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© Crown copyright Met Office
Decadal Climate PredictionDoug 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
“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
UK 9-year mean temperature
© Crown copyright Met Office
El Niño Southern Oscillation (ENSO)
Smith et al, 2011
© Crown copyright Met Office
Atlantic multi-decadal variability (AMV)
Smith et al, 2011
© Crown copyright Met Office
Impact of Atlantic on Europe?
(Sutton and Dong 2012)
© Crown copyright Met Office
Impact of Atlantic on Europe?
(Sutton and Dong 2012)
© Crown copyright Met Office
Potential climate impacts of North Atlantic sea surface temperatures
North Atlantic SST
Sahel rainfall
India rainfall
Hurricanes
(Zhang and Delworth, 2006)
© Crown copyright Met Office
Atlantic ocean circulation
(Dunstone and Smith 2010)
• Idealised experiments suggest that North Atlantic ocean currents are potentially predictable on decadal timescales
Full depth observations Observations in upper 2000m
10 20 30 40 50
Year
10 20 30 40 50
© Crown copyright Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Sub-surface ocean observations
19801960 2007
• Need historical tests to assess likely skill of forecasts
• Far fewer sub-surface ocean observations in the past
© Crown copyright Met Office(Hawkins and Sutton, 2011)
Uncertainties
• Large uncertainties in model response to external forcing• Need multi-model ensembles• and to understand physical mechanisms
Projections of Dec-Feb decadal rainfall
© Crown copyright Met Office
Time
Tem
peratu
re
Ensembles of forecasts:• Uncertainties in the initial conditions• Model errors
Forecasts
Actual
An optimistic view:
Uncertainties
Not accounted for:• Uncertainties in greenhouse gas and aerosol emissions• Volcanoes, changes in solar output
© Crown copyright Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office(Smith et al. 2010)
Surface temperature predictions(five year means)
Initialised - UninitialisedSkill of initialised predictions
• Skilful almost everywhere (positive correlations)
• Mostly due to external forcing
• Initialisation gives improved skill mainly in North Atlantic and tropical Pacific
© Crown copyright Met Office (Pohlmann et al. 2011, in revision)
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
© Crown copyright Met Office(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
© Crown copyright Met Office
North Atlantic sub-polar gyre (SPG)
(Robson et al. 2012, also Yeager et al. 2012)
SPG 500m temp
Meridional heat transport
Overturning circulation
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 Met Office
Impacts of 1995 SPG warming
(Robson et al. 2012)
Tem
pera
ture
Pre
cipi
tatio
n
• Initialisation impacts temperature and precipitation following the 1995 SPG warming
© Crown copyright Met Office
Tropical storm predictions beyond the seasonal range
(Smith et al. 2010)
Skill from external forcing and initialisation
5 year means
Initialised
Uninitialised
Observations
Initialised
Uninitialised
Persistence
© Crown copyright Met Office
Remote influences on Atlantic hurricanes
(Smith et al. 2010)
© Crown copyright Met Office(Eade et al. in press)
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 Met Office(Eade et al. in press)
Skill of wet extremes
• Assessed from daily data
• Wet: precipitation rate greater than 90th percentile (of rainy days)
© Crown copyright Met Office
Contents
• Motivation for decadal predictions
• Practical issues
• Initial results
• Future priorities
© Crown copyright Met Office
Multi-model forecasts of 2011
(Smith et al. submitted)
© Crown copyright Met Office
Impact of initialisation 2012-16
Initialised – uninitialised, stippled where not significant
(Smith et al. submitted)
© Crown copyright Met Office
Solar variability : winter(solar min – solar max)
Model Observations
Ineson et al., 2011, NGEO
Winter sea level pressure, solar min minus solar max
© Crown copyright Met Office
Arctic Sea Ice
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
Recent Winter Pressure
Reproduced by Climate Model
© Crown copyright Met Office
Better models:skill for temperature years 2-5
Old modelNew model Difference
© Crown copyright Met Office
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
© Crown copyright Met Office
Thank youAny questions?