Decadal Climate Prediction
Doug Smith, Nick Dunstone, Rosie Eade, Leon Hermanson, Adam
Scaife
© Crown copyright Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Decadal prediction
UK 9-year mean temperature
“Global warming” trend
Natural internal variability, or errors in
simulation of external forcing
• Need to take into account all sources of predictability
• External forcing: greenhouse gases, aerosols, volcanoes, solar
• Natural internal variability – need to start predictions from the
current state of the climate system
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El Niño Southern Oscillation (ENSO)
© Crown
copyright
Smith
et al,
2011Met Office
Atlantic multi-decadal variability (AMV)
© Crown
copyright
Smith
et al,
2011Met Office
Impact of Atlantic on Europe?
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(Sutton and Dong 2012)
Impact of Atlantic on Europe?
© Crown copyright Met Office
(Sutton and Dong 2012)
Potential climate impacts of North
Atlantic sea surface temperatures
North Atlantic SST
Sahel rainfall
India rainfall
Hurricanes
© Crown copyright
Met Office 2006)
(Zhang
and Delworth,
Atlantic ocean circulation
• Idealised experiments
suggest that North Atlantic
ocean currents are
potentially predictable on
decadal timescales
Full depth observations
10
20
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30
Year
40
Observations in upper 2000m
50
10
20
30
40
50
(Dunstone and Smith 2010)
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Sub-surface ocean observations
1960
1980
2007
• Need historical tests to assess likely skill of
forecasts
• Far fewer sub-surface ocean observations in
the past
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Uncertainties
Projections of Dec-Feb decadal rainfall
• Large uncertainties in model response to external forcing
• Need multi-model ensembles
• and to understand physical mechanisms
© Crown copyright
Office 2011)
(Hawkins
and Met
Sutton,
Uncertainties
Ensembles of forecasts:
• Uncertainties in the initial conditions
• Model errors
An optimistic view:
Forecasts
Temperature
Actual
Time
Not accounted for:
• Uncertainties in greenhouse gas and aerosol emissions
• Volcanoes,
changes in solar output
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copyright Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Surface temperature predictions
(five year means)
Skill of initialised predictions
Initialised - Uninitialised
• Skilful almost everywhere (positive correlations)
• Mostly due to external forcing
• Initialisation gives improved skill mainly in North Atlantic
and tropical Pacific
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Office
(Smith
et al.Met
2010)
AMOC at 45oN in assimilation
experiments
• No historical observations – must rely
on models
• Consistent signal: increase from 1960
to 1995, decrease thereafter
• Agrees with related observations
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(Pohlmann et al. 2011, in revision)
AMOC at 45oN in hindcast
experiments
Initialised hindcasts
Externally-forced hindcasts
• Some skill in initialised predictions, but not in uninitialised predictions
(Pohlmann
et al. 2011, in revision)
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North Atlantic sub-polar gyre
Meridional heat
Overturning
(SPG)
transport
circulation
SPG 500m temp
Observations
Initialised (DePreSys)
Uninitialised
(NoAssim)
• Improved skill for 1995 rapid warming results from initialisation of increased Atlantic
overturning circulation and meridional heat transport
© Crown
copyright
(Robson
et al.
2012, Met
alsoOffice
Yeager et al. 2012)
Precipitation
Temperature
Impacts of 1995 SPG warming
• Initialisation impacts temperature and precipitation following the 1995 SPG warming
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(Robson et al. 2012)
Tropical storm predictions
beyond the seasonal range
Initialised
Uninitialised
Persistence
Skill from external forcing
and initialisation
5 year means
(Smith et al. 2010)
Initialised
Uninitialised
Observations
© Crown copyright Met Office
Remote influences on Atlantic
hurricanes
(Smith
et al. 2010)
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Skill of temperature extremes
• Hindcasts start Nov 1st each year 1960 to 2005, with 9 ensemble members
• Assess extremes using daily data
• Moderate extremes (10th percentile)
• 4 definitions (e.g. cold days, cold nights, warm days, warm nights)
© Crown
copyright
(Eade
et al. in
press)Met Office
Skill of wet extremes
• Assessed from daily data
• Wet: precipitation rate greater than 90th percentile (of rainy days)
© Crown
copyright
(Eade
et al. in
press)Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Multi-model forecasts of 2011
© Crown
Met Office
(Smith
et al.copyright
submitted)
Impact of initialisation 2012-16
Initialised – uninitialised, stippled where not significant
© Crown
Met Office
(Smith
et al.copyright
submitted)
Solar variability : winter
(solar min – solar max)
Model
Observations
Winter sea level pressure, solar min minus solar max
© Crown
copyright
Office
Ineson
et al.,
2011,MetNGEO
Arctic Sea Ice
Recent Winter Pressure
Arctic Sea Ice is systematically melting
Last few years have seen record melt
Observed climate records and climate
models indicate cold easterly winter
winds in response to ice melt
Reproduced by Climate Model
© Crown copyright Met Office
Better models:
skill for temperature years 2-5
New model
© Crown copyright Met Office
Old model
Difference
Summary
• Already have skill from climate change signal
Skilful predictions of extreme temperatures
• Initialisation improves N. Atlantic and tropical Pacific
Improved predictions of AMOC and SPG
• Skilful predictions of tropical Atlantic storms
• Emerging importance of external factors: aerosols, volcanoes,
solar, greenhouse gases via sea ice?
• Need improved models to predict atmospheric response over
land better
• Need to understand physical mechanisms to gain confidence in
forecasts
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Thank you
Any questions?
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