1. Hadley Centre © Crown copyright 2004 The CLIVAR International Climate of the Twentieth Century (C20C) Project 1. History and aims 2. Methodology and approach 3. Forcing data sets 4. Some achievements 5. Future development of C20C and issues Chris Folland, Hadley Centre, Met Office & Jim Kinter, COLA 4 th Climate of the Twentieth Century Workshop, Exeter 13- 15 March, 2007

2. Hadley Centre © Crown copyright 2004 Purpose and basic methodology  Initially focused on AGCMs all forced with same HadISST sea surface temperature and sea ice analysis  Characterize variability, trends and predictability of climatic conditions and events of the past ~130 years associated with various slowly varying forcing functions including SST  Differs from AMIP in NOT being primarily focused on model validation and with strong multi-annual to multi- decadal variability (predictability and understanding aspects) focus. AMIP only c. 20 years, C20C 130 years.

3. Hadley Centre © Crown copyright 2004 Approach  Period of interest: 1871-current  Organization:  Jointly organized by Hadley Centre, UK & Center for Ocean-Land- Atmosphere Studies (COLA), USA  24 different modeling groups participating internationally  CLIVAR project & reporting to WMO/CAS/WGNE  Now includes many other forcing data sets, including greenhouse gases, ozone, volcanic aerosols and solar variability, but not uniformly across groups yet.  Now expanded to include use of “Pacemaker experiments” and coupled models in order to more accurately simulate modes of variability that are inherently coupled and to understand mechanisms.

4. Hadley Centre © Crown copyright 2004 Contributions of C20C C20C contributes to:  Seasonal to interannual predictability  Decadal to interdecadal variability & predictability  Understanding climate trends  Model evaluation

5. Hadley Centre © Crown copyright 2004 Chronology  Project initiated by Hadley Centre  several informal bilateral collaborations established  1 st workshop held at Hadley Centre in Nov 1994  Input to 1995 IPCC assessment and special session at 1 st international AMIP conference in 1995  Revitalized by Hadley Centre with strong COLA infrastructure support.  1998 invitation to several modeling groups  infrastructure provided by COLA (www.iges.org/c20c; GDS)  2 nd workshop held at COLA in Jan 2002 (reported in CLIVAR Exchanges, Jun 2002)  Agreed set of runs with updated forcing data sets, diagnostics and special projects  C20C established as official CLIVAR project in January 2003  Third Workshop - 19-23 Apr 2004, ICTP, Italy  Special Meeting July 2005, Prague, Czech Republic

6. Hadley Centre © Crown copyright 2004 Phases of C20C activity since 1999 Phase 1 (prior to 2003): SST and sea ice changes  Hadley Centre provides HadISST1.1 SST and sea ice data set as lower boundary conditions  Integrate over 1871-2002 (at least 1949-2002)  Ensembles of at least 4 members Phase 2 (2003 - ): include atmospheric composition changes  Greenhouse gases – CO 2, O 3, etc.  Aerosols (volcanic)  Solar variability  Hadley Centre can provide a full set of forcings Phase 3 ( 2007 - 2011): “Pacemaker” experiments, much more emphasis on land surface /diurnal variation of SST/ better SST and sea ice  Land surface forcing (version already in Hadley Centre model) and special experiments  Explore influence of diurnal variation of SST in HadiSST1  More highly resolved HadISST2 from 2009.

7. Hadley Centre © Crown copyright 2004 Special Topics  Predictability and understanding of seasonal to multi-decadal phenomena  1930s drought in USA (“Dust Bowl”)  1962-63 European winter (links to NAO time series work)  Autumn 2000 western European floods  2003 European heat wave  Interdecadal variations of summer climate over Europe and North Atlantic.  Decadal modulation of responses to ENSO  Time series – variations, trends and their causes  SOI, NAO, PNA, Asian monsoon rainfall, Sahel rainfall, Nordeste of Brazil rainfall, MJO trends  Global and regional land surface air temperature trends  Others, e.g., river runoff trends  Use of new diagnostic methods in climate variability studies

8. Hadley Centre © Crown copyright 2004 Key Validating Data Sets  NCEP/NCAR Reanalysis (1948-now)  ERA40 Reanalysis (1958-2002)  HadSLP global monthly sea level pressure analysis updated with modified NCEP (1871-2007)  New EMSLP daily sea level pressure data set over extratropical N Atlantic and Europe 1871-2003  Brohan et al land surface air temperature data (1850- now) and Hulme land surface rainfall analyses (1871-now)  Xie-Arkin global precipitation analysis (1979-now)

9. Hadley Centre © Crown copyright 2004 Report of the C20C Prague Special Meeting, 2005

10. Hadley Centre © Crown copyright 2004 Key Proposals of the 2005 Prague Special Meeting for future coordinated C20C experiments

11. Hadley Centre © Crown copyright 2004 Links to WCRP  C20C became a CLIVAR activity in Jan 2003  Also reports to Working Group on Numerical Experimentation (WCRP/CAS/WGNE)  Need to strengthen our links to the Working Group on Seasonal to Interannual Prediction. How should we do this? Exploratory meeting involving CKF in autumn 2004.

12. Hadley Centre © Crown copyright 2004 Three contrasting examples of recent C20C published papers

13. Hadley Centre © Crown copyright 2004 from Schubert et al. 2004 (Science, 19 Mar2004) Simulating Dust Bowl era drought

14. Hadley Centre © Crown copyright 2004 Effect on the winter NAO of imposing observed stratospheric winds at 50hPa on HadAM3 Change in NAO index Change in surface pressure Model also forced with HadISST and all known major forcings in C20C mode. Full NAO and surface climate change 1965-95 reproduced From Scaife et al, 2005, GRL

15. Hadley Centre © Crown copyright 2004 Secular increase in predictability of boreal winter mean temperature over land, 1897- 1998, using two models mainly caused by decadal changes in ENSO variability Kang et al, 2006, GRL, highlighted