" problems.
– Whatever you decide to do will play out with a big bang often a life or death difference to an organization - but it
can take years to learn whether your decision was wise or
not.
• Worse yet, such questions don't lend themselves to
traditional analysis; it's simply impossible to research
away the uncertainties on which the success of a key
decision will hang.
Simple «scenarios»
Assume that we eventually manage to cut 100% of CO2 emissions…
100% kutt – i dag
100% kutt – i dag
-5% i året – i dag
-3% i året – i dag
-1% i året – i dag
-3% i året – i dag
-3% i året – fra 2020
-3% i året – fra 2030
-3% i året – fra 2040
P. Friedlingstein et al, Nature Climate Change (2011), DOI: 10.1038/NCLIMATE1302
Bjørn H. Samset | [email protected] | kollokvium.no
Simple «scenarios»
Assume that we eventually manage to cut 100% of CO2 emissions…
100% kutt – i dag
Allerede i år 2100 ser vi
0.25 grader forskjell for
hvert tiende år vi utsetter
kutt-start – og denne
forskjellen holder seg
frem til år 2300.
100% kutt – i dag
-5% i året – i dag
-3% i året – i dag
-1% i året – i dag
-3% i året – i dag
-3% i året – fra 2020
-3% i året – fra 2030
-3% i året – fra 2040
P. Friedlingstein et al, Nature Climate Change (2011), DOI: 10.1038/NCLIMATE1302
Bjørn H. Samset | [email protected] | kollokvium.no
Even small emissions matter
What if we «only» cut by 90%?
90% kutt – i dag
-5% i året – i dag
-3% i året – i dag
-1% i året – i dag
-3% i året – i dag
-3% i året – fra 2020
-3% i året – fra 2030
-3% i året – fra 2040
P. Friedlingstein et al, Nature Climate Change (2011), DOI: 10.1038/NCLIMATE1302
Bjørn H. Samset | [email protected] | kollokvium.no
Lyst til å leke?
MAGICC/SCENGEN
http://www.cgd.ucar.edu/cas/wigley/magicc/
http://www.magicc.org/
Bjørn H. Samset | [email protected] | kollokvium.no
Model resolution for IPCC
main reports
IPCC AR5: CMIP5
Realistic scenarios highlight the
«corners» of possible futures
• The aim is to find the “corners” of possible
futures.
• These “corners” are exaggerations - limits of
what is possible.
• Therefore, good scenarios will almost be
caricatures.
• IPCC AR4: Special Report: Emission
Scenarios (SRES)
• IPCC AR5: Representative Concentration
Pathways (RCPs)
IPCC AR4/SRES
Scenario families
Very rapid economic growth, low population
growth and rapid introduction of new and more
efficient technology. Major underlying themes
are economic and cultural convergence and
capacity building, with a substantial reduction in
regional differences in per capita income.
A very heterogeneous world. The underlying
theme is that of strengthening regional cultural
identities, with an emphasis on family values
and local traditions, high population growth,
and less concern for rapid economic
development.
A2
B2
A world in which the emphasis is on local solutions
to economic, social, and environmental
sustainability. It is again a heterogeneous world
with less rapid, and more diverse technological
change but a strong emphasis on community
initiative and social innovation to find local, rather
than global solutions.
Bjørn H. Samset | [email protected] | kollokvium.no
A1
B1
A convergent world with rapid change in
economic structures, "dematerialization" and
introduction of clean technologies. The
emphasis is on global solutions to
environmental and social sustainability,
including concerted efforts for rapid technology
development, dematerialization of the
economy, and improving equity.
SRES
Bjørn H. Samset | [email protected] | kollokvium.no
AR5
RCP X.X:
X.X is approx.
final climate
forcing
Bjørn H. Samset | [email protected] | kollokvium.no
Integrated Assessment Models
Bjørn H. Samset | [email protected] | kollokvium.no
Fremtidige endringer:
Pathways (RCPs)
Bjørn H. Samset | [email protected] | kollokvium.no
«Hvor varmt blir det?»
To ting vi må vite:
1) Hvor mye varmes
jorden på lang sikt
for hver dobling av
CO2-konsentrasjon?
Dette kan vi prøve å
forstå.
2) Hvor mye CO2 m.m.
kommer vi til å slippe
ut?
Her må vi lage
scenarier.
Bjørn H. Samset | [email protected] | kollokvium.no
Fremtidige endringer:
Hva vi kan forvente?
Bjørn H. Samset | [email protected] | kollokvium.no
Fremtidige endringer:
Hva vi kan forvente?
Bjørn H. Samset | [email protected] | kollokvium.no
Hva blir konsekvensene?
• Villere vær -> flere ekstremhendelser -> mer
naturskade -> ressurser bundet opp til å holde
samfunnet gående
• Varmere -> mer tørke -> dårligere matproduksjon
-> sult i utsatte områder -> politisk ustabilitet
• Havnivåstigning -> problemer for kystområder
og utsatte øyer -> flyktningestrømmer
• Endret monsunmønster -> ferskvannsproblemer
i Sørøst-Asia -> sult -> politisk ustabilitet
• …
Verden greier seg. Vårt samfunn er derimot bygget på
en hittil veldig stabil gren. Denne er nå omtrent saget
over.
2o varmere? Store konsekvenser.
4o varmere? Uante konsekvenser.
6o varmere? ….
Bjørn H. Samset | [email protected] | kollokvium.no
Tipping points?
Bjørn H. Samset | [email protected] | kollokvium.no
Bjørn H. Samset | [email protected] | kollokvium.no
Bjørn H. Samset | [email protected] | kollokvium.no
Conclusions:
Climate models are invaluable tools – we just
need to know their limits
• A climate model is a
Key questions:
mathematical model of the
• What is a climate model and how
climate system, with some
can we use it?
degree of complexity
• How do we design a climate
scenario and what can we learn
• A climate scenario is a
from it?
guess about future emissions,
• What do the current scenarios
consumption etc., that we
tell us?
feed to the climate models
• Current scenarios (SRES, RCP) put us on a path towards a global
temperature increase of 2-5 degrees by 2100
Bjørn H. Samset | [email protected] | kollokvium.no
Does IPCC provide us with a
«Scientific Truth?»
• IPCC mandate: Report from the scientific
literature:
– ”Policy relevant, but not policy prescriptive”
• Do “scientific truths” exist?
• Science as a ”structured conversation”:
– Research  manuscript  review 
accepted/revise/rejected  revised manuscript 
published manuscript!
– Manuscript/comments … publish!
–…
• IPCC reports from this “conversation”
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Some observations
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IPCC will always “lag” behind the research frontier.
The language of IPCC is consensus oriented.
IPCC will warn against potentially dangerous events.
Single studies will have limited impact on IPCC
conclusions.
• The uncertainty tends to be
skewed with a higher probability
for worse realizations.
• New report in 2013/2014!!!
http://kollokvium.no/2011/10/13/ipcc-femte-rapport/
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Climate scenarios