Sea level projections with semiempirical and earth system models

Transcription

1 Sea level projections with semiempirical and earth system models John C. Moore College of Global Change and Earth System Science, Beijing Normal University, Beijing, China and Arctic Centre, University of Lapland, Finland with contributions from Svetlana Jevrejeva, Bill Lipscomb and Aslak Grinsted

2 Global sea level rise 21 st century Global sea level rise will affect hundreds of millions of people on our planet. World Bank, million people for 1 m rise (USGS) It is critical to get projections right for the planning of infrastructure: Flooding in Myanmar caused by Tropical cyclone Nargis 30 cm of sea level rise can mean that extreme events you thought would happen once in 1000 years will instead happen once in 10 years! Images: NASA/MODIS Rapid Response Team

3 Greenland Mass Loss Khan et al. Geophys Res Lett, 2010

4 IPCC AR4 (2007): cm of sea-level rise by 2100 (excluding ice-sheet dynamic effects) Rahmstorf 2007: cm (semi-empirical model) Sea-level predictions to date Jevrejeva et al. 2010: cm (semi-empirical statistical model) Pfeffer et al. 2008: cm (kinematic constraints for ice sheets) AR4 The IPCC AR4 projections are almost certainly too low. The most credible current predictions are based on semi-empirical relationships between global mean surface temperature or radiative forcing and sea-level rise. These simple relationships may not hold in the future as new physical processes come into play (e.g., ice-sheet dynamic feedbacks). Realistic physical models are needed to better bound the range of uncertainty.

5 Sea-level prediction with Earth-system models Most ESMs already have some of the components needed for physically based sea-level predictions: e.g., a fully coupled atmosphere-ocean GCM that can provide ocean thermal expansion and dynamic SLR. What s missing? Dynamic ice-sheet models Higher-order or full-stokes dynamics for fast flow in ice streams and outlet glaciers Realistic treatment of physical processes (e.g., subglacial water transport, basal sliding, iceberg calving) Fine grid resolution (~1 km) Coupling of ice-sheet models to other climate components Ice-atmosphere coupling (for surface mass balance) Ice-ocean coupling (for retreat of marine-based ice) Improved models of glaciers and ice caps (using scaling relationships) Regional sea-level variations from self gravitation, elastic rebound, etc. Greenland melt versus West Antarctica melt for Europe

6 Coupled modeling efforts Ice2sea: Large European project aiming to predict land-ice contributions to sea level over the next 200 years Global climate models regional atm/ocean models ice-sheet models (no two-way coupling) JPL: Will couple ISSM dynamically to the MITgcm (used for ECCO ocean data assimilation project) NASA Goddard: Will couple Glimmer-CISM to two NASA climate models (ModelE and GEOS-5) GFDL: Has coupled the GOLD ocean model to an ice-sheet/ice-shelf model for idealized experiments. ISICLES: (Ice Sheet Initiative for Climate ExtremeS) is a 3-year ( ) initiative of the DOE Office of Advanced Scientific Computing Research

7 ISICLES The goal of ISICLES is to use advanced numerical and computational methods (e.g., the Trilinos, PETSc, and Chombo software packages) to develop accurate, efficient, scalable ice sheet and characterize their uncertainties. Greenland surface ice velocity (log 10 scale), 2-km grid, higher-order flow model (courtesy of S. Price) Antarctic surface ice velocity on adaptive mesh (courtesy of D. Martin)

8 Ice-ocean coupling Recent Antarctic mass loss has been driven by intrusions of warm Circumpolar Deep Water beneath marine ice sheets Modest changes in wind forcing could drive large changes in delivery of warm CDW to the base of ice shelves. Models suggest that marine ice sheets on reverse-sloping beds (e.g., West Antarctica) could retreat unstably. Schematic of warm CDW reaching the grounding line (courtesy of A. Jenkins) Topography of Pine Island Glacier (courtesy of A. Jenkins)

9 Semi-empircal models Rahmstorf, S A semi-empirical approach to projecting future sea-level rise, Science, 315, Horton et al, Sea level rise projections for current generation CGCMs based on the semi empirical method, Geophys. Res. Lett., 35, L02715, doi: /2007gl Vermeer, M. and S. Rahmstorf Global sea level linked to global temperature, Proceedings of the National Academy of Science of the USA, /pnas Grinsted, A., J. C. Moore and S. Jevrejeva Reconstructing sea level from paleo and projected temperatures 200 to 2100AD, Clim. Dyn., doi: /s Jevrejeva, S, J.C. Moore and A. Grinsted How will sea level respond to changes in natural and anthropogenic forcings by 2100?, Geophys. Res. Lett., 37, L07703, doi: /2010gl042947

10 Model including a response time (Grinsted et al, 2009) S = at + b eq (eq. 1) S=f(T) Parameters: (, a, b, S 0 ) Grinsted et al Reconstructing sea level from paleo and projected temperatures 200 to 2100AD, Clim. Dyn., doi: /s

11 Inverse problem We know T (Temperature, or radiative forcing 2000 yrs) We know S (Tide gauges, 300 yrs) a, b,, S 0 Grinsted et al Reconstructing sea level from paleo and projected temperatures 200 to 2100AD, Clim. Dyn., doi: /s

12 Forcing (W/m2) model: S=f(T)

13 Anthropogenic and natural forcing of sea level IPCC AR4 WG1

14 Anthropogenic and natural forcing of sea level 4 forcings Tide gauges No volcanoes GHG caused No GHG Jevrejeva, S., et al (2009) Anthropogenic forcing dominates sea level rise since 1850, Geophysical Research Letters

15 Jevrejeva et al., submitted Grinsted et al., 2009

16 Validation: post 1990 response Grinsted et al Reconstructing sea level from paleo and projected temperatures 200 to 2100AD, Clim. Dyn., doi: /s

17 Validation: Volcanic signature Pinatubo 1991 Tambora 1815 S-E ESM ESM S-E Moore et al, PNAS, 2010

18 Plan B

19 Keith, David, 2001: Geoengineering, Nature, 409, 420.

20 Geoengineering is continuous and has no damage costs Goes et al., Climatic Change in press

21 Short summary No high SRES Sea level by 2100 Uncertainty of rise in cm is equivalent to uncertainty in date