Transcript Slide 1

CESD
SAGES
Scottish Alliance for Geoscience, Environment & Society
Launch
25th May 2007, Royal Society of Edinburgh
Centre For Earth System Dynamics
My Vision for the CESD in SAGES
Prof. Simon Tett, Chair of Earth System Dynamics:
University of Edinburgh
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Why did I join SAGES?
• Exciting possibility of helping set up major new initiative
• Knew that there were several good researchers in
climate change and carbon cycle active in Scotland
• Attracted by idea of multi-institution, multi-disciplinary
collaboration rather than competition and focus on
particular disciplines.
– Earth system is broad problem. Needs multiple skills to make
progress
• Liked idea of broad hinterland. (“Society”, Glaciology,
paleo-climate, land processes, land-carbon, satellite
observations etc)
• Felt it was time to do something different from current job
at Met Office & Edinburgh a good city, for me and my
family, to live in.
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Models
• Encapsulate our knowledge of the processes
and physics that drive the Earth System.
• Are uncertain
– Basic equations are well known but large scale
modelling of various processes such as convection is
uncertain.
• Can be used to predict the future and
understand/interpret the past
• Are chaotic. (Sensitive to initial conditions)
• Need to be tested.
– Are they fit for purpose?
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Emergent Phenomenon
• Interested in “Emergent Phenomenon”
• Not interested in detailed, and
unpredictable, evolution of state.
– How much warming will there be?
– How will hydrological cycle change?
– Will the number of severe storms change?
– Etc….
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Proxy Temperatures suggest late
20th century very unusual
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Instrumental temperatures show a
warming of about 0.7K since 1900
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Strong evidence that observed temperature
changes over the last century are due to
human effects
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Estimates of Climate Sensitivity
using models and observations
From IPCC
CH9, after
Hegerl et al.,
nature 2006
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What does the future hold?
IPCC multiFrom model
IPCC. Ranges are broad and
overlap one another (scenario “choice” vs
ensemble
understanding
of the natural world.)
Ensemble of “perturbed physics”
models showing large
uncertainty range of future
warming. Which are right?
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Carbon cycle
How to constrain this?
Have measurements of
CO2 concentration and
know about observed
climate
change/variability. Can
we use this to estimate
carbon feedbacks. BUT
don’t know sources
well…
From Friedlingstein et al, 2006. Plots shows additional CO2 from
feedbacks between climate change and carbon cycle. Values vary
between 25 and 225 ppm at 2100 mostly due to land-carbon cycle
feedbacks.
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What leads to uncertainty in Future
Change
• Future emissions of CO2 & other trace gases and aerosols
• Feedbacks
– Physical: Clouds, water vapour, ice, snow.
• Biosphere: Will the earth system continue to be a sink for CO2 or will
it be a source?
• Ocean – sets the timescale.
• First order effect (will world warm by 1 or 10 K) by end of 21st Century.
Both seem very unlikely. 10K would be “catastrophic climate change”
and requires very strong physical & biological feedbacks.
• My personal research aim is see to what extent, if any, observations
can rule out strong physical & biological feedbacks leading to warming
greater than about 4-5 K.
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TOA fluxes from ERBE vs
models
Changes in Top of Atmospheric fluxes are related to (fast) feedbacks. See Forster
and Gregory. Suggests low feedback and thus that models are too sensitive.
(Could be issues with data as well…)
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Last 1000 years
Are uncertainties in reconstructions so large as to preclude any significant
constraints?
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My Challenge
– Bring observations together with models to:
•
•
•
•
Test models (been done).
Quantify uncertainties.
Constrain the future.
Improve models (very hard).
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Regional changes & modes of
variability.
• Thermohaline circulation
– Lots of resources in this mainly due to concerns about its rapid
shutdown. Impacts global (NH cooling, SH warming) with largest impact
in Nth. Atlantic.
• North Atlantic Oscillation.
– Huge impact on European climate. Warm/wet winter vs cold/dry winters.
Some work shows it can be affected by tropical volcanic eruptions.
• El Nino/Southern Oscillation
– Huge source of climate variability in the tropics and extra-tropics.
Predictable up to about a year ahead. May have an influence on
European climate. Coupled atmosphere/ocean mode.
• General question. How will these modes change in a different
climate? What is the reason, in the models, for the changes? Are
they robust/realistic? How will their impacts change?
•
Warmer climate, in models, leads to, on average, drier summers
and wetter winters. +NAO (dry winter) could then cause serious
water shortages in the UK. Summer 2006 as example.
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Impacts & Extremes
• Policy relevant & what society needs to know.
• How to link to users/stake holders?
• Meteorology -> society and society->meteorology (what
are the important changes that generate impacts?).
• Need good metrics of natural variability in these so that
can decide if possible future climate changes important.
• My personal view is that impacts work needs more
exploration, range of models (“traceable hierarchy”) and
disciplines to provide good and robust answers.
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Extremes
• Extreme events are, by definition, rare
– What is natural variability in extreme events?
– Will GHG driven response overwhelm natural variability?
– Depends on type of event. Hot summers vs severe storms
UK SEVERE STORMS IN OND (1920-2004)
(> +/- 10 hPa in 3 hours)
(1959-2004: r =+0.34)
UK SEVERE STORMS
3.5
Number of UK severe
storms per year. (1/3 storm
= 1 severe storm in a
region). Multi-decadal
variability. Preliminary
results from Rob Allan
NUMBER OF STORMS
3
2.5
2
1.5
1
0.5
0
1920
1930
1940
1950
1960
YEARS
1970
1980
1990
2000
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Assessing Recent Change
Obs trend (K/dec) X where outside max abs 50-year
trend from Natural. + where outside max trend.
Recent changes outside nat var over
large parts of world. Suggest possible
impacts on natural systems
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Earth System Modelling Strategy
for SAGES
• Run HadCM3 on a cluster. Allows community to develop
experience and explore a variety of problems.
– HadCM3 no longer “state-of-the-art” but still a good model and
on a cluster will allow us to explore 1000 year timescales.
• Move to SAGES/HadGEM3 ESM (being developed now)
when it is ready.
– For work on a cluster will need a “fast” version.
• Start using HadGEM/HiGEM on Hector (new national
super-computer facility).
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Earth System Modelling Strategy
for SAGES
• Need to link with Hadley Centre and NCAS.
– We need to be part of, and contribute, to a UK community.
• How to use/organise community to coherently improve
models. Particularly an issue for a distributed community
like SAGES.
– How do we build on each others work?
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Final thought
• The scientific challenge is great and
society needs answers soon….
– Reasonable models today are better than
excellent models in 50 years.