Cross-Cutting Topic DECADAL PREDICTION

Examples of Decadal Climate Anomalies Which Have Gone Down in Folkore Southern US Dustbowl (Grapes of Wrath) Sahel Drought (Band Aid)

CLIVAR Panels Contributing to Input to Decadal Paper VACS WGSIP US CLIVAR WG on multi-year drought Atlantic Panel Pacific Panel SPARC Dynamical impacts Chemical impacts

Why Now? Global Ocean-Atmosphere re-analyses are being produced over the last 50 years Coupled models are starting to be run on decadal timescales from these analyses

Atlantic Meridional Transport at 26N Upper 1200m (Balmaseda et al, 2007) Bryden Trend=-0.159 +/- 0.162 Sv/y -8.7% per decade Assimilation Trend= -0.074 +/- 0.020 Sv/y. -4.% per decade Surface fluxes only Trend= -0.029 +/- 0.013 Sv/y. -2% per decade Climatology Trend= -0.009 +/- 0.006 Sv/y -0.6% per decade

Volume transport upper 2000m (x20Sv) Heat Transport (x1 PW)

Decadal Climate Predictions at the Hadley Centre Doug Smith, James Murphy, Stephen Cusack A decadal prediction system (DePreSys) has been built Based on ensemble runs of HadCM3 started from analysed fields of observed anomalies of ocean T and S, and atmosphere wind, temperature, surface pressure Forecasts include GHG, aerosol forcing (SRES B2) Forecasts repeat previous 11 year solar cycle, and decay volcanic aerosol from initial conditions (i.e. assume no prior knowledge of future eruptions) Do we achieve additional skill by starting the model from observed initial conditions ? Test by running a set of DePreSys ensemble hindcasts, started from 1st March, June, September and December in each year from 1982 to 2001 (20 years x 4 seasons = 80 start dates) Compare against a parallel set of runs (NoAssim), which include the same external forcings as DePreSys but omit the assimilation of observed initial conditions (No Assim runs are started from initial states taken from HadCM3 “all forcings” simulations of historical climate change.) © Crown copyright 2004

Skill for SAT (years 5-10) Keenlyside et al. 2007

Coordinated Decadal Predictions are beginning within EU ENSEMBLES project

Proposal for Coordinated WCRP coupled model experimentation A:1965 initial conditions, observed GHGs and aerosols from 1965 B:1994 initial conditions, observed GHGs and aerosols from 1994 C:1965 initial conditions, observed GHGs and aerosols from 1994 D:1994 initial conditions, observed GHGs and aerosols from 1965 Hence (A-B)  overall level of predictability (A-D) & (B-C)  impact of initial conditions (A-C) & (B-D)  impact of GHG forcing

Relevance to WCRP: i Science From a scientific point of view the time is ripe for WCRP to start organising coordinated experimentation to assess decadal prediction skill from analysed initial conditions Decadal prediction will be a natural “meeting ground” for the weather and climate modelling communities and hence implementation of seamless strategy. Proposal links in with other projects eg EU ENSEMBLES

i Science (continued) The overarching objectives of WCRP are: To determine the effect of human activities on climate To determine the predictability of climate The proposed coordinated study addresses both of these objectives – the intrinsic predictability of climate, ie the role of initial conditions, and the anthropogenic forcing of climate.

ii Policy Relevance Many applications in health, agriculture, water management, tourism, forestry, fisheries, hurricane prediction, shipping and offshore construction, power generation… Key WCRP contribution to the problem of climate adaptation. It is possible that AR5 will include a chapter on hi-res decadal timescale predictions (eg to 2030). It is important for WCRP to play a leading role in this area.

iii Organisation and Governance Proposal draws on expertise of scientists across whole range of WCRP. Scoping of proposed activity should be carried out by short-period pan-WCRP Task Force lead by CLIVAR and involving experts from CliC, GEWEX and SPARC, reporting on progress to WMP and WOAP, aiming for the development of a more comprehensive plan for the initial experiment for JSC XXIX.

iv Visibility and communication by WCRP Great opportunities for the visibility of WCRP, emphasising the need for “short-term” climate predictions for climate adaptation purposes.

v Interaction with other bodies IGBP CLIPS IPCC

vi Capacity building in/by WCRP Decadal prediction will provide a focus for development of capacity in terms of seamless prediction and linkage between weather and climate prediction institutes. Potential for a wide range of prediction services, building capacity for planning across the developed and developing world.

Update June 2007 Proposal endorsed by JSC Now ready to start discussion with the community Please send comments and your interest in participating in WCRP cross-cutting decadal prediction activity to me (tim.palmer@ecmwf.int) A more definitive (eg DEMETER-like) multi-model study will be proposed after this first proof-of-concept phase has been assessed.