Why are we here?

Key Impacts of climate change in the coastal zone Sea-level rise –inundation –storm surges, waves –coastal erosion –Impacts on emergency and escape routes –Break down in law and order –Environmental refugees – a here and now issue not “if” but “when and where and how will we respond?”

People to respond -Tens of millions (far fewer with optimum protection) Can measure sea- level rise in other units! Wide range of projections Church et al., 2001

Despite all of the uncertainties we do know quite a lot.

Reconstructed sea level for 1870 to 2000 indicates an acceleration of the rate of sea-level rise Church and White, 2006

Estimates of thermosteric sea level rise from 1993 – 2003 using a variety of analysis techniques (Willis et al., 2004, Lombard et al., 2005, Domingues et al., 2006) are similar, about 1.6 mm/yr (about 1.3 mm/yr for OI estimates), but with interannual differences. All of these are strongly dependent on XBT data. Does the 1998 ENSO signal seen in sea level have a thermosteric component? Domingues et al., 2006 Willis et al., 2004, Lyman et al Lombard et al., estimates of upper ocean thermosteric sea level rise, Calculations with a common dataset are needed to reconcile these differences.

Glaciers contribution to sea level From Position Paper ‘Cryospheric Contributions’ 0.8 +/- 0.4 mm/yr

Contribution of Ice sheets to Sea Level From Position Paper ‘Cryospheric Contributions’ Zwally et al. (2005) Krabill et al. (2004) Thomas et al. (2006) Vellicogna and Wahr (2005) Ramillien et al. (2006) Rignot & Kanagaratnam (2006) 1. Greenland 2. Antarctica : « probable net loss but close to balance » 0.3 +/ mm/yr A major improvement – decreased uncertainty by a factor of 3+!

Antarctic current ice evolution from glaciological modeling -> Antarctic ice sheet at the tail end of the last glacial-interglacial transition: still responding to WAIS grounding line retreat since LGM, but close to minimum with only small remaining trend Huybrechts, QSR, 2002

Sea level (m) before present Coral data Serpulid data Archaeological Tide gauge Paleo data opportunities Extending historical data over centuries to millenia Constraining Ice Sheet contributions

Increasing concern about ice-sheet stability and a substantially larger rise in sea level Surface melting Dynamic instability

Effect of global land water storage on global mean sea level agreement between ORCHIDEE and LaD. (Land Dynamics LSM of GFDL) greatest variation is associated with ground water, followed by soil moisture no significant trend was detected strong decadal variability driven by precipitation, strong decrease in the beginning of 1970s Milly, P. C., D., A. Cazenave, and M. C. Gennero (Proc. Natl Acad. Sci, 2003) Ngo-duc T., K. Laval, J. Polcher, A. Lombard and A. Cazenave (GRL, 2005)

Threats: ITRF on “shaky ground”: current collocations –Links between SLR-VLBI-GNSS are weakening in time –Uneven station distribution leads to biases –No long-term systematic commitment to support ITRF (2)(16)(59)(8) We now have an ITRF – need to support it through GGOS and GEOSS

Viscous “Memory” of Solid Earth to Past Ice-Ocean Mass Flux

Emanuel’s Multi-basin Tropical Cyclone Power Dissipation Index (PDI) has increased substantially over past 50 years, along with tropical SSTs Source: Kerry Emanuel, MIT, SST anomaly (deg C) with arbitrary vertical offset. PDI scaled by constant.

Webster et al.: The percentage of hurricanes which reach Category 4-5 has increased in all basins, comparing two recent 15-year periods… Question: Are the historical data adequate for this conclusion? Source: Adapted from Webster et al., Science, Sept

Integration

First Example: Small Number of Tide Gauges Mitrovica et al., 2001 Tamisiea et al., 2001

We can make progress in closing the budget!

Integration – Next steps?

Need to present probabilities – risk based framework

20C AOGCM simulated global mean sea level Volcanoes (Krakatoa 1883; Agung 1963; El Chichon 1982) explain part of the spread over 140 simulation years PCMDI, modelling groups, J. Gregory

Simulated vs. observed thermosteric sea level rise J. Church (pers. comm. 2006)