Transcript Talk 5 - Research needs for decadal to centennial climate prediction

Research Needs for Decadal to
Centennial Climate Prediction:
From observations to modelling
Julia Slingo, Met Office, Exeter, UK
&
V. Ramaswamy. GFDL, Princeton, USA
Climate Change Projections and
Uncertainties
IPCC AR4
Quantifying uncertainties –
setting research priorities
2020’s
Improved model
physics e.g.
clouds
25
2080’s
Winter rainfall in south east
England
22
Benefits of initialisation
for near-term
35
projections
43
Higher resolution
global models
15
31
9
Natural Variability
Carbon Cycle
Downscaling
Model Uncertainty
Increased
20of earth
understanding
system processes –
more uncertainty?
Challenges for Centennial
Projections:
Earth System Modelling
Moving from Climate to Earth System Models:
Balancing the carbon cycle
Atmospheric circulation and radiation
Climate Model
Sea Ice
Ocean circulation
Land physics
and hydrology
Atmospheric circulation and radiation
Allows interactive CO2
Earth System
Model
Sea Ice
Ocean ecology and
biogeochemistry
Ocean circulation
Plant ecology and
land use
Land physics
and hydrology
Carbon-climate feedback and
centennial climate change
More Earth System Modelling challenges
• How can we reduce the uncertainties in current estimates
of the carbon-climate feedback?
• How do missing or poorly represented processes such as
the nitrogen cycle, plant adaptation to climate change,
vegetation dynamics, and plankton dynamics affect current
model results?
• What other biogeochemical feedbacks involving methane,
ozone and aerosols play a significant role on the centennial
timescale?
• How can Earth System Modelling inform decision-making
when climate change is one of many drivers for
environmental change (e.g. food security, water resources
and quality, biodiversity, air quality)?
Earth System Modelling:
Combining the needs of adaptation and mitigation
Quantifying uncertainties –
setting research priorities
2020’s
Improved model
physics e.g.
clouds
25
2080’s
Winter rainfall in south east
England
22
Benefits of initialisation
for near-term
35
projections
43
Higher resolution
global models
15
31
9
Natural Variability
Carbon Cycle
Downscaling
Model Uncertainty
Increased
20of earth
understanding
system processes –
more uncertainty?
Challenges for Decadal Prediction:
Initialisation and Evaluation
Decadal predictions of global annual mean
surface temperature
Observations
Forecast/hindcast
Forecast from 2008
Forecast from 2009
Smith et al., 2007
Impact of initialisation on hindcast skill
5 year mean (JJASON) surface temp
15x15 degrees
DePreSys anomaly correlation
DePreSys-NoAssim correlation
• HadCM3
• 9 member perturbed physics ensemble
• Starting every Nov from 1960 to 2005
Improved predictions of multi-year
Atlantic hurricane frequencies
5-year mean JJASON number of model storms
(coloured) and observed hurricanes (black)
NoAssim
Normalised anomaly
DePreSys
Skill comes from SSTs in tropical Pacific and N. Atlantic subpolar gyres, and from wind shear in hurricane development
regions
Sub-surface ocean observations: A limiting
factor in estimating skill and predictability
1960
1980
2007
• Need historical tests to assess likely skill of
forecasts
• Far fewer sub-surface ocean observations in
the past
Doug Smith, Met Office Hadley Centre
Temperature at 300m :
June 2007 from 1960 observational base
June 2007 obs
Analysis using all obs
June 1960 obs
Analysis using sub-sampled (1960) obs
Variability versus
Anthropogenic Forcing of
the
Physical Climate System
20 centuries of NINO3 SSTs
annual means & 20yr low-pass
Major uncertainty in
Chemistry-Climate
Interactions
Coupled Chemistry-Aerosol-Climate model
Clear Sky
Cloudy Sky
SW Radiation
Activation
Droplets
Aerosols
Atmosphere
LW Radiation
Sea Ice
Evaporation
Surface
Flux
Ocean
SST
Mixed-Layer
Deep Ocean
Global Air Quality and Climate
Precipitation
Land
Aerosols and Climate
Aerosol-Cloud Interactions in GFDL’s Newest Physical
Climate Model (CM3)
Comparison of Simulated Aerosol Properties with Observations
Radiative Flux Perturbation
w/m2
M
O
D
E
L
Direct effects –
Sulfate and
organic carbon
Observations (AERONET)
Direct effects Black carbon
CM3
CM2.1
~0
-1.3
(assuming
internal
mixing of
sulfate and
black carbon)
(external mixing)
0.5
(external mixing)
M
O
D
E
L
Indirect effects
-1.3
Not included
Observations (AERONET)
20
Capturing High-Resolution
Phenomena
Atlantic Hurricanes in a
Warming World
Most recent GFDL downscaling study (Bender et al, Science, 2010)
see https://www.gfdl.noaa.gov/21st-century-projections-of-intense-hurricanes
Uses two downscaling steps:
Global CMIP3 models => regional model of Atlantic hurricane season
regional model => operational GFDL hurricane prediction system
Conclusion: Best estimate is for
doubling of cat 4-5 storms in Atlantic by end of century,
despite decrease in total number of tropical cyclones
Much of the uncertainty arises from global model input
Conclusions I
• Emerging need for centennial and decadal
projections. They pose similar and differing
challenges.
• Earth system processes potentially
increase uncertainty in centennial
projections, especially in the upper range
of warming.
• Initialising decadal projections can
reduce uncertainty at least for a few
years ahead.
Conclusions II
• Observations of the sub-surface ocean
and the full earth system may limit our
ability to provide more confident
projections.
• Natural variability in the context of
forced change is challenging.
• High resolution modelling is opening up
new avenues for more detailed projections
of regional climate change and high
impact phenomena.