Colorado Center for Astrodynamics Research University of Colorado at Boulder

1. An assessment of IPCC 20th century climate simulations using the 15-year sea level record from altimetry Eric Leuliette, Steve Nerem, and Thomas Jakub University of Colorado, USA Colorado Center for Astrodynamics Research University of Colorado at Boulder

2. Outline • IPCC coupled climate models • 20th century climate experiment output compared to • sea level reconstructions • observed thermosteric sea level change • TOPEX/POSEIDON observations • Global mean sea level • Regional variations

3. IPCC/CMIP • The Intergovernmental Panel on Climate Change Fourth Assessment Report (FAR) will be issued in 2007 • Coupled Model Intercomparison Project • 23 climate models from 16 institutions • Output variables include • Total sea level change • Steric sea level change

4. 3rd Assessment Report 2001: 21st century predictions have little agreement

5. Experiment Name Period Initial condition IPCC scenarios pre-industrial control > 100 years No anthropogenic or natural forcing present-day control > 100 years No natural forcing and anthropogenic influences will be set at present-day level. climate of the 20th century (20C3M) ~1850 - present pre-industrial control committed climate change present - 2100 end of the 20C3M run SRES A2 present - 2100 end of the 20C3M run 720 ppm stabilization (SRES A1B) present - 2300 end of the 20C3M run 550 ppm stabilization (SRES B1) present - 2300 end of the 20C3M run +1%/year CO2 (to doubling) ~70 yrs to 2x +150 present-day control or a pre-industrial control +1%/year CO2 (to quadrupling) ~140 yrs to 4x +150 pre-industrial control or a present-day control

6. IPCC models reporting sea level time series IPCC models CGCM3.1 T47 Canadian Center for Climate Modelling and Analysis GISS AOM NASA/Goddard Institute GISS E20/Russell NASA/Goddard Institute INMCM 3.0 Institute for Numerical Mathematics, Russia MIROC 3.2 hires CCSR/NIES/FRCGC, Japan MRI CGCM2 3.2 Meteorological Research Institute, Japan

7. Climate models • Climate models are designed to simulate long-term variability. • Coupled climate models are forced with natural and anthropogenic atmospheric conditions. • We should not expect the models to reproduce some observed interannual variability (i.e. ENSO).

8. Reconstruction • Sea level Reconstruction • Method similar to Chambers et al. [2002] and Church et al. [2004] • Uses altimetry data decomposed into a number of empirical orthogonal functions (EOFs). • Employs a fit of spare tide gauge data to EOF spatial maps to reconstruct global variability. • Assumes that ~13 years of altimetry spans significant multi-decadal variability.

9. Reconstruction (2) • Reconstructions two different methods • 1) EOFs produced directly from T/P and Jason altimetry (with seasonal signal removed) • 2) Detrended data + eustatic “EOF0” • Tide gauges selection criteria: Chambers et al. [2002] • Error analysis uses model output to estimate the impact of multi-decadal variability not spanned by the EOFs.

10. Global mean sea level • GMSL 1930-2000

11. GMSL TP-era • GMSL 1992-2004

12. Reference Thermosteric sea level change(mm/year) Period Depth range (meters) Data Steric sea level Antonov et al. (2005) 0.40 ± 0.05 1955-1998 0-3000 Levitus et al. (2005b) Antonov et al. (2005) 0.34 ± 0.04 1955-2003 0-700 Levitus et al. (2005b) Ishii et al. (2005) 0.38 ± 0.04 1955-2003 0-700 Ishii et al. (2005) Antonov et al. (2005) 1.23 ± 0.2 1993-2003 0-700 Levitus et al. (2005b) Ishii et al. (2005) 1.8 ± 0.2 1993-2003 0-700 Ishii et al. (2005) Willis et al. (2005) 1.6 ± 0.3 1993-2003 0-750 Willis et al. (2005)

13. Model GMSL (mm/yr) Thermosteric (mm/yr) ratio GMSL vs TSL CGCM3.1 –0.03 –0.09 3.00 GISS AOM 1.74 1.15 0.66 GISS E20/Russell 0.87 0.72 0.83 INMCM 3.0 1.28 1.25 0.98 MIROC 3.2 hires 1.04 0.98 0.94 MRI CGCM2 3.2 1.58 1.85 0.85 Observations 1.8 ± 0.3 20th century average trends (1900-2000)

14. Thermosteric (1955-2000)

15. Model GMSL (mm/yr) Thermosteric (mm/yr) ratio GMSL vs TSL CGCM3.1 0.74 0.56 0.76 GISS AOM 3.42 2.04 0.60 GISS E20/Russell 1.12 0.88 0.79 INMCM 3.0 1.25 1.33 1.06 MIROC 3.2 hires 1.16 1.19 1.03 MRI CGCM2 3.2 2.56 3.19 1.25 Observations 1.8 ± 0.3 0.40 ± 0.05 0.22 ± 0.05 late 20th century trends (1955-2000)

16. Model GMSL (mm/yr) Thermosteric (mm/yr) ratio GMSL vs TSL CGCM3.1 0.32 0.79 0.40 GISS AOM 6.11 3.51 0.57 GISS E20/Russell 1.99 0.72 0.36 INMCM 3.0 1.34 1.38 1.03 MIROC 3.2 hires 2.71 2.32 0.85 MRI CGCM2 3.2 3.98 5.69 0.70 Observations 3.1 ± 0.5 1.5± 0.4 0.48±0.05 T/P-era average trends (1992-2000)

17. Regional trends • TOPEX/Poseidon and Jason altimetry

18. Regional trends • GISS AOM (1990-2000)

19. Regional trends • NCAR CCSM 3.0 (1990-2000)

20. Regional trends • UKMO HADCM3 (1990-2000)

21. Regional trends • MIROC 3.2 (1990-2000)

22. Regional trends • TOPEX/Poseidon and Jason altimetry

23. Summary • IPCC FAR models generally underestimate the observed sea level change during the 20th century. T/P-era rates vary from 0.3-6.1 mm/yr. • The magnitude of steric sea level change and its contribution to total sea level change is overestimated over the 20th century. • Some high-resolution models appear to reproduce the magnitude and some of the geographical distribution of sea level change during the TOPEX/Poseidon-era.